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<h1>Ctemplate System Reference Guide</h1>
<small>(as of
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<br>


<h2> Overview </h2>

<p>The main class used by the template system is
<code>TemplateDictionary</code>, which is used to expand a template
file.  It is used by the main functions for expanding a template,
found in <code>template.h</code>.</p>

<p><code>TemplateCache</code> is used to hold a collection of
<code>Template</code> objects.  <code>TemplateNamelist</code> provides
various introspection routines on collections of <code>Template</code>
objects.</p>

<p><code>TemplateModifier</code> and <code>PerExpandData</code> are
used to modify the values of a <code>TemplateDictionary</code> at
expand time.  <code>TemplateAnnotator</code> does too, but is intended
for debugging purposes.  <code>TemplateDictionaryPeer</code> is used
for testing template code.</p>

<p><code>ExpandEmitter</code> provides the ability to emit an expanded
template to an arbitrary output store.</p>

<p><code>TemplateString</code> is a string-like class that is built to
be very efficient when used with the template system.  For instance,
tools are available to hash constant <code>TemplateString</code>
objects at compile-time, speeding up their use at run-time.</p>

<p>The rest of this document describes these classes and functions in
more detail, as well as build tools and other mechanisms for handling
templates.</p>

<p>(Note: the code snippets below all assume the default configuration
option is set, which puts template code in namespace
<code>ctemplate</code>.)</p>

<h2> <A NAME="template">Expanding Templates</A> </h2>


<h3> The Template Language </h3>

<p>Templates are strings that contain special formatting code called
<em>template markers</em>.  In the Ctemplate System, template
strings are usually read from a file.</p>

<p>Anything found in a template of the form {{...}} is
interpreted as a template marker.  All other text is considered
formatting text and is output verbatim at template expansion time.
Outside of the template markers, templates may contain any text
whatsoever, including (single) curly braces and NUL characters.</p>

<p>The template language has six types of markers:</p>
<ol>
  <li> <b>Variable</b> markers, which are replaced by text based on
       dictionary values.  Variable markers look like this:
       {{FOO}}</li>

  <li> <b>Start section</b> and <b>end section</b> markers, which
       delimit sections which may appear zero, one, or N times in
       the output.  Section markers look like this:
       <code>{{#FOO}}...{{/FOO}}</code></li>

  <li> <b>Template-include</b> markers, which designate other
       templates to be expanded and inserted at the location where the
       marker appears.  These are treated much like sections -- one
       may think of them as sections whose content is specified in a
       different file instead of inline -- and just like sections, can
       be expanded zero, one or N times in the output, each with a
       different dictionary.  Template-include markers look like this:
       <code>{{&gt;FOO}}</code></li>

  <li> <b>Comment</b> markers, which may annotate the template
       structure but drop completely out of the expanded
       output.  Comment markers look like this:
       <code>{{!&nbsp;comment&nbsp;lives&nbsp;here -- cool, no?}}</code></li>

  <li> <b>Set-delimiter</b> markers, which change the marker
       delimiters from <code>{{</code> and <code>}}</code> to custom
       strings.  (The only requirement is that these strings not
       contain whitespace or the equals sign.)  This is useful for
       languages like TeX, where double-braces may occur in the text
       and are awkward to use for markup.  Set-delimiter markers look
       like this: <code>{{=&lt; &gt;=}} &lt;! Now markers are
       delimited by braces &gt; &lt;=| |=&gt; |! And now markers are
       delimited by bars! | </code></li>

  <li> <b>Pragma</b> markers, which invoke additional built-in template
       features when processing the template. Pragma markers look like
       this: <code>{{%PRAGMA [name="value"...]}}</code>. Currently,
       AUTOESCAPE is the only pragma defined.</li>
</ol>

<p>These marker types each have their own namespace.  For readability,
however, it is best to not overuse a single name.</p>


<h3> Modifiers </h3>

<p>A variable and include-template can have one or more <A
HREF="#template_modifier">modifiers</A> attached to them, like so:</p>
<pre>
   {{MYVAR:mod1:mod2:mod3=value:mod4=value with spaces:mod5}}
</pre>

<p>A modifier is a filter that's
applied at template-expand time, that munges the value of the variable
before it's output.  See the <A
HREF="#template_modifier"><code>TemplateModifier</code></A> class for
more details.</p>

<p>When expanding a variable (or template-include) with a modifier,
the modifiers are applied in order, left to right.  For a
template-include, first the entire sub-template is expanded, as a
single string, and then the modifiers are applied to that string.</p>

<p>In general, using explicit modifiers does not turn off <A
HREF="#auto_escape">auto-escaping</A> on a variable.  The explicit
modifier <code>:none</code> does suppress auto-escaping.</p>


<h3> <A NAME="special_markers">Special Markers</A> </h3>

<p>Some marker names may have a special meaning in the template
system.  Right now, there's one such name.</p>

<h4><A NAME="separator">Separator Sections</A></h4>

<p>If you have a section named FOO, you can define inside
of it a section named FOO_separator, and the template
system will automatically expand that section every time
<code>FOO</code> is expanded, <i>except for the last</i>.  Thus, the
contents of <code>FOO_separator</code> can be used to separate
repeated values of a section.</p>

<p>Here's an example:</p>
<pre>
   Here are the meeting attendees:
   {{#ATTENDEES}}
      {{NAME}}
      {{#ATTENDEES_separator}}, {{/ATTENDEES_separator}}
   {{/ATTENDEES}}
   .
</pre>

<p>Here is a more convoluted example, to show the date:</p>
<pre>
   {{#DATE}}{{DATE_COMPONENT}}{{#DATE_separator}}{{DATE_SEP}}{{/DATE_separator}}{{/DATE}}
</pre>

<p>You'd set up a template dictionary to repeat <code>DATE</code>
three times, with <code>DATE_COMPONENT</code> set to the month, day,
and year (or day, month, and year, depending on your locale...), and
<code>DATE_SEP</code> set to <code>/</code> or <code>-</code> or
whatever date-separator is called for.</p>

<p><code>SEP_separator</code> is always evaluated with the current
dictionary.  Thus, in the date example, if you wanted a different
separator each time, you could do so by setting <code>DATE_SEP</code>
to a different value for each repetition of <code>DATE</code>.</p>

<p>While <code>SEP_separator</code> is automatically expanded by the
template system, it is otherwise a perfectly normal section.  You can
even instantiate it yourself by calling
<code>AddSectionDictionary("SEP_separator")</code>.  In that case, the
section will be expanded both via the automatic expansion as a
separator, and as a normal section via the section dictionary you
added.  This is more confusing than helpful, and you should probably
never do it.</p>

<p>There can be at most one "separator" sub-section per section.  If
there are more, only the last is automatically expanded.</p>


<h3> <A NAME="strip">Specifying a template</A> </h3>

<p>In the template system -- in functions like
<code>ExpandTemplate()</code> -- a template is specified by a pair:
filename + strip-mode.  The filename specifies the name of the
template file on disk (but see below for string templates).  The strip
mode specifies how this file should be parsed as it's read from disk,
in particular, how whitespace should be handled.  It can take the
following values:</p>

<ul>
  <li> <code>ctemplate::DO_NOT_STRIP</code>: do nothing.  This expands
       the template file verbatim.

  <li> <code>ctemplate::STRIP_BLANK_LINES</code>: remove all blank
       lines.  This ignores any blank lines found in the template file
       when parsing it.  When the template is html, this reduces the
       size of the output text without requiring a sacrifice of
       readability for the input file.

