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<html>
<head>
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<title>Overview</title>
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</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="bbv2.overview"></a>Overview</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="overview.html#bbv2.overview.concepts">Concepts</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.jam_language">Boost.Jam Language</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.configuration">Configuration</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.invocation">Invocation</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.targets">Declaring Targets</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.projects">Projects</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.build_process">The Build Process</a></span></dt>
</dl></div>
<p>
This section will provide the information necessary to create your own
projects using Boost.Build. The information provided here is relatively
high-level, and <a class="xref" href="reference.html" title="Reference">the section called “Reference”</a> as well as the on-line
help system must be used to obtain low-level documentation (see <a class="xref" href="overview.html#bbv2.reference.init.options.help"><code class="option">--help</code></a>).
</p>
<p>
Boost.Build actually consists of two parts - Boost.Jam, a build engine
with its own interpreted language, and Boost.Build itself, implemented in
Boost.Jam's language. The chain of events when you type
<span class="command"><strong>b2</strong></span> on the command line is as follows:
</p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem"><p>
The Boost.Build executable tries to find Boost.Build modules and
loads the top-level module. The exact process is described in <a class="xref" href="reference.html#bbv2.reference.init" title="Initialization">the section called “Initialization”</a>
</p></li>
<li class="listitem"><p>
The top-level module loads user-defined configuration files,
<code class="filename">user-config.jam</code> and
<code class="filename">site-config.jam</code>, which define available toolsets.
</p></li>
<li class="listitem"><p>
The Jamfile in the current directory is read. That in turn might
cause reading of further Jamfiles. As a result, a tree of projects
is created, with targets inside projects.
</p></li>
<li class="listitem"><p>
Finally, using the build request specified on the command line,
Boost.Build decides which targets should be built and how. That
information is passed back to Boost.Jam, which takes care of
actually running the scheduled build action commands.
</p></li>
</ol></div>
<p>
</p>
<p>
So, to be able to successfully use Boost.Build, you need to know only four
things:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
<a class="link" href="overview.html#bbv2.overview.configuration" title="Configuration">How to configure
Boost.Build</a>
</p></li>
<li class="listitem"><p>
<a class="link" href="overview.html#bbv2.overview.targets" title="Declaring Targets">How to declare targets in
Jamfiles</a>
</p></li>
<li class="listitem"><p>
<a class="link" href="overview.html#bbv2.overview.build_process" title="The Build Process">How the build process
works</a>
</p></li>
<li class="listitem"><p>
Some Basics about the Boost.Jam language. See <a class="xref" href="overview.html#bbv2.overview.jam_language" title="Boost.Jam Language">the section called “Boost.Jam Language”</a>.
</p></li>
</ul></div>
<p>
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.concepts"></a>Concepts</h3></div></div></div>
<p>Boost.Build has a few unique concepts that are introduced in this section. The best
way to explain the concepts is by comparison with more classical build tools.</p>
<p>
When using any flavour of make, you directly specify <em class="firstterm">targets</em>
and commands that are used to create them from other target. The below example
creates <code class="filename">a.o</code> from <code class="filename">a.c</code> using a hardcoded
compiler invocation command.
</p>
<pre class="programlisting">
a.o: a.c
g++ -o a.o -g a.c
</pre>
<p>
This is a rather low-level description mechanism and it's hard to adjust commands, options,
and sets of created targets depending on the compiler and operating system used.
</p>
<p>
To improve portability, most modern build system provide a set of higher-level
functions that can be used in build description files. Consider this example:
</p>
<pre class="programlisting">
add_program ("a", "a.c")
</pre>
<p>
This is a function call that creates the targets necessary to create a executable file
from the source file <code class="filename">a.c</code>. Depending on configured properties,
different command lines may be used. However, <code class="computeroutput">add_program</code> is higher-level,
but rather thin level. All targets are created immediately when the build description
is parsed, which makes it impossible to perform multi-variant builds. Often, change
in any build property requires a complete reconfiguration of the build tree.
</p>
<p>
In order to support true multivariant builds, Boost.Build introduces the concept of a
<a class="indexterm" name="idp261856456"></a>
<a class="indexterm" name="idp261857128"></a>
<em class="firstterm">metatarget</em>—an object that is created when the build description
is parsed and can be called later with specific build properties to generate
actual targets.
</p>
<p>
Consider an example:
</p>
<pre class="programlisting">
exe a : a.cpp ;
</pre>
<p>
When this declaration is parsed, Boost.Build creates a metatarget, but does not
yet decide what files must be created, or what commands must be used. After
all build files are parsed, Boost.Build considers the properties requested on the
command line. Supposed you have invoked Boost.Build with:
</p>
<pre class="screen">
b2 toolset=gcc toolset=msvc
</pre>
<p>
In that case, the metatarget will be called twice, once with <code class="computeroutput">toolset=gcc</code>
and once with <code class="computeroutput">toolset=msvc</code>. Both invocations will produce concrete
targets, that will have different extensions and use different command lines.
</p>
<p>
Another key concept is
<a class="indexterm" name="idp261860680"></a>
<em class="firstterm">build property</em>. A build property is a variable
that affects the build process. It can be specified on the command line, and is
passed when calling a metatarget. While all build tools have a similar mechanism,
Boost.Build differs by requiring that all build properties are declared in advance,
and providing a large set of properties with portable semantics.
</p>
<p>
The final concept is <a class="indexterm" name="idp261861656"></a>
<em class="firstterm">property propagation</em>. Boost.Build does not require that every
metatarget is called with the same properties. Instead, the
"top-level" metatargets are called with the properties specified on the command line.
Each metatarget can elect to augment or override some properties (in particular,
using the requirements mechanism, see <a class="xref" href="overview.html#bbv2.overview.targets.requirements" title="Requirements">the section called “Requirements”</a>).
Then, the dependency metatargets are called with the modified properties and produce
concrete targets that are then used in the build process. Of course, dependency metatargets
maybe in turn modify build properties and have dependencies of their own.
</p>
<p>For a more in-depth treatment of the requirements and concepts, you may refer
to <a href="http://syrcose.ispras.ru/2009/files/04_paper.pdf" target="_top">SYRCoSE 2009 Boost.Build article</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.jam_language"></a>Boost.Jam Language</h3></div></div></div>
<p>
This section will describe the basics of the Boost.Jam language—just
enough for writing Jamfiles. For more information, please see the
<a class="link" href="../">Boost.Jam</a> documentation.
