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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Coding Guidelines</title>
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"Modular DocBook HTML Stylesheet Version 1.79">
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"#840084" alink="#0000FF">
<div class="NAVHEADER">
<table summary="Header navigation table" width="100%" border="0"
cellpadding="0" cellspacing="0">
<tr>
<th colspan="3" align="center">Privoxy Developer Manual</th>
</tr>
<tr>
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"documentation.html" accesskey="P">Prev</a></td>
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accesskey="N">Next</a></td>
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</table>
<hr align="left" width="100%">
</div>
<div class="SECT1">
<h1 class="SECT1"><a name="CODING" id="CODING">4. Coding
Guidelines</a></h1>
<div class="SECT2">
<h2 class="SECT2"><a name="S1" id="S1">4.1. Introduction</a></h2>
<p>This set of standards is designed to make our lives easier. It is
developed with the simple goal of helping us keep the "new and improved
<span class="APPLICATION">Privoxy</span>" consistent and reliable. Thus
making maintenance easier and increasing chances of success of the
project.</p>
<p>And that of course comes back to us as individuals. If we can
increase our development and product efficiencies then we can solve
more of the request for changes/improvements and in general feel good
about ourselves. ;-></p>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S2" id="S2">4.2. Using Comments</a></h2>
<div class="SECT3">
<h3 class="SECT3"><a name="S3" id="S3">4.2.1. Comment, Comment,
Comment</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Comment as much as possible without commenting the obvious. For
example do not comment "variable_a is equal to variable_b". Instead
explain why variable_a should be equal to the variable_b. Just
because a person can read code does not mean they will understand why
or what is being done. A reader may spend a lot more time figuring
out what is going on when a simple comment or explanation would have
prevented the extra research. Please help your fellow Privoxy
developers out!</p>
<p>The comments will also help justify the intent of the code. If the
comment describes something different than what the code is doing
then maybe a programming error is occurring.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
/* if page size greater than 1k ... */
if (page_length() > 1024)
{
... "block" the page up ...
}
/* if page size is small, send it in blocks */
if (page_length() > 1024)
{
... "block" the page up ...
}
This demonstrates 2 cases of "what not to do". The first is a
"syntax comment". The second is a comment that does not fit what
is actually being done.
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S4" id="S4">4.2.2. Use blocks for
comments</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Comments can help or they can clutter. They help when they are
differentiated from the code they describe. One line comments do not
offer effective separation between the comment and the code. Block
identifiers do, by surrounding the code with a clear, definable
pattern.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
/*********************************************************************
* This will stand out clearly in your code!
*********************************************************************/
if (this_variable == that_variable)
{
do_something_very_important();
}
/* unfortunately, this may not */
if (this_variable == that_variable)
{
do_something_very_important();
}
if (this_variable == that_variable) /* this may not either */
{
do_something_very_important();
}
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class=
"EMPHASIS">Exception:</i></span></p>
<p>If you are trying to add a small logic comment and do not wish to
"disrupt" the flow of the code, feel free to use a 1 line comment
which is NOT on the same line as the code.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S5" id="S5">4.2.3. Keep Comments on their
own line</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>It goes back to the question of readability. If the comment is on
the same line as the code it will be harder to read than the comment
that is on its own line.</p>
<p>There are three exceptions to this rule, which should be violated
freely and often: during the definition of variables, at the end of
closing braces, when used to comment parameters.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
/*********************************************************************
* This will stand out clearly in your code,
* But the second example won't.
*********************************************************************/
if (this_variable == this_variable)
{
do_something_very_important();
}
if (this_variable == this_variable) /*can you see me?*/
{
do_something_very_important(); /*not easily*/
}
/*********************************************************************
* But, the encouraged exceptions:
*********************************************************************/
int urls_read = 0; /* # of urls read + rejected */
int urls_rejected = 0; /* # of urls rejected */
if (1 == X)
{
do_something_very_important();
}
short do_something_very_important(
short firstparam, /* represents something */
short nextparam /* represents something else */ )
{
...code here...
} /* -END- do_something_very_important */
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S6" id="S6">4.2.4. Comment each logical
step</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Logical steps should be commented to help others follow the intent
of the written code and comments will make the code more
readable.</p>
<p>If you have 25 lines of code without a comment, you should
probably go back into it to see where you forgot to put one.</p>
<p>Most "for", "while", "do", etc... loops _probably_ need a comment.