  <li> <code>ctemplate::STRIP_WHITESPACE</code>: remove not only blank
       lines when parsing, but also whitespace at the beginning and
       end of each line.  It also removes any linefeed (possibly
       following whitespace) that follows a closing <code>}}</code> of
       any kind of template marker <i>except</i> a template variable.
       (This means a linefeed may be removed anywhere by simply
       placing a comment marker as the last element on the line.)
       When the template is html, this reduces the size of the output
       html without changing the way it renders (except in a few
       special cases.)  When using this flag, the built-in template
       variables <code>BI_NEWLINE</code> and <code>BI_SPACE</code> can
       be useful to force a space or newline in a particular
       situation.
</ul>

<p>The filename is where the template file lives on disk.  It can be
either an absolute filename, or relative to a directory in the
<A HREF="#search_path">template search path</A>.</p>

<p>In addition to reading a template from disk, it is possible to read
a template from a string, using <code>StringToTemplateCache()</code>.
The first argument of <code>StringToTemplateCache()</code> is a "key"
to use to refer to this string-based template.  This key takes the
place of the filename, for any routine that asks for a
filename + strip.</p>


<h3> <A NAME="expand_template">ExpandTemplate()</A> </h3>

<p>This is the main workhorse function of the template system.  It
takes the filename of a template, a <A
HREF="#template_dictionary">template dictionary</A>, and a string to
emit to, and emits an "expanded" version of the template using the
given template dictionary to fill in the template markers.</p>

<p>If the template specified by the given filename is already found in
an internal cache, the cached version of the template is used,
otherwise the template is loaded from disk, parsed, and stored in the
cache before expansion is performed.  As always, the "filename" can
also be a <A HREF="#strip">key</A> to a string-based template,
inserted directly into the cache via
<code>StringToTemplateCache()</code>.</p>

<p>There is an overloaded version of <code>Expand()</code> that takes
an <A HREF="#expand_emitter"><code>ExpandEmitter</code></A> rather
than a string, as the source to expand the template into.</p>

<p>This function returns true if the template was successfully
expanded into the output parameter.  It returns false if expansion
failed or was only partially successful.  It might fail because the
template file cannot be found on disk, or because the template has
syntax errors and cannot be parsed, or because the template
sub-includes another template, and that sub-template has errors.  To
minimize the risk of errors at expand-time, you can call
<code>LoadTemplate()</code> (below) first to load and parse the
template into the cache.  This will catch all errors except for errors
involving sub-templates.</p>

<p>In the case of partial failures -- typically, failures resulting in
an error in a sub-inclued template -- there may be partial data
emitted to the output before the error was detected.  If
<code>ExpandTemplate()</code> returns false, you should be careful to
check for and remove this partial data, if desired.</p>


<h3> <A NAME="expand_with_data">ExpandWithData()</A> </h3>

<p><code>ExpandWithData()</code> is like
<code>ExpandTemplate()</code>, with the addition that it allows you to
pass in <A HREF="#per_expand_data">per-expand data</A>.  It's called
like this:</p>
<pre>
   ctemplate::TemplateDictionary dict(...);
   ctemplate::PerExpandData per_expand_data;
   string output;
   ctemplate::ExpandWithData(filename, strip_mode, &amp;output, &amp;dict,
                             &amp;per_expand_data);
</pre>

<p>Per-expand data is applied to all templates that are seen while
expanding: not only the template you called <code>Expand()</code> on,
but also sub-templates that are brought in via template-includes
(<code>{{&gt;INCLUDE}}</code>).  See the description of the <A
HREF="#per_expand_data"><code>PerExpandData</code></A> class for more
details about how expansion can be modified by per-expand data.</p>

<p>The return value has the same meaning as for
<code>ExpandTemplate()</code> In fact, if you pass in
<code>NULL</code> as the <code>per_expand_data</code> argument, this
function is exactly equivalent to <code>ExpandTemplate()</code>.</p>


<h3> <A NAME="load_template">LoadTemplate()</A> </h3>

<p>This function takes a filename and a strip-mode, and loads the file
into the default template cache.  Future calls to
<code>ExpandTemplate()</code> or <code>ExpandWithData()</code> will
get the parsed template from the cache, without needing to go to
disk.</p>

<p>This function returns true if the template was successfully read
from disk, parsed, and inserted into the cache.  It will also return
true if the template is already in the cache (even if the file has
changed on disk since the template was inserted into the cache).  It
will return false if the file cannot be found on disk, or cannot be
successfully parsed.  (Note that <code>LoadTemplate()</code> cannot
detect errors in sub-included templates, since the identity of
sub-included templates is specified in a
<code>TemplateDictionary</code>, not in the template itself.)</p>


<h3> <A NAME="string_to_template_cache">StringToTemplateCache()</A> </h3>

<p>In addition to reading a template file from disk, it is also
possible to read a template file from a string, using
<code>StringToTemplateCache()</code>.  It takes the content
as a string.  It also takes in a key and a <A HREF="#strip">strip</A>
mode.  The given key and strip mode can be used as the filename/strip
pair in calls to <code>ExpandTemplate()</code> and similar
functions.  The key can also be used as the "filename" in calls to
<code>ctemplate::TemplateDictionary::SetFilename()</code>, allowing
this template to be included inside other templates.</p>

<p><code>StringToTemplateCache()</code> returns true if the string is
successfully inserted into the cache.  It returns false otherwise,
probably because there is already a string or filename in the cache
with the same key.</p>


<h3> default_template_cache() and mutable_default_template_cache() </h3>

<p>All the above routines -- <code>ExpandTemplate()</code>,
<code>LoadTemplate()</code>, and the like -- read and write parsed
templates to the default template cache.  This is just a static
instance of the <A
HREF="#template_cache"><code>TemplateCache</code></A> class.  It can
be accessed via these two functions:
<code>default_template_cache()</code> and, if you need a non-const
version of the cache, <code>mutable_default_template_cache()</code>.
These can be useful if you need the advanced features of template
caches, such as <code>ReloadAllIfChanged()</code> or
<code>ClearCache()</code>.</p>


<h2> <A NAME="template_dictionary">The <code>TemplateDictionary</code>
     Class</A> </h2>

<p>The class <code>TemplateDictionary</code> is used for all template
dictionary operations.  In general, an application will need to call a
<code>TemplateDictionary</code> method for every marker in the
associated template (the major exception: markers that evaluate to the
empty string can be ignored).</p>

<p>The appropriate function to call for a given template marker
depends on its type.</p>


<h3> Data Dictionaries </h3>

<p>A data dictionary is a map from keys to values.  The keys are
always strings, corresponding to the name of the associated template
marker, so a section <code>{{#FOO}}</code> in the template text is
matched to the key <code>FOO</code> in the dictionary, if it exists.
Note the case must match as well.</p>

<p>The value associated with a key differs according to key type.  The
value associated with a <i>variable</i> is simple: it's the value for
that variable.  Both keys and values can be any 8-bit
character-string, and may include internal NULs (<code>\0</code>).</p>

<p>The value associated with a <i>section</i> is a list of data
dictionaries.  At template-expansion time, the section is expanded
once for each dictionary in the list.  The first time, all
variables/etc. in the section will be evaluated taking into account
the first dictionary.  The second time, all variables/etc. will be
evaluated taking into account the second dictionary.  (See <A
HREF="#inheritance">below</A> for a definition of "taking into
account.")</p>

<p>The value associated with a <i>template-include</i> is also a list
of data dictionaries.  Each data dictionary in this list must also
have one other, mandatory associated piece of associated information:
the filename of the template to include.  At expand-time, that
filename is passed as-is to <code>ctemplate::ExpandTemplate()</code>
(or, more exactly, the equivalent of <code>ExpandTemplate()</code> in
the same <code>TemplateCache</code> that the parent template comes
from).</p>


<h3> <A NAME="inheritance">Details on Dictionary Lookup</A> </h3>

<p>The dictionary structure is a tree: there's a 'main' dictionary,
and then a list of sub-dictionaries for each section or
include-template.  When looking up a marker -- be it a variable,
section, or include-template marker -- the system looks in the
currently applicable dictionary.  If it's found there, that value is
used.  If not, and the parent dictionary is not an include-template,
it continues the look in the parent dictionary, and possibly the
grandparent, etc.  That is, lookup has <i>static scoping</i>: you look
in your dictionary and any parent dictionary that is associated with
the same template-file.  As soon as continuing the lookup would
require you to jump to a new template-file (which is what
include-template would do), we stop the lookup.</p>

<p>If lookup fails in all dictionaries, the template system does a
final lookup in the <b>global variable dictionary</b>.</p>

<p>The system initializes the global dictionary with a few useful
values for your convenience (the user can add more).  All system
variables are prefixed with <code>BI</code>, to emphasize they are
"built in" variables.</p>
<ul>
  <li> <code>BI_SPACE</code>, which has the value
       <code>&lt;space&gt;</code>.  It is used to force a space
       at the beginning or end of a line in the template,
       where it would normally be suppressed.  (See below.) </li>