</p>
<p>
<a class="link" href="../">Boost.Jam</a> has an interpreted, procedural
language. On the lowest level, a <a class="link" href="../">Boost.Jam
</a> program consists of variables and <a class="indexterm" name="idp261867064"></a> <em class="firstterm">rules</em> (the Jam term for
functions). They are grouped into modules—there is one global
module and a number of named modules. Besides that, a <a class="link" href="../">Boost.Jam</a> program contains classes and class
instances.
</p>
<p>
Syntantically, a <a class="link" href="../">Boost.Jam</a> program
consists of two kind of elements—keywords (which have a special
meaning to <a class="link" href="../">Boost.Jam</a>) and literals.
Consider this code:
</p>
<pre class="programlisting">
a = b ;
</pre>
<p>
which assigns the value <code class="literal">b</code> to the variable <code class="literal">a
</code>. Here, <code class="literal">=</code> and <code class="literal">;</code> are
keywords, while <code class="literal">a</code> and <code class="literal">b</code> are
literals.
</p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
All syntax elements, even keywords, must be separated by spaces. For
example, omitting the space character before <code class="literal">;</code>
will lead to a syntax error.
</p></td></tr>
</table></div>
<p>
If you want to use a literal value that is the same as some keyword, the
value can be quoted:
</p>
<pre class="programlisting">
a = "=" ;
</pre>
<p>
</p>
<p>
All variables in <a class="link" href="../">Boost.Jam</a> have the same
type—list of strings. To define a variable one assigns a value to
it, like in the previous example. An undefined variable is the same as a
variable with an empty value. Variables can be accessed using the
<code class="computeroutput">$(<em class="replaceable"><code>variable</code></em>)</code> syntax. For example:
</p>
<pre class="programlisting">
a = $(b) $(c) ;
</pre>
<p>
</p>
<p>
Rules are defined by specifying the rule name, the parameter names, and
the allowed value list size for each parameter.
</p>
<pre class="programlisting">
rule <em class="replaceable"><code>example</code></em>
(
<em class="replaceable"><code>parameter1</code></em> :
<em class="replaceable"><code>parameter2 ?</code></em> :
<em class="replaceable"><code>parameter3 +</code></em> :
<em class="replaceable"><code>parameter4 *</code></em>
)
{
# rule body
}
</pre>
<p>
When this rule is called, the list passed as the first argument must
have exactly one value. The list passed as the second argument can
either have one value of be empty. The two remaining arguments can be
arbitrarily long, but the third argument may not be empty.
</p>
<p>
The overview of <a class="link" href="../">Boost.Jam</a> language
statements is given below:
</p>
<pre class="programlisting">
helper 1 : 2 : 3 ;
x = [ helper 1 : 2 : 3 ] ;
</pre>
<p>
This code calls the named rule with the specified arguments. When the
result of the call must be used inside some expression, you need to add
brackets around the call, like shown on the second line.
</p>
<pre class="programlisting">
if cond { statements } [ else { statements } ]
</pre>
<p>
This is a regular if-statement. The condition is composed of:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
Literals (true if at least one string is not empty)
</p></li>
<li class="listitem"><p>
Comparisons: <code class="computeroutput">a <em class="replaceable"><code>operator</code></em> b</code>
where <em class="replaceable"><code>operator</code></em> is one of
<code class="computeroutput">=</code>, <code class="computeroutput">!=</code>, <code class="computeroutput"><</code>,
<code class="computeroutput">></code>, <code class="computeroutput"><=</code> or <code class="computeroutput">>=</code>. The
comparison is done pairwise between each string in the left and
the right arguments.
</p></li>
<li class="listitem"><p>
Logical operations: <code class="computeroutput">! a</code>, <code class="computeroutput">a && b</code>,
<code class="computeroutput">a || b</code>
</p></li>
<li class="listitem"><p>
Grouping: <code class="computeroutput">( cond )</code>
</p></li>
</ul></div>
<p>
</p>
<pre class="programlisting">
for var in list { statements }
</pre>
<p>
Executes statements for each element in list, setting the variable
<code class="varname">var</code> to the element value.
</p>
<pre class="programlisting">
while cond { statements }
</pre>
<p>
Repeatedly execute statements while cond remains true upon entry.
</p>
<pre class="programlisting">
return values ;
</pre>
<p>
This statement should be used only inside a rule and assigns
<code class="computeroutput">values</code> to the return value of the rule.
</p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top">
<p>
The <code class="computeroutput">return</code> statement does not exit the rule. For
example:
</p>
<pre class="programlisting">
rule test ( )
{
if 1 = 1
{
return "reasonable" ;
}
return "strange" ;
}
</pre>
<p>
will return <code class="literal">strange</code>, not
<code class="literal">reasonable</code>.
</p>
</td></tr>
</table></div>
<p>
</p>
<pre class="programlisting">
import <em class="replaceable"><code>module</code></em> ;
import <em class="replaceable"><code>module</code></em> : <em class="replaceable"><code>rule</code></em> ;
</pre>
<p>
The first form imports the specified module. All rules from that
module are made available using the qualified name: <code class="computeroutput"><em class="replaceable"><code>
module</code></em>.<em class="replaceable"><code>rule</code></em></code>. The second
form imports the specified rules only, and they can be called using
unqualified names.
</p>
<p><a name="bbv2.overview.jam_language.actions"></a>
Sometimes, you need to specify the actual command lines to be used
when creating targets. In the jam language, you use named actions to do
this. For example:
</p>
<pre class="programlisting">
actions create-file-from-another
{
create-file-from-another $(<) $(>)
}
</pre>
<p>
This specifies a named action called <code class="literal">
create-file-from-another</code>. The text inside braces is the
command to invoke. The <code class="literal">$(<)</code> variable will be
expanded to a list of generated files, and the <code class="literal">$(>)
</code> variable will be expanded to a list of source files.
</p>
<p>
To adjust the command line flexibly, you can define a rule with the same
name as the action and taking three parameters—targets, sources and
properties. For example:
</p>
<pre class="programlisting">
rule create-file-from-another ( targets * : sources * : properties * )
{
if <variant>debug in $(properties)
{
OPTIONS on $(targets) = --debug ;
}
}
actions create-file-from-another
{
create-file-from-another $(OPTIONS) $(<) $(>)
}
</pre>
<p>
In this example, the rule checks if a certain build property is specified.