After all, these are usually major logic containers.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S7" id="S7">4.2.5. Comment All Functions
Thoroughly</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>A reader of the code should be able to look at the comments just
prior to the beginning of a function and discern the reason for its
existence and the consequences of using it. The reader should not
have to read through the code to determine if a given function is
safe for a desired use. The proper information thoroughly presented
at the introduction of a function not only saves time for subsequent
maintenance or debugging, it more importantly aids in code reuse by
allowing a user to determine the safety and applicability of any
function for the problem at hand. As a result of such benefits, all
functions should contain the information presented in the addendum
section of this document.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S8" id="S8">4.2.6. Comment at the end of
braces if the content is more than one screen length</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Each closing brace should be followed on the same line by a
comment that describes the origination of the brace if the original
brace is off of the screen, or otherwise far away from the closing
brace. This will simplify the debugging, maintenance, and readability
of the code.</p>
<p>As a suggestion , use the following flags to make the comment and
its brace more readable:</p>
<p>use following a closing brace: } /* -END- if() or while () or
etc... */</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
if (1 == X)
{
do_something_very_important();
...some long list of commands...
} /* -END- if x is 1 */
or:
if (1 == X)
{
do_something_very_important();
...some long list of commands...
} /* -END- if (1 == X) */
</pre>
</td>
</tr>
</table>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S9" id="S9">4.3. Naming Conventions</a></h2>
<div class="SECT3">
<h3 class="SECT3"><a name="S10" id="S10">4.3.1. Variable
Names</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Use all lowercase, and separate words via an underscore ('_'). Do
not start an identifier with an underscore. (ANSI C reserves these
for use by the compiler and system headers.) Do not use identifiers
which are reserved in ANSI C++. (E.g. template, class, true, false,
...). This is in case we ever decide to port Privoxy to C++.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int ms_iis5_hack = 0;
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int msiis5hack = 0; int msIis5Hack = 0;
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S11" id="S11">4.3.2. Function
Names</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Use all lowercase, and separate words via an underscore ('_'). Do
not start an identifier with an underscore. (ANSI C reserves these
for use by the compiler and system headers.) Do not use identifiers
which are reserved in ANSI C++. (E.g. template, class, true, false,
...). This is in case we ever decide to port Privoxy to C++.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int load_some_file(struct client_state *csp)
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int loadsomefile(struct client_state *csp)
int loadSomeFile(struct client_state *csp)
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S12" id="S12">4.3.3. Header file
prototypes</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Use a descriptive parameter name in the function prototype in
header files. Use the same parameter name in the header file that you
use in the c file.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
(.h) extern int load_aclfile(struct client_state *csp);
(.c) int load_aclfile(struct client_state *csp)
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
(.h) extern int load_aclfile(struct client_state *); or
(.h) extern int load_aclfile();
(.c) int load_aclfile(struct client_state *csp)
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S13" id="S13">4.3.4. Enumerations, and
#defines</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Use all capital letters, with underscores between words. Do not
start an identifier with an underscore. (ANSI C reserves these for
use by the compiler and system headers.)</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
(enumeration) : enum Boolean {FALSE, TRUE};
(#define) : #define DEFAULT_SIZE 100;
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> We
have a standard naming scheme for #defines that toggle a feature in
the preprocessor: FEATURE_>, where > is a short (preferably 1
or 2 word) description.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#define FEATURE_FORCE 1
#ifdef FEATURE_FORCE
#define FORCE_PREFIX blah
#endif /* def FEATURE_FORCE */
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S14" id="S14">4.3.5. Constants</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Spell common words out entirely (do not remove vowels).</p>
<p>Use only widely-known domain acronyms and abbreviations.
Capitalize all letters of an acronym.</p>
<p>Use underscore (_) to separate adjacent acronyms and
abbreviations. Never terminate a name with an underscore.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#define USE_IMAGE_LIST 1
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#define USE_IMG_LST 1 or
#define _USE_IMAGE_LIST 1 or
#define USE_IMAGE_LIST_ 1 or
#define use_image_list 1 or
#define UseImageList 1
</pre>
</td>
</tr>
</table>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S15" id="S15">4.4. Using Space</a></h2>
<div class="SECT3">
<h3 class="SECT3"><a name="S16" id="S16">4.4.1. Put braces on a line
by themselves.</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>The brace needs to be on a line all by itself, not at the end of
the statement. Curly braces should line up with the construct that
they're associated with. This practice makes it easier to identify
the opening and closing braces for a block.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
if (this == that)
{
...