  <li><code>BI_NEWLINE</code>, which has the value
       <code>&lt;newline&gt;</code> It is used to force a
       newline at the end of a line, where it would normally
       be suppressed.  (See below.) </li>
</ul>

<p>Variable inheritance happens at expand time, not at
dictionary-create time.  So if you create a section dictionary, and
then afterwards set a variable in its parent dictionary (or in the
global dictionary), the section <i>will</i> inherit that variable
value, if it doesn't define the value itself.</p>


<h3> SetValue() and variants </h3>

<p>SetValue() is used to set the value for a variable
marker in a dictionary.  It takes a string as input -- nominally a <A
HREF="#template_string"><code>TemplateString</code></A>, though a C++
string or C char* will be auto-converted -- for the variable name and
its value.  The name is the same string as is used for the variable's
template-marker inside the template this dictionary will be expanded
with: if the template reads <code>Hello {{NAME}}</code> then the
first argument to <code>SetValue()</code> must be <code>NAME</code>.
Case matters.</p>

<p><code>SetIntValue()</code> takes an integer as the value, rather
than a string.  On all platforms, the integer may be up to 64
bits.</p>

<p><code>SetFormattedValue()</code> is a convenience routine.
<code>SetFormattedValue(key, arg1, arg2, ...)</code> is logically
equivalent to</p>
<pre>
   char buffer[A_BIG_ENOUGH_NUMBER];
   sprintf(buffer, arg1, arg2, ...);
   SetValue(key, buffer);
</pre>
<p>without having to worry about the size of <code>buffer</code>, or
about stack overflow.</p>

<p><code>SetValueWithoutCopy()</code> is provided to give an extra bit
of efficiency when needed.  <code>SetValue()</code> will copy the key
and value into an internal data structure used by the
<code>TemplateDictionary</code>; this avoids dangling pointers if the
arguments to <code>SetValue()</code> are temporaries, or otherwise
have shorter lifetime than the <code>TemplateDictionary</code>.  But
if you know that both the key and value strings have lifetime longer
than the <code>TemplateDictionary</code> -- perhaps because they are
global (static duration) <code>char*</code>'s -- you can call
<code>SetValueWIthoutCopy()</code> to avoid the copy.  This yields a
small time savings at the cost of significant code fragility, so
should only be used when absolutely necessary.</p>


<h3> SetGlobalValue() and SetTemplateGlobalValue() </h3>

<p><code>SetGlobalValue()</code> is like <code>SetValue()</code> but
works on the global dictionary.  Since the global dictionary is shared
across all template dictionaries, this is a static method on
<code>TemplateDictionary</code>.  It is thread-safe.  It is also
relatively slow.</p>

<p><code>SetTemplateGlobalValue()</code> is like
<code>SetValue()</code>, but the values are preserved across
template-includes.</p>

<p>This example shows all three forms:</p>
<pre>
A.tpl:
   {{NAME}} has won {{>PRIZE}}.  It is worth {{AMOUNT}}.
B.tpl:
   {{AMOUNT}} dollars!  And it's all yours, {{NAME}}
C.tpl:
   To: {{NAME}}.  Amount: {{AMOUNT}}.
code:
   ctemplate::TemplateDictionary dict("set_value_demo");
   ctemplate::TemplateDictionary* subdict = dict.AddIncludeDictionary("PRIZE");
   subdict->SetFilename("B.tpl");
   dict->SetValue("NAME", "Jane McJane");
   dict->SetTemplateGlobalValue("AMOUNT", "One Million");
   ctemplate::TemplateDictionary::SetGlobalValue("NAME", "John Doe");
   ctemplate::TemplateDictionary dict_c("set_value_demo, part 2");

   ctemplate::ExpandTemplate("A.tpl", ..., &amp;dict);
   ctemplate::ExpandTemplate("C.tpl", ..., &amp;dict_c);
</pre>

<p>The first expand yields this:</p>
<pre>
   Jane McJane has won One Million dollars!  And it's all yours, John Doe.  It is worth One Million.
</pre>

<p>The second expand yields this:</p>
<pre>
   To: John Doe.  Amount: .
</pre>

<p><code>NAME</code> was set via <code>SetValue()</code>, so its
value was not propagated across the include-dict boundary; instead,
the subdict (B.tpl) got its value for <code>NAME</code> from the
global dictionary.  <code>AMOUNT</code>, on the other hand, was set
via <code>SetTemplateGlobalValue()</code>, so its value was propagated
across the boundary, and the subdict saw it.  However, the totally
unrelated template, C.tpl, did not see either value, and only sees the
values in the global dictionary.  (Of course, had we filled
<code>dict_c</code> with some values, C.tpl would have had access to
those.)</p>


<h3> AddSectionDictionary(), ShowSection(),
     and SetValueAndShowSection() </h3>

<p><code>AddSectionDictionary(section_name)</code> returns a
sub-dictionary associated with the given section_name (for instance,
<code>dict.AddSectionDictionary("MYSECT")</code> for a template like
<code>{{#MYSECT}}...{{/MYSECT}}</code>).  If called multiple times, it
will return a new dictionary each time.  During <code>Expand()</code>,
the section will be expanded once for each time
<code>AddSectionDictionary()</code> was called; that is, the text
inside the section delimiters will be repeated once for each
<code>AddSectionDictionary()</code> call, and within a single
repetition, the dictionary returned by
<code>AddSectionDictionary()</code> will be used to populate the text
inside the section delimiters.  (With the current dictionary as that
dictionary's parent, for inheritance purposes.)</p>

<p>This suggests that if <code>AddSectionDictionary()</code> is never
called on a section, the text inside the section will be omitted
entirely by <code>Expand()</code>.</p>

<p><code>ShowSection()</code> is a convenience method used to show the
text inside the section exactly once.  It is equivalent to calling
<code>AddSectionDictionary()</code> once, and ignoring the returned
sub-dictionary.  All variables in the section will depend on
dictionary inheritence to get their values.</p>

<p><code>SetValueAndShowSection()</code> is another convenience
method,, used to show a section if and only if a related variable is
set to a non-empty value.  <code>SetValueAndShowSection(name, value,
section_name)</code> is equivalent to this: if value is empty do
nothing, otherwise add a single dictionary to
<code>section_name</code> and call <code>section_dict->AddValue(name,
value)</code>.</p>

<p>Example:</p>
<pre>
   ctemplate::TemplateDictionary* dict = new ctemplate::TemplateDictionary("section example");
   const char* username = GetUsername();   // returns "" for no user
   if (username[0] != '\0') {
      ctemplate::TemplateDictionary* sub_dict = dict->AddSectionDictionary("CHANGE_USER");
      sub_dict->SetValue("USERNAME", username);
   } else {
      // don't need to do anything; we want a hidden section, which is the default
   }

   // Instead of the above 'if' statement, we could have done this:
   if (username[0] != '\0') {
      dict->ShowSection("CHANGE_USER");       // adds a single, empty dictionary
      dict->SetValue("USERNAME", username);   // take advantage of inheritance
   } else {
      // don't need to do anything; we want a hidden section, which is the default
   }

   // Or we could have done this:
   dict->SetValueAndShowSection("USERNAME", username, "CHANGE_USER");

   // Moving on...
   GetPrevSearches(prev_searches, &amp;num_prev_searches);
   if (num_prev_searches > 0) {
      for (int i = 0; i < num_prev_searches; ++i) {
         TemplateDictionary* sub_dict = dict->AddSectionDictionary("PREV_SEARCHES");
         sub_dict->SetValue("PREV_SEARCH", prev_searches[i]);
      }
   }
</pre>


<h3> AddIncludeDictionary() and SetFilename() </h3>

<p><code>AddIncludeDictionary(section_name)</code> returns a
sub-dictionary associated with the given include_name (for instance,
<code>dict.AddIncludeDictionary("MYTPL")</code> for a template like
<code>{{>MYTPL}}</code>).  If called multiple times, it
will return a new dictionary each time.  It is the responsibility of
the caller to then call <code>SetFilename()</code> on the
sub-dictionary returned.</p>

<p>During <code>Expand()</code>,
each dictionary returned by <code>AddIncludeDictionary</code> will be
examined in turn.  For each dictionary for which
<code>SetFilename()</code> is called, that filename will be read as a
template (via <code>LoadTemplate()</code>, with the same
"strip" value as the current template), and expanded using the
dictionary.  (Note that the dictionary will not inherit
<code>SetValue()</code> values from the parent dictionary, though it
will inherit <code>SetTemplateGlobalValue()</code> values.)  This
expanded template will then be emitted to the output.</p>