If so, it sets the variable <code class="varname">OPTIONS</code> that is then used
inside the action. Note that the variables set "on a target" will be
visible only inside actions building that target, not globally. Were
they set globally, using variable named <code class="varname">OPTIONS</code> in
two unrelated actions would be impossible.
</p>
<p>
More details can be found in the Jam reference, <a class="xref" href="../jam/language.html#jam.language.rules" title="Rules">the section called “Rules”</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.configuration"></a>Configuration</h3></div></div></div>
<p>
On startup, Boost.Build searches and reads two configuration files:
<code class="filename">site-config.jam</code> and <code class="filename">user-config.jam</code>.
The first one is usually installed and maintained by a system administrator, and
the second is for the user to modify. You can edit the one in the top-level
directory of your Boost.Build installation or create a copy in your home
directory and edit the copy. The following table explains where both files
are searched.
</p>
<div class="table">
<a name="bbv2.reference.init.config"></a><p class="title"><b>Table 43.1. Search paths for configuration files</b></p>
<div class="table-contents"><table class="table" summary="Search paths for configuration files">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th> </th>
<th>site-config.jam</th>
<th>user-config.jam</th>
</tr></thead>
<tbody>
<tr>
<td>Linux</td>
<td>
<p><code class="computeroutput">/etc</code></p>
<p><code class="computeroutput">$HOME</code></p>
<p><code class="computeroutput">$BOOST_BUILD_PATH</code></p>
</td>
<td>
<p><code class="computeroutput">$HOME</code></p>
<p><code class="computeroutput">$BOOST_BUILD_PATH</code></p>
</td>
</tr>
<tr>
<td>Windows</td>
<td>
<p><code class="computeroutput">%SystemRoot%</code></p>
<p><code class="computeroutput">%HOMEDRIVE%%HOMEPATH%</code></p>
<p><code class="computeroutput">%HOME%</code></p>
<p><code class="computeroutput">%BOOST_BUILD_PATH%</code></p>
</td>
<td>
<p><code class="computeroutput">%HOMEDRIVE%%HOMEPATH%</code></p>
<p><code class="computeroutput">%HOME%</code></p>
<p><code class="computeroutput">%BOOST_BUILD_PATH%</code></p>
</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>
You can use the <span class="command"><strong>--debug-configuration</strong></span> option to
find which configuration files are actually loaded.
</p></td></tr>
</table></div>
<p>
Usually, <code class="filename">user-config.jam</code> just defines the available compilers
and other tools (see <a class="xref" href="faq.html#bbv2.recipies.site-config" title="Targets in site-config.jam">the section called “Targets in site-config.jam”</a> for more advanced
usage). A tool is configured using the following syntax:
</p>
<pre class="programlisting">
using <em class="replaceable"><code>tool-name</code></em> : ... ;
</pre>
<p>
The <code class="computeroutput">using</code> rule is given the name of tool, and
will make that tool available to Boost.Build. For example,
</p>
<pre class="programlisting">
using gcc ;
</pre>
<p> will make the <a href="http://gcc.gnu.org" target="_top">GCC</a> compiler available.
</p>
<p>
All the supported tools are documented in <a class="xref" href="reference.html#bbv2.reference.tools" title="Builtin tools">the section called “Builtin tools”</a>,
including the specific options they take. Some general notes that apply to most
C++ compilers are below.
</p>
<p>
For all the C++ compiler toolsets that Boost.Build supports
out-of-the-box, the list of parameters to
<code class="computeroutput">using</code> is the same: <em class="parameter"><code>toolset-name</code></em>, <em class="parameter"><code>version</code></em>, <em class="parameter"><code>invocation-command</code></em>, and <em class="parameter"><code>options</code></em>.
</p>
<p>If you have a single compiler, and the compiler executable
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>has its “usual name” and is in the
<code class="envar">PATH</code>, or</p></li>
<li class="listitem"><p>was installed in a standard “installation
directory”, or</p></li>
<li class="listitem"><p>can be found using a global system like the Windows
registry.</p></li>
</ul></div>
<p>
it can be configured by simply:</p>
<pre class="programlisting">
using <em class="replaceable"><code>tool-name</code></em> ;
</pre>
<p>If the compiler is installed in a custom directory, you should provide the
command that invokes the compiler, for example:</p>
<pre class="programlisting">
using gcc : : g++-3.2 ;
using msvc : : "Z:/Programs/Microsoft Visual Studio/vc98/bin/cl" ;
</pre>
<p>
Some Boost.Build toolsets will use that path to take additional actions
required before invoking the compiler, such as calling vendor-supplied
scripts to set up its required environment variables. When the compiler
executables for C and C++ are different, the path to the C++ compiler
executable must be specified. The command can
be any command allowed by the operating system. For example:
</p>
<pre class="programlisting">
using msvc : : echo Compiling && foo/bar/baz/cl ;
</pre>
<p>
will work.
</p>
<p>
To configure several versions of a toolset, simply invoke the
<code class="computeroutput">using</code> rule multiple times:
</p>
<pre class="programlisting">
using gcc : 3.3 ;
using gcc : 3.4 : g++-3.4 ;
using gcc : 3.2 : g++-3.2 ;
</pre>
<p>
Note that in the first call to <code class="computeroutput">using</code>, the
compiler found in the <code class="envar">PATH</code> will be used, and there is no
need to explicitly specify the command.
</p>
<p>
Many of toolsets have an <em class="parameter"><code>options</code></em>
parameter to fine-tune the configuration. All of
Boost.Build's standard compiler toolsets accept four options
<code class="varname">cflags</code>, <code class="varname">cxxflags</code>,
<code class="varname">compileflags</code> and <code class="varname">linkflags</code> as <em class="parameter"><code>options</code></em> specifying flags that will be
always passed to the corresponding tools. Values of the
<code class="varname">cflags</code> feature are passed directly to the C
compiler, values of the <code class="varname">cxxflags</code> feature are
passed directly to the C++ compiler, and values of the
<code class="varname">compileflags</code> feature are passed to both. For
example, to configure a <span class="command"><strong>gcc</strong></span> toolset so that it
always generates 64-bit code you could write:
</p>
<pre class="programlisting">
using gcc : 3.4 : : <compileflags>-m64 <linkflags>-m64 ;
</pre>
<p>
</p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
Although the syntax used to specify toolset options is very similar
to syntax used to specify requirements in Jamfiles, the toolset options
are not the same as features. Don't try to specify a feature value
in toolset initialization.