}
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<p>if (this == that) { ... }</p>
<p>or</p>
<p>if (this == that) { ... }</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> In the
special case that the if-statement is inside a loop, and it is
trivial, i.e. it tests for a condition that is obvious from the
purpose of the block, one-liners as above may optically preserve the
loop structure and make it easier to read.</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span>
developer-discretion.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example
exception:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
while (more lines are read)
{
/* Please document what is/is not a comment line here */
if (it's a comment) continue;
do_something(line);
}
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S17" id="S17">4.4.2. ALL control
statements should have a block</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Using braces to make a block will make your code more readable and
less prone to error. All control statements should have a block
defined.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
if (this == that)
{
do_something();
do_something_else();
}
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<p>if (this == that) do_something(); do_something_else();</p>
<p>or</p>
<p>if (this == that) do_something();</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> The
first example in "Instead of" will execute in a manner other than
that which the developer desired (per indentation). Using code braces
would have prevented this "feature". The "explanation" and
"exception" from the point above also applies.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S18" id="S18">4.4.3. Do not
belabor/blow-up boolean expressions</a></h3>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
structure->flag = (condition);
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<p>if (condition) { structure->flag = 1; } else {
structure->flag = 0; }</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> The
former is readable and concise. The later is wordy and inefficient.
Please assume that any developer new to the project has at least a
"good" knowledge of C/C++. (Hope I do not offend by that last comment
... 8-)</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S19" id="S19">4.4.4. Use white space
freely because it is free</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Make it readable. The notable exception to using white space
freely is listed in the next guideline.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int first_value = 0;
int some_value = 0;
int another_value = 0;
int this_variable = 0;
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S20" id="S20">4.4.5. Don't use white space
around structure operators</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>- structure pointer operator ( "->" ) - member operator ( "." )
- functions and parentheses</p>
<p>It is a general coding practice to put pointers, references, and
function parentheses next to names. With spaces, the connection
between the object and variable/function name is not as clear.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
a_struct->a_member;
a_struct.a_member;
function_name();
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead of:</i></span>
a_struct -> a_member; a_struct . a_member; function_name ();</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S21" id="S21">4.4.6. Make the last brace
of a function stand out</a></h3>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int function1( ... )
{
...code...
return(ret_code);
} /* -END- function1 */
int function2( ... )
{
} /* -END- function2 */
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<p>int function1( ... ) { ...code... return(ret_code); } int
function2( ... ) { }</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> Use 1
blank line before the closing brace and 2 lines afterward. This makes
the end of function standout to the most casual viewer. Although
function comments help separate functions, this is still a good
coding practice. In fact, I follow these rules when using blocks in
"for", "while", "do" loops, and long if {} statements too. After all
whitespace is free!</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span>
developer-discretion on the number of blank lines. Enforced is the
end of function comments.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S22" id="S22">4.4.7. Use 3 character
indentions</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>If some use 8 character TABs and some use 3 character TABs, the
code can look *very* ragged. So use 3 character indentions only. If
you like to use TABs, pass your code through a filter such as "expand
-t3" before checking in your code.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
static const char * const url_code_map[256] =
{
NULL, ...
};
int function1( ... )
{
if (1)
{
return ALWAYS_TRUE;
}
else
{
return HOW_DID_YOU_GET_HERE;
}
return NEVER_GETS_HERE;
}
</pre>
</td>
</tr>
</table>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S23" id="S23">4.5. Initializing</a></h2>
<div class="SECT3">
<h3 class="SECT3"><a name="S24" id="S24">4.5.1. Initialize all
variables</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Do not assume that the variables declared will not be used until
after they have been assigned a value somewhere else in the code.
Remove the chance of accidentally using an unassigned variable.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
short a_short = 0;
float a_float = 0;
struct *ptr = NULL;
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> It is
much easier to debug a SIGSEGV if the message says you are trying to
access memory address 00000000 and not 129FA012; or array_ptr[20]
causes a SIGSEV vs. array_ptr[0].</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span>
developer-discretion if and only if the variable is assigned a value
"shortly after" declaration.</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S25" id="S25">4.6. Functions</a></h2>
<div class="SECT3">
<h3 class="SECT3"><a name="S26" id="S26">4.6.1. Name functions that
return a boolean as a question.</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Value should be phrased as a question that would logically be
answered as a true or false statement</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
should_we_block_this();
contains_an_image();
is_web_page_blank();
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S27" id="S27">4.6.2. Always specify a
return type for a function.</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>The default return for a function is an int. To avoid ambiguity,
create a return for a function when the return has a purpose, and
create a void return type if the function does not need to return
anything.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S28" id="S28">4.6.3. Minimize function
calls when iterating by using variables</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>It is easy to write the following code, and a clear argument can
be made that the code is easy to understand:</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
for (size_t cnt = 0; cnt < block_list_length(); cnt++)
{
....