<p>Note that if <code>AddIncludeDictionary()</code> is never called,
the template-include will be a no-op during <code>Expand()</code>.
Likewise, if it is called but <code>SetFilename()</code> is never
called on the resulting sub-dictionary, the template-include will be a
no-op.  On the other hand, if it is called multiple times, multiple
templates -- possibly all from the same file, possibly not -- will be
inserted at the point of the template-include.</p>

<p>If a user has called <code>StringToTemplateCache(key, ...)</code>,
then the user can call <code>SetFilename(key)</code> to include the
contents of the string as the sub-template.</p>


<h3> Dump() and DumpToString() </h3>

<p>These routines dump the contents of a dictionary and its
sub-dictionaries.  <code>Dump()</code> dumps to stdout,
<code>DumpToString()</code> to a string.  They are intended for
debugging.</p>


<h2> <A NAME="template_cache">The <code>TemplateCache</code> Class</A> </h2>

<p>This class holds a collection of templates.  It can be used to give
you a coherent view of the template system: you load all the templates
you are going to use into the cache, and then reload them from disk in
one atomic operation.  You can have multiple
<code>TemplateCache</code> objects in your executable, perhaps one for
each service you provide, or perhaps one per thread (so as to avoid
thread contention when loading templates).</p>

<p>One intended use of the template cache is to make it safe to reload
template files while serving user requests from a webserver.  The idea
is that every user request, as it's created, is associated with the
current template cache.  When you wish to reload, you
<code>Clone()</code> the current cache, and then reload inside the
cloned copy.  New requests will get the cloned cache, while old
requests will continue to render using the old cache.
<code>TemplateCache</code> is written to make this use-case efficient:
templates are shared between caches when appropriate, with
reference-counting to keep memory management easy.</p>


<h3> The default template cache </h3>

<p>The template system creates a default template cache, which is
available via the functions <code>default_template_cache()</code> and
<code>mutable_default_template_cache()</code>.</p>

<p>For simple uses of the template system, using the default cache,
via <code>ExpandTemplate()</code> and the like, may be perfectly
adequate.  If you want more sophisticated features, such as the
ability to have different versions of the same template file active at
one time, or to change the template root-directory, you will have to
use an explicit <code>TemplateCache</code>.</p>


<h3> LoadTemplate() and StringToTemplateCache() </h3>

<p>These two routines are how you explicitly insert data into the
cache.  <code>LoadTemplate()</code> reads a template from disk, while
<code>StringToTemplateCache()</code> takes the data from a
user-specified string.  These work exactly the same as the global <A
HREF="#load_template"><code>LoadTemplate()</code></A> and <A
HREF="#string_to_template_cache"><code>StringToTemplateCache()</code></A>,
except they insert into the given <code>TemplateCache</code>, rather
than the global cache.</p>

<p><code>LoadTemplate()</code> is not strictly necessary: if the cache
cannot find a template it needs at <code>Expand*()</code> time, it will
automatically try to fetch it from disk.  It is intended mostly for
use with <A HREF="#freeze"><code>Freeze()</code></A>, which disables
this auto-fetch behavior.</p>

<p>Both of these routines take a <A HREF="#strip">strip</A> mode
specifying how the template system should treat whitespace while
parsing.</p>

<p>If the template-cache is <A HREF="#freeze">frozen</A>,
<code>LoadTemplate()</code> will only return true if the template is
already stored in the cache, and will return false in every other
case.  For a frozen cache, <code>StringToTemplateCache()</code> will
always return false.</p>


<h3> ExpandWithData() and ExpandFrozen() </h3>

<p>These routines takes a string that represents either a template
filename (for disk-based templates), or a key used in
<code>StringToTemplateCache()</code> (for string-based templates), a <A
HREF="#strip">strip</A> mode saying how to parse the template's
whitespace, and <A HREF="#per_expand_data">per-expand data</A> (which
can be NULL).  Overloads are provided to output the expanded template
to either a string or to an arbitrary <A
HREF="#expand_emitter"><code>ExpandEmitter</code></A>.</p>

<p>Expand uses the filename + strip pair to fetch the template from
the cache, if it's there.  If not, <code>ExpandWithData()</code> will
fetch the template from disk and insert it into the cache.
<code>ExpandFrozen()</code>, on the other hand, will just fail to
expand, and return false.  This is the only difference in behavior
between the two routines.  To reinforce this behavior,
<code>ExpandFrozen()</code> will return false immediately if <A
HREF="#freeze"><code>Freeze()</code></A> has not been called on the
cache.

<p>While expanding, the template system may come across template
sub-includes (<code>{{>SUB_TEMPLATE}}</code>).  It will attempt to
fetch these templates from the cache as well; failing that, it will
try to load the template from disk (for <code>ExpandWithData()</code>)
or else fail the expand and return false (for
<code>ExpandFrozen()</code>).</p>

<p>Because <code>ExpandFrozen()</code> never updates the cache, it is
a const method, unlike <code>ExpandWithData()</code>.</p>

<p>Note that <code>TemplateCache</code> does not provide the
convenience <code>ExpandTemplate()</code> routine, as the analogue of
the global <A
HREF="#expand_template"><code>ExpandTemplate()</code></A>.  If you are
not interested in the per-expand data, just call
<code>ExpandWithData()</code> with the per-expand data set to NULL.</p>


<h3> ReloadAllIfChanged() </h3>

<p>For every file-based template in the cache (this method ignores
string-based templates), <code>ReloadAllIfChanged()</code> checks the
filesystem to see if the file has changed since it was loaded into the
cache.  If so, the cache loads a new version of the file into the
cache.  Note that at this point both the old and new versions of the
file exist in the cache!  Only the new version is accessible via new
calls to <code>Expand()</code>, but any expansions currently in flight
during the <code>ReloadAllIfChanged()</code> call will continue to use
the old version.</p>

<p>NOTE: <code>ReloadAllIfChanged()</code> never modifies existing
items in the cache in any way.  It only loads new entries into the
cache.</p>

<p><code>ReloadAllIfChanged()</code> comes in two flavors, controlled
by the passed-in enum.  In "immediate" mode, it synchronously iterates
through the cache and reloads all files that need it.  In "lazy" mode,
it waits to reload a given template file until the next time it's
actually used (in a call to <code>Expand*()</code>).  "Immediate" mode
is safer in the case where templates depend on each other and the
files change a lot, since all files are reloaded at about the same
time.  "Lazy" mode avoids the latency spike of "immediate" mode, and
is preferable in the (common) case that files on disk change only
rarely.</p>


<h3> <A NAME="search_path"> SetTemplateRootDirectory(),
     AddAlternateTemplateRootDirectory(), and
     template_root_directory() </A> </h3>

<p>By default, filenames passed in to <code>Expand*()</code> are taken
to be relative to the current working directory.  These functions
change that behavior.  <code>SetTemplateRootDirectory()</code> resets
the search path to be the single path passed in to this function.
Every time <code>AddAlternateTemplateRootDirectory()</code> is called,
it adds another directory to the end of the search path.  The template
system will follow the search path, in order, when looking for a
filename.</p>

<p>Note that the template search path is only meaningful when the
filename passed to <code>Expand*()</code> (or specified for a
sub-include) is a relative filename.  If the filename is an absolute
filename, starting with <code>/</code>, the search path is
ignored.</p>

<p><code>template_root_directory()</code> returns the first entry in
the search path.  There is currently no way to access other entries in
the search path.</p>


<h3> FindTemplateFilename() </h3>

<p><code>FindTemplateFilename()</code> does the work of finding a
template file in the filesystem, using the current template search
path.  It takes a relative pathname as input, and returns an absolute
pathname as output, indicating where the template file lives on the
filesystem.  If the template file is not found, this method returns
the empty string.</p>


<h3> <A NAME="freeze">Freeze()</A> </h3>

<p><code>Freeze()</code> marks the template cache as immutable.  After
this method is called, the cache can no longer be modified by loading
new templates or reloading existing templates.  During expansion only
cached included templates will be used; they won't be loaded
on-demand.</p>