</p></td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.invocation"></a>Invocation</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="overview.html#bbv2.overview.invocation.examples">Examples</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.invocation.options">Options</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.invocation.properties">Properties</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.invocation.targets">Targets</a></span></dt>
</dl></div>
<p>To invoke Boost.Build, type <span class="command"><strong>b2</strong></span> on the command line. Three kinds
of command-line tokens are accepted, in any order:</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">options</span></dt>
<dd><p>Options start with either one or two dashes. The standard options
are listed below, and each project may add additional options</p></dd>
<dt><span class="term">properties</span></dt>
<dd><p>Properties specify details of what you want to build (e.g. debug
or release variant). Syntactically, all command line tokens with an equal sign in them
are considered to specify properties. In the simplest form, a property looks like
<span class="command"><strong><em class="replaceable"><code>feature</code></em>=<em class="replaceable"><code>value</code></em></strong></span>
</p></dd>
<dt><span class="term">target</span></dt>
<dd><p>All tokens that are neither options nor properties specify
what targets to build. The available targets entirely depend on the project
you are building.</p></dd>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.overview.invocation.examples"></a>Examples</h4></div></div></div>
<p>To build all targets defined in the Jamfile in the current directory with the default properties, run:
</p>
<pre class="screen">
b2
</pre>
<p>
</p>
<p>To build specific targets, specify them on the command line:
</p>
<pre class="screen">
b2 lib1 subproject//lib2
</pre>
<p>
</p>
<p>To request a certain value for some property, add <code class="literal">
<em class="replaceable"><code>property</code></em>=<em class="replaceable"><code>value</code></em></code> to the command line:
</p>
<pre class="screen">
b2 toolset=gcc variant=debug optimization=space
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.overview.invocation.options"></a>Options</h4></div></div></div>
<p>Boost.Build recognizes the following command line options.</p>
<div class="variablelist"><dl class="variablelist">
<dt>
<a name="bbv2.reference.init.options.help"></a><span class="term"><code class="option">--help</code></span>
</dt>
<dd><p>Invokes the online help system. This prints general
information on how to use the help system with additional
--help* options.
</p></dd>
<dt><span class="term"><code class="option">--clean</code></span></dt>
<dd><p>Cleans all targets in the current directory and
in any subprojects. Note that unlike the <code class="literal">clean</code>
target in make, you can use <code class="literal">--clean</code>
together with target names to clean specific targets.</p></dd>
<dt><span class="term"><code class="option">--clean-all</code></span></dt>
<dd><p>Cleans all targets,
no matter where they are defined. In particular, it will clean targets
in parent Jamfiles, and targets defined under other project roots.
</p></dd>
<dt><span class="term"><code class="option">--build-dir</code></span></dt>
<dd>
<p>Changes the build directories for all project roots being built. When
this option is specified, all Jamroot files must declare a project name.
The build directory for the project root will be computed by concatanating
the value of the <code class="option">--build-dir</code> option, the project name
specified in Jamroot, and the build dir specified in Jamroot
(or <code class="literal">bin</code>, if none is specified).
</p>
<p>The option is primarily useful when building from read-only
media, when you can't modify Jamroot.
</p>
</dd>
<dt><span class="term"><code class="option">--abbreviate-paths</code></span></dt>
<dd><p>Compresses target paths by abbreviating each component.
This option is useful to keep paths from becoming longer than
the filesystem supports. See also <a class="xref" href="reference.html#bbv2.reference.buildprocess.targetpath" title="Target Paths">the section called “Target Paths”</a>.
</p></dd>
<dt><span class="term"><code class="option">--hash</code></span></dt>
<dd><p>Compresses target paths using an MD5 hash. This option is
useful to keep paths from becoming longer than the filesystem
supports. This option produces shorter paths than --abbreviate-paths
does, but at the cost of making them less understandable.
See also <a class="xref" href="reference.html#bbv2.reference.buildprocess.targetpath" title="Target Paths">the section called “Target Paths”</a>.
</p></dd>
<dt><span class="term"><code class="option">--version</code></span></dt>
<dd><p>Prints information on the Boost.Build and Boost.Jam
versions.
</p></dd>
<dt><span class="term"><code class="option">-a</code></span></dt>
<dd><p>Causes all files to be rebuilt.</p></dd>
<dt><span class="term"><code class="option">-n</code></span></dt>
<dd><p>Do no execute the commands, only print them.</p></dd>
<dt><span class="term"><code class="option">-q</code></span></dt>
<dd><p>Stop at the first error, as opposed to continuing to build targets
that don't depend on the failed ones.</p></dd>
<dt><span class="term"><code class="option">-j <em class="replaceable"><code>N</code></em></code></span></dt>
<dd><p>Run up to <em class="replaceable"><code>N</code></em> commands in parallel.</p></dd>
<dt><span class="term"><code class="option">--debug-configuration</code></span></dt>
<dd><p>Produces debug information about the loading of Boost.Build
and toolset files.</p></dd>
<dt><span class="term"><code class="option">--debug-building</code></span></dt>
<dd><p>Prints what targets are being built and with what properties.
</p></dd>
<dt><span class="term"><code class="option">--debug-generators</code></span></dt>
<dd><p>Produces debug output from the generator search process.
Useful for debugging custom generators.
</p></dd>
<dt><span class="term"><code class="option">-d0</code></span></dt>
<dd><p>Supress all informational messages.</p></dd>
<dt><span class="term"><code class="option">-d <em class="replaceable"><code>N</code></em></code></span></dt>
<dd>
<p>Enable cummulative debugging levels from 1 to n. Values are:
</p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">Show the actions taken for building targets, as they are executed (the default).</li>
<li class="listitem">Show "quiet" actions and display all action text, as they are executed.</li>
<li class="listitem">Show dependency analysis, and target/source timestamps/paths.</li>
<li class="listitem">Show arguments and timming of shell invocations.</li>
<li class="listitem">Show rule invocations and variable expansions.</li>
<li class="listitem">Show directory/header file/archive scans, and attempts at binding to targets.</li>
<li class="listitem">Show variable settings.</li>
<li class="listitem">Show variable fetches, variable expansions, and evaluation of '"if"' expressions.</li>
<li class="listitem">Show variable manipulation, scanner tokens, and memory usage.</li>
<li class="listitem">Show profile information for rules, both timing and memory.</li>
<li class="listitem">Show parsing progress of Jamfiles.</li>
<li class="listitem">Show graph of target dependencies.</li>
<li class="listitem">Show change target status (fate).</li>
</ol></div>
<p>
</p>
</dd>
<dt><span class="term"><code class="option">-d +<em class="replaceable"><code>N</code></em></code></span></dt>
<dd><p>Enable debugging level <em class="replaceable"><code>N</code></em>.</p></dd>
<dt><span class="term"><code class="option">-o <em class="replaceable"><code>file</code></em></code></span></dt>
<dd><p>Write the updating actions to the specified file instead of running them.