}
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span>
Unfortunately, this makes a function call for each and every
iteration. This increases the overhead in the program, because the
compiler has to look up the function each time, call it, and return a
value. Depending on what occurs in the block_list_length() call, it
might even be creating and destroying structures with each iteration,
even though in each case it is comparing "cnt" to the same value,
over and over. Remember too - even a call to block_list_length() is a
function call, with the same overhead.</p>
<p>Instead of using a function call during the iterations, assign the
value to a variable, and evaluate using the variable.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
size_t len = block_list_length();
for (size_t cnt = 0; cnt < len; cnt++)
{
....
}
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Exceptions:</i></span>
if the value of block_list_length() *may* change or could
*potentially* change, then you must code the function call in the
for/while loop.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S29" id="S29">4.6.4. Pass and Return by
Const Reference</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>This allows a developer to define a const pointer and call your
function. If your function does not have the const keyword, we may
not be able to use your function. Consider strcmp, if it were defined
as: extern int strcmp(char *s1, char *s2);</p>
<p>I could then not use it to compare argv's in main: int main(int
argc, const char *argv[]) { strcmp(argv[0], "privoxy"); }</p>
<p>Both these pointers are *const*! If the c runtime library
maintainers do it, we should too.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S30" id="S30">4.6.5. Pass and Return by
Value</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Most structures cannot fit onto a normal stack entry (i.e. they
are not 4 bytes or less). Aka, a function declaration like: int
load_aclfile(struct client_state csp)</p>
<p>would not work. So, to be consistent, we should declare all
prototypes with "pass by value": int load_aclfile(struct client_state
*csp)</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S31" id="S31">4.6.6. Names of include
files</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Your include statements should contain the file name without a
path. The path should be listed in the Makefile, using -I as
processor directive to search the indicated paths. An exception to
this would be for some proprietary software that utilizes a partial
path to distinguish their header files from system or other header
files.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#include <iostream.h> /* This is not a local include */
#include "config.h" /* This IS a local include */
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class=
"EMPHASIS">Exception:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
/* This is not a local include, but requires a path element. */
#include <sys/fileName.h>
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span>
Please! do not add "-I." to the Makefile without a _very_ good
reason. This duplicates the #include "file.h" behavior.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S32" id="S32">4.6.7. Provide multiple
inclusion protection</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Prevents compiler and linker errors resulting from redefinition of
items.</p>
<p>Wrap each header file with the following syntax to prevent
multiple inclusions of the file. Of course, replace PROJECT_H with
your file name, with "." Changed to "_", and make it uppercase.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#ifndef PROJECT_H_INCLUDED
#define PROJECT_H_INCLUDED
...
#endif /* ndef PROJECT_H_INCLUDED */
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S33" id="S33">4.6.8. Use `extern "C"` when
appropriate</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>If our headers are included from C++, they must declare our
functions as `extern "C"`. This has no cost in C, but increases the
potential re-usability of our code.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#ifdef __cplusplus
extern "C"
{
#endif /* def __cplusplus */
... function definitions here ...
#ifdef __cplusplus
}
#endif /* def __cplusplus */
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S34" id="S34">4.6.9. Where Possible, Use
Forward Struct Declaration Instead of Includes</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Useful in headers that include pointers to other struct's.
Modifications to excess header files may cause needless compiles.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
/*********************************************************************
* We're avoiding an include statement here!
*********************************************************************/
struct file_list;
extern file_list *xyz;
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> If you
declare "file_list xyz;" (without the pointer), then including the
proper header file is necessary. If you only want to prototype a
pointer, however, the header file is unnecessary.</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span> Use
with discretion.</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S35" id="S35">4.7. General Coding
Practices</a></h2>
<div class="SECT3">
<h3 class="SECT3"><a name="S36" id="S36">4.7.1. Turn on
warnings</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation</i></span></p>
<p>Compiler warnings are meant to help you find bugs. You should turn
on as many as possible. With GCC, the switch is "-Wall". Try and fix
as many warnings as possible.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S37" id="S37">4.7.2. Provide a default
case for all switch statements</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>What you think is guaranteed is never really guaranteed. The value
that you don't think you need to check is the one that someday will
be passed. So, to protect yourself from the unknown, always have a
default step in a switch statement.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
switch (hash_string(cmd))
{
case hash_actions_file:
... code ...
break;
case hash_confdir:
... code ...
break;
default:
log_error( ... );
... anomaly code goes here ...
continue; / break; / exit( 1 ); / etc ...