<p>Before calling <code>Freeze()</code>, you should make sure your
cache has all the templates it might need, using
<code>LoadTemplate()</code> and <code>StringToTemplateCache()</code>.
Otherwise, <code>ExpandWithData()</code> and
<code>ExpandFrozen()</code> may fail.</p>

<p>Once the cache is frozen, calls to
<code>SetTemplateRootDirectory()</code>,
<code>AddAlternateTemplateRootDirectory()</code>,
<code>Delete()</code>, and <code>ReloadAllIfChanged()</code> will
fail.</p>

<p>After the cache is frozen, the <code>TemplateCache</code> object is
effectively const.</p>


<h3> Delete() </h3>

<p>This method deletes an entry from the cache.  If the entry is in
the cache multiple times (each with a different "strip" mode), this
method deletes all of them.</p>


<h3> ClearCache() </h3>

<p>This method deletes all entries from the cache.  It can be called
even on a frozen cache.</p>

<p>Note: this method is not typically necessary unless you are testing
for memory leaks.  It is intended to be called just before exiting the
program, and after all template expansions are completed.  Using it in
that way may prevent unnecessary reporting by the leak checker.</p>


<h3> Clone() </h3>

<p><code>Clone()</code> makes a shallow copy of the given
<code>TemplateCache</code> object, and returns the copy.  The new copy
and the old share the same template objects; since it's a shallow
copy, they actually share pointers to the exact same object.  (Since
the template cache never changes a template object once it's loaded
into the cache, sharing the pointer isn't a risk.)</p>

<p>The intended use of <code>Clone()</code>, as described above, is to
allow fine control over "epochal" changes in templates.  One
<code>TemplateCache</code> can hold all versions of the template files
before the big update; after the update is done, you can clone the old
cache and then call <code>ReloadAllIfChanged()</code> on the clone.
This is a low-cost operation, since the two copies share most
resources.  Smart pointers take care of most memory management
issues.</p>

<p>The caller is responsible for calling <code>delete</code> on the
returned <code>TemplateCache</code> object.</p>



<h2> <A NAME="template_namelist">The <code>TemplateNamelist</code> Class</A> </h2>

<p>This class provides information about <A
HREF="guide.html#register">registered</A> templates.  Or more
precisely, all templates corresponding to registered filenames.</p>

<p>All methods in this class are static.</p>


<h3> RegisterTemplate() and
     RegisterTemplateFilename() </h3>

<p><code>TemplateNamelist::RegisterTemplate()</code> takes a filename
and adds it to the static namelist used by
<code>TemplateNamelist</code>.  All other methods of
<code>TemplateNamelist</code> work only on registered filenames.</p>

<p>It's fairly rare to call this method directly.  Instead, the more
common use is to use the macro <code>RegisterTemplateFilename</code>
somewhere in the global scope, like so:</p>
<pre>
RegisterTemplateFilename(EXAMPLE_FN, "example.tpl");
</pre>

<p>The reason to prefer the macro is it defines a global variable that
you can use instead of the hard-coded template name.  This helps catch
typos.  The <code>RegisterTemplateFilename()</code> example is
functionally equivalent to:</p>
<pre>
#define EXAMPLE_FN "example.tpl"
</pre>

<p>It can be used like this:</p>
<pre>
   ctemplate::ExpandTemplate(EXAMPLE_FN, ctemplate::DO_NOT_STRIP, ...);
</pre>


<h3> GetMissingList() </h3>

<p><code>TemplateNamelist::GetMissingList()</code> returns a list of
all registered templates (or rather, all filenames) where the file
could not be found on disk.</p>


<h3> AllDoExist() </h3>

<p>Returns true if and only if the missing-list is empty.</p>


<h3> GetBadSyntax() </h3>

<p>Returns a list of all registered templates where the template
contains a syntax error, and thus cannot be used.</p>


<h3> IsAllSyntaxOkay() </h3>

<p>True if and only if the bad-syntax list is empty.</p>


<h3> GetLastmodTime() </h3>

<p>Returns the latest last-modified time for any registered
template-file.</p>


<h2> <A NAME="template_modifier">The TemplateModifier Class</A>
     and Associated Functions</h2>

<p>A modifier is a filter that's applied at template-expand time, that
munges the value of the variable before it's output.  For instance,
<code>&lt;html&gt;&lt;body&gt;{{NAME:html_escape}}&lt;/body&gt;&lt;/html&gt;</code>
asks the template system to apply the built-in
<code>html_escape</code> modifier when expanding
<code>{{NAME}}</code>.  If you set <code>NAME</code> in your
dictionary to be <code>Jim &amp; Bob</code>, what will actually be
emitted in the template is <code>Jim &amp;amp; Bob</code>.</p>

<p>You can chain modifiers together.  This template first html-escapes
<code>NAME</code>, and then javascript-escapes that result:</p>
<pre>
   &lt;html&gt;&lt;body&gt;{{NAME:html_escape:javascript_escape}}&lt;/body&gt;&lt;/html&gt;
</pre>

<p>Modifiers typically have a long, descriptive name and also a
one-letter abbreviation.  So this example is equivalent to the
previous one:</p>
<pre>
   &lt;html&gt;&lt;body&gt;{{NAME:h:j}}&lt;/body&gt;&lt;/html&gt;
</pre>

<p>Some modifiers take an argument, specified after an equals
sign:</p>
<pre>
   &lt;html&gt;&lt;body&gt;{{NAME:html_escape_with_arg=pre}}&lt;/body&gt;&lt;/html&gt;
</pre>


<h3> Built-in Modifiers </h3>

<p>Here are the modifiers that are built in to the template system.
They are all defined in template_modifiers.cc:</p>

<table border="1" cellpadding="3" summary="List of built-in modifiers">
<tr><th>long name</th><th>short name</th><th>description</th></tr>

<tr><td><code>:cleanse_css</code></td><td><code>:c</code></td>
    <td>Removes characters not safe for a CSS value. Safe characters
      are alphanumeric, space, underscore, period, coma, exclamation
      mark, pound, percent, and dash.</td>
</tr>

<tr><td><code>:html_escape</code></td><td><code>:h</code></td>
    <td>html-escapes the variable before output
        (eg <code>&amp;</code> -> <code>&amp;amp;</code>)</td>
</tr>

<tr><td><code>:html_escape_with_arg</code></td><td><code>:H</code></td>
  <td>special purpose html escaping. See
    <a href="#html_escape_args">:H Arguments</a>
    below for details.</td>
</tr>

<tr><td><code>:img_src_url_escape_with_arg</code></td><td><code>:I</code></td>
    <td>special purpose image url escaping. See
      <a href="#url_escape_args">:I and :U Arguments</a>
      below for details.</td>
</tr>

<tr><td><code>:javascript_escape</code></td><td><code>:j</code></td>
    <td>javascript-escapes the variable before output (eg
        <code>&quot;</code> -> <code>\x27</code> and
        <code>&amp;</code> -> <code>\x26</code>)</td>
</tr>

<tr><td><code>:javascript_escape_with_arg</code></td><td><code>:J</code>
    </td>
    <td>special purpose javascript escaping. See
      <a href="#javascript_escape_args">:J Arguments</a>
      below for details.</td>
</tr>

<tr><td><code>:json_escape</code></td><td><code>:o</code></td>
    <td>json-escapes a variable before output as a string in json;
        HTML characters are escaped using Unicode escape sequences
        (e.g <code>&amp;</code> -> <code>\u0026</code>) to comply with
        <a href="http://www.ietf.org/rfc/rfc4627.txt">RFC 4627</a>.
    </td>
</tr>

<tr><td><code>:none</code></td><td></td>
    <td>leaves the variable as is (used to disable <A
    HREF="#auto_escape">auto-escaping</A>)</td>
</tr>

<tr><td><code>:pre_escape</code></td><td><code>:p</code></td>
    <td>pre-escapes the variable before output (same as html_escape but
      whitespace is preserved; useful for &lt;pre&gt;...&lt;/pre&gt;)</td>
</tr>

<tr><td><code>:url_escape_with_arg</code></td><td><code>:U</code></td>
    <td>special purpose url escaping. See
      <a href="#url_escape_args">:I and :U Arguments</a>
      below for details.</td>
</tr>

<tr><td><code>:url_query_escape</code></td><td><code>:u</code></td>
    <td>performs URL escaping on the variable before output.
        space is turned into +, and everything other than [0-9a-zA-Z.,_:*/~!()-], is
        transformed into %-style escapes.  Use this when you are building
        URLs with variables as parameters:
        <pre>&lt;a href="http://google.com/search?q={{QUERY:u}}"&gt;{{QUERY:h}}&lt;/a&gt;</pre>
    </td>
</tr>

<tr><td><code>:xml_escape</code></td><td></td>
    <td>xml-escapes the variable before output
        (the five characters <code>&lt;&gt;&amp;&quot;&#39;</code> become
        <code>&amp;lt&amp;gt;&amp;amp;&amp;quot;&amp;#39;</code>)
        suitable for content returned in raw XML. It is not intended
        for escaping content within CDATA blocks.</td>
</tr>

</table>

<p>The <code>*_with_arg</code> modifiers require an argument to
specify the type of escaping to use. The following sections list
the supported arguments for each of these modifiers.