</p></dd>
<dt><span class="term"><code class="option">-s <em class="replaceable"><code>var</code></em>=<em class="replaceable"><code>value</code></em></code></span></dt>
<dd><p>Set the variable <em class="replaceable"><code>var</code></em> to
<em class="replaceable"><code>value</code></em> in the global scope of the jam
language interpreter, overriding variables imported from the
environment.
</p></dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.overview.invocation.properties"></a>Properties</h4></div></div></div>
<p>In the simplest case, the build is performed with a single set of properties,
that you specify on the command line with elements in the form
<span class="command"><strong><em class="replaceable"><code>feature</code></em>=<em class="replaceable"><code>value</code></em></strong></span>.
The complete list of features can be found in <a class="xref" href="reference.html#bbv2.overview.builtins.features" title="Builtin features">the section called “Builtin features”</a>.
The most common features are summarized below.</p>
<div class="table">
<a name="idp261962808"></a><p class="title"><b>Table 43.2. </b></p>
<div class="table-contents"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Feature</th>
<th>Allowed values</th>
<th>Notes</th>
</tr></thead>
<tbody>
<tr>
<td>variant</td>
<td>debug,release</td>
<td> </td>
</tr>
<tr>
<td>link</td>
<td>shared,static</td>
<td>Determines if Boost.Build creates shared or static libraries</td>
</tr>
<tr>
<td>threading</td>
<td>single,multi</td>
<td>Cause the produced binaries to be thread-safe. This requires proper support in the source code itself.</td>
</tr>
<tr>
<td>address-model</td>
<td>32,64</td>
<td>Explicitly request either 32-bit or 64-bit code generation. This typically
requires that your compiler is appropriately configured. Please refer to
<a class="xref" href="reference.html#bbv2.reference.tools.compilers" title="C++ Compilers">the section called “C++ Compilers”</a> and your compiler documentation
in case of problems.</td>
</tr>
<tr>
<td>toolset</td>
<td>(Depends on configuration)</td>
<td>The C++ compiler to use. See <a class="xref" href="reference.html#bbv2.reference.tools.compilers" title="C++ Compilers">the section called “C++ Compilers”</a> for a detailed list.</td>
</tr>
<tr>
<td>include</td>
<td>(Arbitrary string)</td>
<td>Additional include paths for C and C++ compilers.</td>
</tr>
<tr>
<td>define</td>
<td>(Arbitrary string)</td>
<td>Additional macro definitions for C and C++ compilers. The string should be either
<code class="computeroutput">SYMBOL</code> or <code class="computeroutput">SYMBOL=VALUE</code>
</td>
</tr>
<tr>
<td>cxxflags</td>
<td>(Arbitrary string)</td>
<td>Custom options to pass to the C++ compiler.</td>
</tr>
<tr>
<td>cflags</td>
<td>(Arbitrary string)</td>
<td>Custom options to pass to the C compiler.</td>
</tr>
<tr>
<td>linkflags</td>
<td>(Arbitrary string)</td>
<td>Custom options to pass to the C++ linker.</td>
</tr>
<tr>
<td>runtime-link</td>
<td>shared,static</td>
<td>Determines if shared or static version of C and C++ runtimes should be used.</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p>If you have more than one version of a given C++ toolset (e.g. configured in
<code class="filename">user-config.jam</code>, or autodetected, as happens with msvc), you can
request the specific version by passing
<code class="computeroutput"><em class="replaceable"><code>toolset</code></em>-<em class="replaceable"><code>version</code></em></code> as
the value of the <code class="computeroutput">toolset</code> feature, for example <code class="computeroutput">toolset=msvc-8.0</code>.
</p>
<p>
If a feature has a fixed set of values it can be specified more than
once on the command line.
In which case, everything will be built several times --
once for each specified value of a feature. For example, if you use
</p>
<pre class="screen">
b2 link=static link=shared threading=single threading=multi
</pre>
<p>
Then a total of 4 builds will be performed. For convenience,
instead of specifying all requested values of a feature in separate command line elements,
you can separate the values with commas, for example:
</p>
<pre class="screen">
b2 link=static,shared threading=single,multi
</pre>
<p>
The comma has this special meaning only if the feature has a fixed set of values, so
</p>
<pre class="screen">
b2 include=static,shared
</pre>
<p>is not treated specially.</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.overview.invocation.targets"></a>Targets</h4></div></div></div>
<p>All command line elements that are neither options nor properties are the names of the
targets to build. See <a class="xref" href="reference.html#bbv2.reference.ids" title="Target identifiers and references">the section called “Target identifiers and references”</a>. If no target is specified,
the project in the current directory is built.</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.targets"></a>Declaring Targets</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="overview.html#idp261987624">Name</a></span></dt>
<dt><span class="section"><a href="overview.html#idp261997000">Sources</a></span></dt>
<dt><span class="section"><a href="overview.html#bbv2.overview.targets.requirements">Requirements</a></span></dt>
<dt><span class="section"><a href="overview.html#idp262016040">Default Build</a></span></dt>
<dt><span class="section"><a href="overview.html#idp262017704">Additional Information</a></span></dt>
</dl></div>
<p><a name="bbv2.overview.targets.main"></a>
A <em class="firstterm">Main target</em> is a user-defined named
entity that can be built, for example an executable file.
Declaring a main target is usually done using one of the main
target rules described in <a class="xref" href="reference.html#bbv2.reference.rules" title="Builtin rules">the section called “Builtin rules”</a>. The user can also declare
custom main target rules as shown in <a class="xref" href="extender.html#bbv2.extending.rules" title="Main target rules">the section called “Main target rules”</a>.
</p>
<a class="indexterm" name="idp261984472"></a><p>Most main target rules in Boost.Build have the same common
signature:</p>
<a class="indexterm" name="idp261985304"></a><a name="bbv2.main-target-rule-syntax"></a><pre class="programlisting">
rule <em class="replaceable"><code>rule-name</code></em> (
main-target-name :
sources + :
requirements * :
default-build * :
usage-requirements * )
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<em class="parameter"><code>main-target-name</code></em> is the name used
to request the target on command line and to use it from
other main targets. A main target name may contain
alphanumeric characters, dashes
(‘<code class="computeroutput">-</code>’), and underscores
(‘<code class="computeroutput">_</code>’).