} /* end switch (hash_string(cmd)) */
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> If you
already have a default condition, you are obviously exempt from this
point. Of note, most of the WIN32 code calls `DefWindowProc' after
the switch statement. This API call *should* be included in a default
statement.</p>
<p><span class="emphasis"><i class="EMPHASIS">Another
Note:</i></span> This is not so much a readability issue as a robust
programming issue. The "anomaly code goes here" may be no more than a
print to the STDERR stream (as in load_config). Or it may really be
an abort condition.</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span>
Programmer discretion is advised.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S38" id="S38">4.7.3. Try to avoid falling
through cases in a switch statement.</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>In general, you will want to have a 'break' statement within each
'case' of a switch statement. This allows for the code to be more
readable and understandable, and furthermore can prevent unwanted
surprises if someone else later gets creative and moves the code
around.</p>
<p>The language allows you to plan the fall through from one case
statement to another simply by omitting the break statement within
the case statement. This feature does have benefits, but should only
be used in rare cases. In general, use a break statement for each
case statement.</p>
<p>If you choose to allow fall through, you should comment both the
fact of the fall through and reason why you felt it was
necessary.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S40" id="S40">4.7.4. Don't mix size_t and
other types</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>The type of size_t varies across platforms. Do not make
assumptions about whether it is signed or unsigned, or about how long
it is. Do not compare a size_t against another variable of a
different type (or even against a constant) without casting one of
the values.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S41" id="S41">4.7.5. Declare each variable
and struct on its own line.</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>It can be tempting to declare a series of variables all on one
line. Don't.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
long a = 0;
long b = 0;
long c = 0;
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Instead
of:</i></span></p>
<p>long a, b, c;</p>
<p><span class="emphasis"><i class="EMPHASIS">Explanation:</i></span>
- there is more room for comments on the individual variables -
easier to add new variables without messing up the original ones -
when searching on a variable to find its type, there is less clutter
to "visually" eliminate</p>
<p><span class="emphasis"><i class="EMPHASIS">Exceptions:</i></span>
when you want to declare a bunch of loop variables or other trivial
variables; feel free to declare them on one line. You should,
although, provide a good comment on their functions.</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span>
developer-discretion.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S42" id="S42">4.7.6. Use malloc/zalloc
sparingly</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>Create a local struct (on the stack) if the variable will live and
die within the context of one function call.</p>
<p>Only "malloc" a struct (on the heap) if the variable's life will
extend beyond the context of one function call.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
If a function creates a struct and stores a pointer to it in a
list, then it should definitely be allocated via `malloc'.
</pre>
</td>
</tr>
</table>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S43" id="S43">4.7.7. The Programmer Who
Uses 'malloc' is Responsible for Ensuring 'free'</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>If you have to "malloc" an instance, you are responsible for
insuring that the instance is `free'd, even if the deallocation event
falls within some other programmer's code. You are also responsible
for ensuring that deletion is timely (i.e. not too soon, not too
late). This is known as "low-coupling" and is a "good thing (tm)".