<h4 id="html_escape_args">:H Arguments</h4>
<p>Here are the values that are supported by
the <code>html_escape_with_arg</code> modifier:</p>
<table border="1" cellpadding="3" summary="Arguments for :H modifier">
<tr><th>value</th><th>description</th></tr>

<tr><td><code>=snippet</code></td>
    <td>like <code>html_escape</code>, but allows HTML entities and
        some tags to pass through unchanged. The allowed tags
        are <code>&lt;br></code>, <code>&lt;wbr></code>, <code>&lt;b></code>,
        and <code>&lt;/b></code>.</td>
</tr>

<tr><td><code>=pre</code></td>
    <td>same as <code>pre_escape</code></td>
</tr>

<tr><td><code>=url</code></td>
    <td>same as <code>:U=html</code> below. For backwards compatibility.</td>
</tr>

<tr><td><code>=attribute</code></td>
    <td>replaces characters not safe for an use in an unquoted
        attribute with underscore. Safe characters are alphanumeric,
        underscore, dash, period, and colon.</td>
</tr>

</table>

<h4 id="url_escape_args">:I and :U Arguments</h4>
<p>Here are the values that are supported by
the <code>img_src_url_escape_with_arg</code> and
<code>url_escape_with_arg</code> modifiers:</p>
<table border="1" cellpadding="3" summary="Arguments for :I and :U modifiers">
<tr><th>value</th><th>description</th></tr>

<tr><td><code>=html</code></td>
    <td>Ensures that a variable contains a safe URL. Safe means that
        it is either a http or https URL, or else it has no protocol
        specified.
        <ul>
          <li>If the URL is safe, the modifier HTML-escapes the URL.
          <li>Otherwise, the modifier replaces the unsafe URL with one of the
          following values:
            <ul>
              <li><code>/images/cleardot.gif</code> (the <code>:I</code>
              modifier)
              <li><code>#</code> (the <code>:U</code> modifier)
            </ul>
          </li>
        </ul>
        <b>Do not use <code>:U</code> for image URLs.</b> Use <code>:I</code>
        instead.  <code>#</code> is not a safe replacement for an image URL.
        <code>&lt;img src=#&gt;</code> can cause each browser to request the
        entire page again.
    </td>
</tr>

<tr><td><code>=javascript</code></td>
    <td>Same as <code>=html</code>, but using javascript escaping
    instead of html escaping.</td>
</tr>

<tr><td><code>=css</code></td>
    <td>Same as <code>=html</code> but using CSS escaping instead
    of html escaping so that the variable can be safely inserted
    within a CSS <code>@import</code> statement or a CSS property.
    The characters in [\r\n()&#39;&quot;&lt;&gt;*\] are transformed
    into %-style escapes.</td>
</tr>

<tr><td><code>=query</code></td>
  <td>(Supported for <code>:U</code> only) Same as
    <code>url_query_escape</code>.</td>
</tr>

</table>

<h4 id="javascript_escape_args">:J Arguments</h4>
<p>Here are the values that are supported by
the <code>javascript_escape_with_arg</code> modifier:</p>
<table border="1" cellpadding="3" summary="Arguments for :J modifier">
<tr><th>value</th><th>description</th></tr>

<tr><td><code>=number</code></td>
    <td>Ensures that the variable is a valid number or boolean
        javascript literal. This includes booleans
        <code>true</code> and <code>false</code>, decimal
        numbers (e.g. <code>4.10</code> or <code>-5.01e+10</code>)
        as well as hex numbers (e.g. <code>0x5FF</code>). This modifier
        is intended to ensure the variable not enclosed in
        quotes cannot contain javascript code that may execute. It does
        not guarantee that the variable is syntactically well-formed.
        If the variable is safe, it is returned
        as-is, otherwise it is replaced with <code>null</code>.
        In the future we may add more logic to support objects and
        arrays.</td>
</tr>
</table>

<h3> Custom Modifiers </h3>

<p>In addition to the built-in modifiers, you can write your own
modifier.  Custom modifiers must have a name starting with "x-", and
the name can contain alphanumeric characters plus dashes and
underscores.  Custom modifiers can also accept values with any
character except for : and <code>}</code>.  For example
this template could be a valid use of a custom modifier:</p>

<pre>
{{VAR:x-my_modifier:value1,value2,value3 has spaces,etc}}
</pre>

<p>See <code>&lt;template_modifiers.h&gt;</code> for details on how to
write a modifier and how to register it.  In short, you write a
modifier by subclassing <code>ctemplate::TemplateModifier</code> and
overriding the <code>Modify</code> method, and you register it by
calling <code>ctemplate::AddModifier()</code>  Here is an example of
the code for a custom modifier:</p>
<pre>
   class StarEscape : public ctemplate::TemplateModifier {
     void Modify(const char* in, size_t inlen,
                 const ctemplate::PerExpandData* per_expand_data,
                 ctemplate::ExpandEmitter* outbuf, const string&amp; arg) const {
       outbuf->Emit(string("*") + string(in, inlen) + string("*"));
     }
   };
</pre>


<h3> Subclassing TemplateModifier </h3>

<p>The minimum work to create a custom modifier is to subclass
<code>TemplateModifier</code> and override the <code>Modify()</code>
method.  <code>Modify()</code> takes as input the value of the text to
be modified, as well as the <A HREF="#per_expand_data">per expand
data</A> associated with this <code>Expand()</code> call.  The method
may use this input, plus any other data it may have, to generate
output, which it should write into the given
<code>ExpandEmitter</code>.</p>

<p>The subclass can also override <code>MightModify()</code>.  This is
useful for modifiers that are typically a no-op (in which case the
modifier is just doing busy-work, copying its input to the output
<code>ExpandEmitter</code>).  If <code>MightModify()</code> returns
false, the template system will avoid calling <code>Modify()</code> at
all on that variable, avoiding the busy-work copy.</p>


<h3> AddModifier() </h3>

<p> AddModifier() is used to register a custom modifier,
so the modifier can be used in templates.  The name of the modifier
must start with <code>x-</code>. </p>


<h3> AddXssSafeModifier() </h3>

<p> <code>AddXssSafeModifier()</code> is used to register a custom
modifier that can work well with the <A
HREF="auto_escape.html">auto-escape system</A>.  It is used when the
modifier produces output that is "safe" from cross-site scripting
attacks in all contexts in which it might be used.  For instance, a
modifier that only emits numbers is xss-safe if it's only used in html
or javascript contexts.</p>


<h3> <A NAME="auto_escape">Auto-escaping and Manual Escaping</A> </h3>

<p>If the <A HREF="auto_escape.html">auto-escape pragma</A> is used
in a document, then all variables will be auto-escaped, even if
explicit modifiers are used on the variable.  The rules are a little
complicated:</p>

<ul>
  <li> If the explicit modifier is a built-in modifier, and that
       modifier is "compatible" with the modifier that auto-escape
       would perform ("compatible" means it safely escapes in at least
       as many contexts as the auto-escape modifier), then only the
       explicit modifier is applied, and no further auto-escaping is
       done. </li>

  <li> If the explicit modifier is a custom modifier registered using
       AddXssSafeModifier(), no further auto-escaping is
       done. </li>

  <li> If the explicit modifier is the :none modifier, no
       further auto-escaping is done.  This is the mechanism for
       manually turning off auto-escaping. </li>

  <li> In all other situations, auto-escaping will be performed after
       the explicit modifiers have all run. </li>
</ul>


<h2> <A NAME="per_expand_data">The <code>PerExpandData</code> Class</A> </h2>

<p><code>ExpandWithData()</code> and
<code>TemplateModifier::Modify()</code> both take a
<code>PerExpandData</code> object.  Per-expand data is applied to all
templates that are seen while expanding: not only the template you
called <code>ExpandWithData()</code> on, but also sub-templates that
are brought in via template-includes (<code>{{&gt;INCLUDE}}</code>).