</li>
<li class="listitem">
<em class="parameter"><code>sources</code></em> is the list of source files and other main
targets that must be combined.
</li>
<li class="listitem">
<em class="parameter"><code>requirements</code></em> is the list of properties that must always
be present when this main target is built.
</li>
<li class="listitem">
<em class="parameter"><code>default-build</code></em> is the list of properties that will be used
unless some other value of the same feature is already
specified, e.g. on the command line or by propagation from a dependent target.
</li>
<li class="listitem">
<em class="parameter"><code>usage-requirements</code></em> is the list of properties that will be
propagated to all main targets that use this one, i.e. to all its
dependents.
</li>
</ul></div>
<p>
Some main target rules have a different list of parameters as explicitly
stated in their documentation.
</p>
<p>The actual requirements for a target are obtained by refining
the requirements of the project where the target is declared with the
explicitly specified requirements. The same is true for
usage-requirements. More details can be found in
<a class="xref" href="reference.html#bbv2.reference.variants.proprefine" title="Property refinement">the section called “Property refinement”</a>
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="idp261987624"></a>Name</h4></div></div></div>
<p>The name of main target has two purposes. First, it's used to refer to this target from
other targets and from command line. Second, it's used to compute the names of the generated files.
Typically, filenames are obtained from main target name by appending system-dependent suffixes and
prefixes.
</p>
<p>The name of a main target can contain alphanumeric characters,
dashes, undescores and dots. The entire
name is significant when resolving references from other targets. For determining filenames, only the
part before the first dot is taken. For example:</p>
<pre class="programlisting">
obj test.release : test.cpp : <variant>release ;
obj test.debug : test.cpp : <variant>debug ;
</pre>
<p>will generate two files named <code class="filename">test.obj</code> (in two different directories), not
two files named <code class="filename">test.release.obj</code> and <code class="filename">test.debug.obj</code>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="idp261997000"></a>Sources</h4></div></div></div>
<p>The list of sources specifies what should be processed to
get the resulting targets. Most of the time, it's just a list of
files. Sometimes, you'll want to automatically construct the
list of source files rather than having to spell it out
manually, in which case you can use the
<a class="link" href="reference.html#bbv2.reference.rules.glob">glob</a> rule.
Here are two examples:</p>
<pre class="programlisting">
exe a : a.cpp ; # a.cpp is the only source file
exe b : [ glob *.cpp ] ; # all .cpp files in this directory are sources
</pre>
<p>
Unless you specify a file with an absolute path, the name is
considered relative to the source directory — which is typically
the directory where the Jamfile is located, but can be changed as
described in <a class="xref" href="overview.html#bbv2.overview.projects.attributes.projectrule">the section called “Projects”</a>.
</p>
<p>
The list of sources can also refer to other main targets. Targets in
the same project can be referred to by name, while targets in other
projects must be qualified with a directory or a symbolic project
name. The directory/project name is separated from the target name by
a double forward slash. There is no special syntax to distinguish the
directory name from the project name—the part before the double
slash is first looked up as project name, and then as directory name.
For example:
</p>
<pre class="programlisting">
lib helper : helper.cpp ;
exe a : a.cpp helper ;
# Since all project ids start with slash, ".." is a directory name.
exe b : b.cpp ..//utils ;
exe c : c.cpp /boost/program_options//program_options ;
</pre>
<p>
The first exe uses the library defined in the same project. The second
one uses some target (most likely a library) defined by a Jamfile one
level higher. Finally, the third target uses a <a href="http://boost.org" target="_top">C++ Boost</a> library, referring to it using
its absolute symbolic name. More information about target references
can be found in <a class="xref" href="tutorial.html#bbv2.tutorial.libs" title="Dependent Targets">the section called “Dependent Targets”</a> and <a class="xref" href="reference.html#bbv2.reference.ids" title="Target identifiers and references">the section called “Target identifiers and references”</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.overview.targets.requirements"></a>Requirements</h4></div></div></div>
<a class="indexterm" name="idp262003064"></a><p>Requirements are the properties that should always be present when
building a target. Typically, they are includes and defines:
</p>
<pre class="programlisting">
exe hello : hello.cpp : <include>/opt/boost <define>MY_DEBUG ;
</pre>
<p>
There are a number of other features, listed in
<a class="xref" href="reference.html#bbv2.overview.builtins.features" title="Builtin features">the section called “Builtin features”</a>. For example if
a library can only be built statically, or a file can't be compiled
with optimization due to a compiler bug, one can use
</p>
<pre class="programlisting">
lib util : util.cpp : <link>static ;
obj main : main.cpp : <optimization>off ;
</pre>
<p>
</p>
<p><a name="bbv2.overview.targets.requirements.conditional"></a>Sometimes, particular relationships need to be maintained
among a target's build properties. This can be achieved with
<em class="firstterm">conditional
requirements</em>. For example, you might want to set
specific <code class="computeroutput">#defines</code> when a library is built as shared,
or when a target's <code class="computeroutput">release</code> variant is built in
release mode.
</p>
<pre class="programlisting">
lib network : network.cpp
: <span class="bold"><strong><link>shared:<define>NEWORK_LIB_SHARED</strong></span>
<variant>release:<define>EXTRA_FAST
;
</pre>
<p>
In the example above, whenever <code class="filename">network</code> is
built with <code class="computeroutput"><link>shared</code>,
<code class="computeroutput"><define>NEWORK_LIB_SHARED</code> will be in its
properties, too.
</p>
<p>You can use several properties in the condition, for example:
</p>
<pre class="programlisting">
lib network : network.cpp
: <toolset>gcc,<optimization>speed:<define>USE_INLINE_ASSEMBLER
;
</pre>
<p>
</p>
<p><a name="bbv2.overview.targets.requirements.indirect"></a>
A more powerful variant of conditional requirements
is <em class="firstterm">indirect conditional requirements</em>.