You may need to offer a free/unload/destructor type function to
accommodate this.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
int load_re_filterfile(struct client_state *csp) { ... }
static void unload_re_filterfile(void *f) { ... }
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class=
"EMPHASIS">Exceptions:</i></span></p>
<p>The developer cannot be expected to provide `free'ing functions
for C run-time library functions ... such as `strdup'.</p>
<p><span class="emphasis"><i class="EMPHASIS">Status:</i></span>
developer-discretion. The "main" use of this standard is for
allocating and freeing data structures (complex or nested).</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S44" id="S44">4.7.8. Add loaders to the
`file_list' structure and in order</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>I have ordered all of the "blocker" file code to be in alpha
order. It is easier to add/read new blockers when you expect a
certain order.</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> It may
appear that the alpha order is broken in places by POPUP tests coming
before PCRS tests. But since POPUPs can also be referred to as
KILLPOPUPs, it is clear that it should come first.</p>
</div>
<div class="SECT3">
<h3 class="SECT3"><a name="S45" id="S45">4.7.9. "Uncertain" new code
and/or changes to existing code, use XXX</a></h3>
<p><span class="emphasis"><i class=
"EMPHASIS">Explanation:</i></span></p>
<p>If you have enough confidence in new code or confidence in your
changes, but are not *quite* sure of the repercussions, add this:</p>
<p>/* XXX: this code has a logic error on platform XYZ, * attempting
to fix */ #ifdef PLATFORM ...changed code here... #endif</p>
<p>or:</p>
<p>/* XXX: I think the original author really meant this... */
...changed code here...</p>
<p>or:</p>
<p>/* XXX: new code that *may* break something else... */ ...new code
here...</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> If you
make it clear that this may or may not be a "good thing (tm)", it
will be easier to identify and include in the project (or conversely
exclude from the project).</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2"><a name="S46" id="S46">4.8. Addendum: Template for
files and function comment blocks:</a></h2>
<p><span class="emphasis"><i class="EMPHASIS">Example for file
comments:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
const char FILENAME_rcs[] = "$I<!-- Break CVS Substitution -->d$";
/*********************************************************************
*
* File : $S<!-- Break CVS Substitution -->ource$
*
* Purpose : (Fill me in with a good description!)
*
* Copyright : Written by and Copyright (C) 2001-2009
* the Privoxy team. http://www.privoxy.org/
*
* This program is free software; you can redistribute it
* and/or modify it under the terms of the GNU General
* Public License as published by the Free Software
* Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will
* be useful, but WITHOUT ANY WARRANTY; without even the
* implied warranty of MERCHANTABILITY or FITNESS FOR A
* PARTICULAR PURPOSE. See the GNU General Public
* License for more details.
*
* The GNU General Public License should be included with
* this file. If not, you can view it at
* http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
* or write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 ,
* USA
*
*********************************************************************/
#include "config.h"
...necessary include files for us to do our work...
const char FILENAME_h_rcs[] = FILENAME_H_VERSION;
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> This
declares the rcs variables that should be added to the
"show-proxy-args" page. If this is a brand new creation by you, you are
free to change the "Copyright" section to represent the rights you wish
to maintain.</p>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> The
formfeed character that is present right after the comment flower box
is handy for (X|GNU)Emacs users to skip the verbiage and get to the
heart of the code (via `forward-page' and `backward-page'). Please
include it if you can.</p>
<p><span class="emphasis"><i class="EMPHASIS">Example for file header
comments:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
#ifndef _FILENAME_H
#define _FILENAME_H
#define FILENAME_H_VERSION "$I<!-- Break CVS Substitution -->d$"
/*********************************************************************
*
* File : $S<!-- Break CVS Substitution -->ource$
*
* Purpose : (Fill me in with a good description!)
*
* Copyright : Written by and Copyright (C) 2001-2009
* the Privoxy team. http://www.privoxy.org/
*
* This program is free software; you can redistribute it
* and/or modify it under the terms of the GNU General
* Public License as published by the Free Software
* Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will
* be useful, but WITHOUT ANY WARRANTY; without even the
* implied warranty of MERCHANTABILITY or FITNESS FOR A
* PARTICULAR PURPOSE. See the GNU General Public
* License for more details.
*
* The GNU General Public License should be included with
* this file. If not, you can view it at
* http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
* or write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 ,
* USA
*
*********************************************************************/
#include "project.h"
#ifdef __cplusplus
extern "C" {
#endif
... function headers here ...
/* Revision control strings from this header and associated .c file */
extern const char FILENAME_rcs[];
extern const char FILENAME_h_rcs[];
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* ndef _FILENAME_H */
/*
Local Variables:
tab-width: 3
end:
*/
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Example for function
comments:</i></span></p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
/*********************************************************************
*
* Function : FUNCTION_NAME
*
* Description : (Fill me in with a good description!)
*
* parameters :
* 1 : param1 = pointer to an important thing
* 2 : x = pointer to something else
*
* Returns : 0 => Ok, everything else is an error.
*
*********************************************************************/
int FUNCTION_NAME(void *param1, const char *x)
{
...
return 0;
}
</pre>
</td>
</tr>
</table>
<p><span class="emphasis"><i class="EMPHASIS">Note:</i></span> If we
all follow this practice, we should be able to parse our code to create
a "self-documenting" web page.</p>
</div>
</div>
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