<p>There are several types of per-expand data you can set, by calling
the appropriate method on a <code>PerExpandData</code> object.</p>


<h3> SetAnnotateOutput() </h3>

<p>This is a debugging function.  When expanding this template, it adds
marker-strings to the output to indicate what template-substitutions
the system made.  This takes a string argument which can be used to
shorten the filenames printed in the annotations: if the filename
contains the string you give, everything before that string is elided
from the filename before printing.  (It's safe to just always pass in
the empty string.)</p>


<h3> SetAnnotator() </h3>

<p>This overrides the default text-based annotation used by
<code>SetAnnotateOutput()</code>.  If this is set and
<code>SetAnnotateOutput()</code> is called, the per-expand data will
use this <A
HREF="#template_annotator"><code>TemplateAnnotator</code></A> instance
to do the annotation, rather than the default instance.</p>


<h3> InsertForModifiers() and LookupForModifiers() </h3>

<p><code>InsertForModifiers()</code> stores an arbitrary key/value
pair in the <code>PerExpandData</code> structure.  This is used with
<A HREF="#template_modifier">template modifiers</A>: the
<code>PerExpandData</code> object passed to
<code>ExpandWithData()</code> is made available to every template
modifier that is called during expand time (including any custom
modifiers).  The intended use of this functionality is to allow a
modifier to work one way when expanding a template with dictionary A,
and another way when expanding a template with dictionary B.  For
instance, a modifier might encrypt part of a webpage using a user's
secret-key, which is of course different for every expansion of the
webpage.</p>

<p><code>LookupForModifiers()</code> can be used by a
template-modifier to read the key/value pair inserted by
<code>InsertForModifiers()</code>.
<code>LookupForModifiersAsString()</code> is the same, but returns the
value as a char* rather than a void*, for convenience.</p>


<h3> SetTemplateExpansionModifier() </h3>

<p>This is an advanced feature for those who need a custom hook into
template expansion.  It will not be used by most programmers.  It
takes a template-modifier as its argument, but this template modifier
is treated specially: instead of applying when an appropriate magic
string appears in the text of a template, it applies every time a
template is expanded during a call to <code>ExpandWithData()</code>.
Note this means that it's called not only after the top-level
template, that <code>ExpandWithData()</code> is called on, is
expanded, but also on every sub-template that is expanded due to a
template-include.</p>

<p>This unusual functionality has a few unusual properties.  Since the
template expansion modifier is not called in normal fashion, the
normal <code>arg</code> argument to the template modifier does not
make sense.  Instead, the <code>arg</code> is set to the path of the
template which is being expanded.  Also, template expansion modifiers
can be expensive, since they are applied pretty indiscriminately, so
it can be worth implementing the <code>MightModifiy()</code> predicate
for the passed-in <code>TemplateModifier</code> to avoid unnecessary
work.</p>


<h2> <A NAME="template_annotator">The <code>TemplateAnnotator</code>
     Class</A> </h2>

<p>The <code>TemplateAnnotator</code> class is used to pass in to <A
HREF="#per_expand_data"><code>PerExpandData::SetAnnotator()</code></A>,
to control how expand-time annotation is done.  This is meant to be
used as a debugging routine.</p>

<p>This class is an abstract base class; <code>SetAnnotator()</code>
takes a subclass that implements the various methods of the base
class.  These methods control the action taken when various template
markers are seen during template expansion.</p>

<p><code>template_annotator.h</code> defines the abstract base class,
and also a concrete subclass that is used by default for annotation if
<code>SetAnnotator()</code> is not called.</p>


<h2> <A NAME="template_dictionary_peer">The
     <code>TemplateDictionaryPeer</code> Class</A> </h2>

<p>By design, it is not possible to view the contents of a
<code>TemplateDictionary</code>; we want to make sure the interface
between the logic layer of the application and the presentation layer
of the template goes in only one direction.  While generally this
keeps programs as clean as possible, it presents problems in testing
code, which may want to verify that a given
<code>TemplateDictionary</code> has been filled properly.  The
<code>TemplateDictionaryPeer</code> addresses this need.  It lives in
<code>template_test_util.h</code>.</p>

<p>Some of the methods of <code>TemplateDictionaryPeer</code> are
useful for internal tests only.  Below are some of the methods that
are most useful for user-level tests.</p>


<h3> STS_INIT_FOR_TEST </h3>

<p>This macro allows use of <code>STS_INIT</code> for testing, even
when the input pointer is not guaranteed to be allocated for the
entire length of the test (it must, of course, be allocated for the
entire lifetime of the template being tested).  Since normally
<code>STS_INIT</code> requires inputs to have static duration, this
allows for more flexibility in tests, at the cost of worse memory
management and decreased code safety (in that it's possible to
accidentally violate the lifetime requirements).</p>


<h3> GetSectionValue() </h3>

<p>This returns the value for the named variable.  It uses normal
template scoping rules to resolve the name.</p>


<h3> IsHiddenSection() and IsHiddenTemplate() </h3>

<p>Checks if a section or sub-template is "hidden" (that is, won't be
displayed at all).</p>


<h3> GetSectionDictionaries() and GetIncludeDictionaries() </h3>

<p>Returns all the sub-dictionaries for a given section or
template-include, in a vector.</>


<h3> Other Testing Functions </h3>

<p>template_test_util.h has other useful routines for
testing, such as ExpandIs(), which tests whether a
template + dictionary pair expands into an expected string.  See the
header file for details.</p>


<h2> <A NAME="expand_emitter">The <code>ExpandEmitter</code> Class</A> </h2>

<p>There are two overloads of <A
HREF="#expand_template"><code>ExpandTemplate()</code></A>: the first
emits the expanded template to a C++ string, and the second emits to
an <code>ExpandEmitter</code>: an abstract base class that serves as a
data source.  It supports just one overloaded method,
<code>Emit()</code>, that can take a char, a char*, or a C++ string as
input.</p>

<p>Using this class requires subclassing <code>ExpandEmitter</code>
and providing the various definitions for <code>Emit()</code>.  For
instance, a subclass might provide definitions of <code>Emit()</code>
that send the input bytes out to a network socket.</p>

<p>In addition to defining the abstract base class,
<code>template_emitter.h</code> provides a sample concrete subclass
implementation, for emitting to a string.</p>


<h2> <A NAME="template_string">The <code>TemplateString</code> and
     <code>StaticTemplateString</code> Classes</A> </h2>

<p><code>TemplateString</code> is a string-like implementation.
Ctemplate uses <code>TemplateString</code> almost exclusively,
internally.  Many of the public API methods, such as
<code>TemplateDictionary::SetValue()</code>, also take
<code>TemplateString</code> as input.  <code>TemplateString</code>
has implicit constructors for both C++ strings and char*'s, so every
method that takes a <code>TemplateString</code> will also work if
given a C++ string or a char*.  If you have a char* and know its
length, you can save a bit of work by explicitly constructing a
<code>TemplateString</code> with a char* + length, for instance:</p>
<pre>
   dict->SetValue(ctemplate::TemplateString("MYVAR", 5), value);
</pre>

<p>Some compile-time tools work with <code>TemplateString</code> to
offload computation from runtime to compile-time.  This is possible
because the Ctemplate code often stores a hash of a string
rather than a string directly.  For static, immutable strings,
<code>TemplateString</code> can store a pre-computed hash value.  This
functionality is used by <A
HREF="#make_tpl_varnames_h"><code>make_tpl_varnames_h</code></A>.  Thus,
using this tool to create constants to use for <code>SetValue()</code>
keys provides not only protection against typos, but a speed
improvement as well.</p>