You can provide a rule that will be called with the current build properties and can compute additional properties
to be added. For example:
</p>
<pre class="programlisting">
lib network : network.cpp
: <conditional>@my-rule
;
rule my-rule ( properties * )
{
local result ;
if <toolset>gcc <optimization>speed in $(properties)
{
result += <define>USE_INLINE_ASSEMBLER ;
}
return $(result) ;
}
</pre>
<p>
This example is equivalent to the previous one, but for complex cases, indirect conditional
requirements can be easier to write and understand.
</p>
<p>Requirements explicitly specified for a target are usually
combined with the requirements specified for the containing project. You
can cause a target to completely ignore a specific project requirement
using the syntax by adding a minus sign before the property, for example:
</p>
<pre class="programlisting">
exe main : main.cpp : <span class="bold"><strong>-<define>UNNECESSARY_DEFINE</strong></span> ;
</pre>
<p>
This syntax is the only way to ignore free properties, such as defines,
from a parent. It can be also useful for ordinary properties. Consider
this example:
</p>
<pre class="programlisting">
project test : requirements <threading>multi ;
exe test1 : test1.cpp ;
exe test2 : test2.cpp : <threading>single ;
exe test3 : test3.cpp : -<threading>multi ;
</pre>
<p>
Here, <code class="computeroutput">test1</code> inherits the project requirements and will always
be built in multi-threaded mode. The <code class="computeroutput">test2</code> target
<span class="emphasis"><em>overrides</em></span> the project's requirements and will
always be built in single-threaded mode. In contrast, the
<code class="computeroutput">test3</code> target <span class="emphasis"><em>removes</em></span> a property
from the project requirements and will be built either in single-threaded or
multi-threaded mode depending on which variant is requested by the
user.</p>
<p>Note that the removal of requirements is completely textual:
you need to specify exactly the same property to remove it.</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="idp262016040"></a>Default Build</h4></div></div></div>
<p>The <code class="varname">default-build</code> parameter
is a set of properties to be used if the build request does
not otherwise specify a value for features in the set. For example:
</p>
<pre class="programlisting">
exe hello : hello.cpp : : <threading>multi ;
</pre>
<p>
would build a multi-threaded target unless the user
explicitly requests a single-threaded version. The difference between
the requirements and the default-build is that the requirements cannot be
overridden in any way.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="idp262017704"></a>Additional Information</h4></div></div></div>
<p>
The ways a target is built can be so different that
describing them using conditional requirements would be
hard. For example, imagine that a library actually uses
different source files depending on the toolset used to build
it. We can express this situation using <em class="firstterm">target
alternatives</em>:
</p>
<pre class="programlisting">
lib demangler : dummy_demangler.cpp ; # alternative 1
lib demangler : demangler_gcc.cpp : <toolset>gcc ; # alternative 2
lib demangler : demangler_msvc.cpp : <toolset>msvc ; # alternative 3
</pre>
<p>
In the example above, when built with <code class="literal">gcc</code>
or <code class="literal">msvc</code>, <code class="filename">demangler</code>
will use a source file specific to the toolset. Otherwise, it
will use a generic source file,
<code class="filename">dummy_demangler.cpp</code>.
</p>
<p>It is possible to declare a target inline, i.e. the "sources"
parameter may include calls to other main rules. For example:</p>
<pre class="programlisting">
exe hello : hello.cpp
[ obj helpers : helpers.cpp : <optimization>off ] ;</pre>
<p>
Will cause "helpers.cpp" to be always compiled without
optimization. When referring to an inline main target, its declared
name must be prefixed by its parent target's name and two dots. In
the example above, to build only helpers, one should run
<code class="computeroutput">b2 hello..helpers</code>.
</p>
<p>When no target is requested on the command line, all targets in the
current project will be built. If a target should be built only by
explicit request, this can be expressed by the
<a class="link" href="reference.html#bbv2.reference.rules.explicit">explicit</a> rule:
</p>
<pre class="programlisting">
explicit install_programs ;</pre>
<p>
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.projects"></a>Projects</h3></div></div></div>
<p>As mentioned before, targets are grouped into projects,
and each Jamfile is a separate project. Projects are useful
because they allow us to group related targets together, define
properties common to all those targets, and assign a symbolic
name to the project that can be used in referring to its
targets.
</p>
<p>Projects are named using the
<code class="computeroutput">project</code> rule, which has the
following syntax:
</p>
<pre class="programlisting">
project <em class="replaceable"><code>id</code></em> : <em class="replaceable"><code>attributes</code></em> ;
</pre>
<p>
Here, <em class="replaceable"><code>attributes</code></em> is a sequence of
rule arguments, each of which begins with an attribute-name
and is followed by any number of build properties. The list
of attribute names along with its handling is also shown in
the table below. For example, it is possible to write:
</p>
<pre class="programlisting">
project tennis
: requirements <threading>multi
: default-build release
;
</pre>
<p>
</p>
<p>The possible attributes are listed below.</p>
<p><span class="emphasis"><em>Project id</em></span> is a short way to denote a project, as
opposed to the Jamfile's pathname. It is a hierarchical path,
unrelated to filesystem, such as "boost/thread". <a class="link" href="reference.html#bbv2.reference.ids" title="Target identifiers and references">Target references</a> make use of project ids to
specify a target.</p>
<p><span class="emphasis"><em>Source location</em></span> specifies the directory where sources
for the project are located.</p>
<p><span class="emphasis"><em>Project requirements</em></span> are requirements that apply to
all the targets in the projects as well as all subprojects.</p>
<p><span class="emphasis"><em>Default build</em></span> is the build request that should be
used when no build request is specified explicitly.</p>
<p><a name="bbv2.overview.projects.attributes.projectrule"></a>
The default values for those attributes are
given in the table below.
</p>
<div class="table">
<a name="idp262030712"></a><p class="title"><b>Table 43.3. </b></p>
<div class="table-contents"><table class="table" summary="">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Attribute</th>
<th>Name</th>
<th>Default value</th>
<th>Handling by the <code class="computeroutput">project</code>
rule</th>
</tr></thead>
<tbody>
<tr>
<td>Project id</td>
<td>none</td>
<td>none</td>
<td>Assigned from the first parameter of the 'project' rule.
It is assumed to denote absolute project id.</td>
</tr>
<tr>
<td>Source location</td>
<td><code class="literal">source-location</code></td>
<td>The location of jamfile for the project</td>
<td>Sets to the passed value</td>
</tr>
<tr>
<td>Requirements</td>
<td><code class="literal">requirements</code></td>
<td>The parent's requirements</td>
<td>The parent's requirements are refined with the passed
requirement and the result is used as the project
requirements.</td>
</tr>
<tr>
<td>Default build</td>
<td><code class="literal">default-build</code></td>
<td>none</td>
<td>Sets to the passed value</td>
</tr>
<tr>
<td>Build directory</td>
<td><code class="literal">build-dir</code></td>
<td>Empty if the parent has no build directory set.