<p>For immutable strings in your code, you can create efficient
compile-time template-string objects of your own -- in this case of
type <code>StaticTemplateString</code> -- by using the
<code>STS_INIT</code> macro, like so:</p>
<pre>
static const StaticTemplateString kSectName =
    STS_INIT(kSectName, "test_SetAddSectionDictionary");
</pre>

<p>The string variable's name, <code>kSectName</code> is repeated
twice.  The variable's value is specified inside the macro.  Note that
this macro should be used at the top level of a file, not inside
functions (even when the variables are made static), and you should
define the <code>StaticTemplateString</code> exactly as above:
<code>static const StaticTemplateString</code>.  Otherwise, the
undefined constructor/destructor order of C++ may result in surprising
behavior, wherein the <code>StaticTemplateString</code> is not
initialized when it ought to be.</p>


<h2> The <code>Template</code> Class </h2>

<p>In older version of ctemplate, the <code>Template</code> class,
which holds parsed templates, was a major part of the template
workflow: the common template use-case would be:</p>
<pre>
   Template* tpl = Template::GetTemplate(filename, strip_mode);
   TemplateDictionary dict(name);
   tpl->Expand(&amp;dict, &amp;outstring);
</pre>

<p>In current use, this model is deprecated in favor of the single
<code>ExpandTemplate()</code> call; support for <code>Template</code>
methods may be removed entirely in future versions of ctemplate.
However, you may still find older code using this old formulation.</p>


<h2> <A NAME="auto_escaping">Auto-Escaping</A> </h2>

<p>The <a href="auto_escape.html">Guide to using Auto Escape</a> has
an overview of Auto Escape as well as discussion of its limitations.
<!-- TODO(csilvers): move that information here? -->
To use it, put the following text at the top of the template:</p>
<pre>
  {{%AUTOESCAPE context="CONTEXT" [state="STATE"]}}
</pre>

<p>Description of the arguments:</p>
<ul>
  <li> The context attribute is one of <code>HTML</code>,
       <code>JAVASCRIPT</code>, <code>CSS</code>,
       <code>JSON</code> or <code>XML</code>. It must correspond
       to the context in which the browser will interpret this
       template. <b>Warning:</b> Setting the wrong context will
       result in wrong escaping applied to all variables in
       the given template. In particular, if the template starts with
       a <code>&lt;script&gt;</code> tag, its context is
       <code>HTML</code> and not <code>JAVASCRIPT</code>. Auto-Escape
       will recognize the <code>&lt;script&gt;</code> tag and hence
       properly Javascript-escape the variables within it. Similarly,
       if the template starts with a <code>&lt;style&gt;</code> tag,
       its context is <code>HTML</code> and not <code>CSS</code>.
</li>
  <li> The state attribute is commonly omitted.  It accepts the
       value <code>IN_TAG</code> in the <code>HTML</code> context
       to indicate that the template only contains (one or more)
       HTML attribute name and value pairs that are part of an
       HTML tag formed in a parent template.
</ul>

<p>This will auto-escape every variable in the template.  To turn off
auto-escaping for a particular variable, you can apply the
<code>none</code> modifier, like so: <code>{{MYVAR:none}}</code>.
Here is an example of an autoescaped document:</p>

<pre>
  {{%AUTOESCAPE context="HTML"}}

  &lt;body&gt;
    &lt;p&gt;Hello {{USER}}&lt;/p&gt;
    &lt;p&gt;&lt;a href="{{URL}}"&gt;Your Account&lt;/a&gt;&lt;/p&gt;
    &lt;p&gt;Your identifier: {{ID:none}}{{! This is dangerous! }}&lt;/p&gt;
  &lt;/body&gt;
</pre>


<h2> Development Tools </h2>

<p>This package includes several tools to make it easier to use write
and use templates.</p>


<h3> <A name="make_tpl_varnames_h">make_tpl_varnames_h:
     Template Syntax Checker and Header File Generator</A> </h3>

<p><code>make_tpl_varnames_h</code> is a "lint" style syntax checker
and header file generator.  It takes the names of template files as
command line arguments and loads each file into a Template object by
retrieving the file via the Template factory method.  The loading of
the file does pure syntax checking and reports such errors as
mis-matched section start/end markers, mis-matched open/close
double-curly braces, such as <code>"{{VAR}"</code>, or invalid
characters in template variables/names/comments.</p>

<p>If the template passes the syntax check, by default the utility
then creates a header file for use in the executable code that fills
the dictionary for the template.  If the developer includes this
header file, then constants in the header file may be referenced in
the dictionary building function, rather than hard-coding strings as
variable and section names.  By using these constants, the compiler
can notify the developer of spelling errors and mismatched names.
Here's an example of how this is used, and how it helps prevent
errors:</p>

<pre>
   const char * const kosr_RESULT_NUMBER = "RESULT_NUMBER";  // script output
   dict.SetValue("RESSULT_NUMBER", "4");    // typo is silently missed
   dict.SetValue(kosr_RESSULT_NUMBER, "4");   // compiler catches typo
</pre>

<p>Each constant is named as follows:</p>

<ul>
  <li> The initial letter 'k', indicating a defined constant. </li>

  <li> One or more prefix letters which are derived from the
       template file name.  These prefix letters consist of the first
       letter of the file name, followed by the first letter following
       each underscore in the name, with the exception of the letter
       'p' when it is followed by the letters "ost", as is a <A
       HREF="tips.html#versioning">recommended convention</A> for
       template versioning. For example, the prefix letters for the
       file <code>one_search_result_post20020815.tpl</code> are
       <code>osr</code>. </li>

  <li> An underscore. </li>

  <li> The variable or section name itself, same casing. </li>
</ul>

<p>As an example, the section name "RESULT_NUMBER" in the file
one_search_result_post20020815.tpl would be given the constant name
<code>kosr_RESULT_NUMBER</code> and would appear in the header file as
<code>const char * const kosr_RESULT_NUMBER = "RESULT_NUMBER";</code>
-- as in the example above.  (The variable is actually a
<code>StaticTemplateString</code>, not a char*, but the basic idea
holds.)</p>

<p>
An alternate output directory may be specified by the command line
flag <code>--header_dir</code>.
</p>

<p>The name of the generated header file is the same as the name of
the template file with an extension added to the name.  By default,
that extension is <code>.varnames.h</code>.  In the above example, the
header file containing the constant declarations would be named
<code>one_search_result_post20020815.tpl.varnames.h</code>. An
alternate extension may be provided via the command line flag
<code>--outputfile_suffix</code>.</p>

<p>Important command line flags:</p>

<ul>
  <li> <code>--noheader</code> -- Indicates that a header file
       should not be generated; only syntax checking should be done. </li>

  <li> <code>--header_dir</code> -- sets the directory where the header
       is written.  Default: "./" </li>

  <li> <code>--template_dir</code> -- sets the template root
       directory.  Default: <code>./</code> which is the correct
       specification when it is run from the directory where the templates
       are located.  This is only used if the input template filenames
       are specified as relative paths rather than absolute
       paths. </li>

  <li> <code>--outputfile_suffix</code> -- the extension added to the
       name of the template file to create the name of the generated
       header file.  Default: <code>.varnames.h</code>.
</ul>

<p>For a full list of command line flags, run
<code>make_tpl_varnames_h --help</code>.</p>


<h3> <A name="template_converter">template-converter: convert a
     template to a C++ string</A> </h3>

<p><code>StringToTemplateCache()</code> lets you load a template
from a string instead of a file.  Applications may prefer this option
to reduce the dependencies of the executable, or use it in
environments where data files are not practical.  In such cases,
<code>template-converter</code> can be used as a template "compiler",
letting the developer write a template file as a data file in the
normal way, and then "compiling" it to a C++ string to be included in
the executable.</p>

<p>Usage is <code>template-converter &lt;template filename&gt;</code>.
C++ code is output is to stdout; it can be stored in a .h file or
included directly into a C++ file.  Perl must be installed to use this
script.</p>


<hr>
<ul>
  <li> <A HREF="guide.html">User's Guide</A> </li>
<!--
  <li> <A HREF="reference.html">Reference Manual</A> </li>
-->
  <li> <A HREF="auto_escape.html">Auto Escape</A> </li>
  <li> <A HREF="tips.html">Tips</A> </li>
  <li> <A HREF="example.html">Example</A> </li>
</ul>

<hr>
<address>
Craig Silverstein<br>
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</address>

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