Otherwise, the parent's build directory with the
relative path from parent to the current project
appended to it.
</td>
<td>Sets to the passed value, interpreted as relative to the
project's location.</td>
</tr>
</tbody>
</table></div>
</div>
<p><br class="table-break">
</p>
<p>Besides defining projects and main targets, Jamfiles
often invoke various utility rules. For the full list of rules
that can be directly used in Jamfile see
<a class="xref" href="reference.html#bbv2.reference.rules" title="Builtin rules">the section called “Builtin rules”</a>.
</p>
<p>Each subproject inherits attributes, constants and rules
from its parent project, which is defined by the nearest
Jamfile in an ancestor directory above
the subproject. The top-level project is declared in a file
called <code class="filename">Jamroot</code> rather than
<code class="filename">Jamfile</code>. When loading a project,
Boost.Build looks for either <code class="filename">Jamroot</code> or
<code class="computeroutput">Jamfile</code>. They are handled identically, except
that if the file is called <code class="filename">Jamroot</code>, the
search for a parent project is not performed.
</p>
<p>Even when building in a subproject directory, parent
project files are always loaded before those of their
subprojects, so that every definition made in a parent project
is always available to its children. The loading order of any
other projects is unspecified. Even if one project refers to
another via the <code class="computeroutput">use-project</code> or a target reference,
no specific order should be assumed.
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>Giving the root project the special name
“<code class="filename">Jamroot</code>” ensures that
Boost.Build won't misinterpret a directory above it as the
project root just because the directory contains a Jamfile.
</p></td></tr>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="bbv2.overview.build_process"></a>The Build Process</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="overview.html#bbv2.overview.build_request">Build Request</a></span></dt>
<dt><span class="section"><a href="overview.html#idp262049704">Building a main target</a></span></dt>
<dt><span class="section"><a href="overview.html#idp262056648">Building a Project</a></span></dt>
</dl></div>
<p>When you've described your targets, you want Boost.Build to run the
right tools and create the needed targets.
This section will describe
two things: how you specify what to build, and how the main targets are
actually constructed.
</p>
<p>The most important thing to note is that in Boost.Build, unlike
other build tools, the targets you declare do not correspond to specific
files. What you declare in a Jamfile is more like a “metatarget.”
Depending on the properties you specify on the command line,
each metatarget will produce a set of real targets corresponding
to the requested properties. It is quite possible that the same
metatarget is built several times with different properties,
producing different files.
</p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>
This means that for Boost.Build, you cannot directly obtain a build
variant from a Jamfile. There could be several variants requested by the
user, and each target can be built with different properties.
</p></td></tr>
</table></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bbv2.overview.build_request"></a>Build Request</h4></div></div></div>
<p>
The command line specifies which targets to build and with which
properties. For example:
</p>
<pre class="programlisting">
b2 app1 lib1//lib1 toolset=gcc variant=debug optimization=full
</pre>
<p>
would build two targets, "app1" and "lib1//lib1" with the specified
properties. You can refer to any targets, using
<a class="link" href="reference.html#bbv2.reference.ids" title="Target identifiers and references">target id</a> and specify arbitrary
properties. Some of the properties are very common, and for them the name
of the property can be omitted. For example, the above can be written as:
</p>
<pre class="programlisting">
b2 app1 lib1//lib1 gcc debug optimization=full
</pre>
<p>
The complete syntax, which has some additional shortcuts, is
described in <a class="xref" href="overview.html#bbv2.overview.invocation" title="Invocation">the section called “Invocation”</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="idp262049704"></a>Building a main target</h4></div></div></div>
<p>When you request, directly or indirectly, a build of a main target
with specific requirements, the following steps are done. Some brief
explanation is provided, and more details are given in <a class="xref" href="reference.html#bbv2.reference.buildprocess" title="Build process">the section called “Build process”</a>.
</p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem"><p>Applying default build. If the default-build
property of a target specifies a value of a feature that is not
present in the build request, that value is added.</p></li>
<li class="listitem"><p>Selecting the main target alternative to use. For
each alternative we look how many properties are present both in
alternative's requirements, and in build request. The
alternative with large number of matching properties is selected.
</p></li>
<li class="listitem"><p>Determining "common" properties.
The build request
is <a class="link" href="reference.html#bbv2.reference.variants.proprefine" title="Property refinement">refined</a>
with target's requirements.
The conditional properties in
requirements are handled as well. Finally, default values of
features are added.
</p></li>
<li class="listitem"><p>Building targets referred by the sources list and
dependency properties. The list of sources and the properties
can refer to other target using <a class="link" href="reference.html#bbv2.reference.ids" title="Target identifiers and references">target references</a>. For each
reference, we take all <a class="link" href="reference.html#bbv2.reference.features.attributes.propagated">propagated</a>
properties, refine them by explicit properties specified in the
target reference, and pass the resulting properties as build
request to the other target.
</p></li>
<li class="listitem"><p>Adding the usage requirements produced when building
dependencies to the "common" properties. When dependencies are
built in the previous step, they return
both the set of created
"real" targets, and usage requirements. The usage requirements
are added to the common properties and the resulting property
set will be used for building the current target.
</p></li>
<li class="listitem"><p>Building the target using generators. To convert the
sources to the desired type, Boost.Build uses "generators" ---
objects that correspond to tools like compilers and linkers. Each
generator declares what type of targets it can produce and what
type of sources it requires. Using this information, Boost.Build
determines which generators must be run to produce a specific
target from specific sources. When generators are run, they return
the "real" targets.
</p></li>
<li class="listitem"><p>Computing the usage requirements to be returned. The
conditional properties in usage requirements are expanded
and the result is returned.</p></li>
</ol></div>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="idp262056648"></a>Building a Project</h4></div></div></div>
<p>Often, a user builds a complete project, not just one main
target. In fact, invoking <span class="command"><strong>b2</strong></span> without
arguments
builds the project defined in the current
directory.</p>
<p>When a project is built, the build request is passed without
modification to all main targets in that project.
It's is possible to
prevent implicit building of a target in a project with the
<code class="computeroutput">explicit</code> rule:
</p>
<pre class="programlisting">
explicit hello_test ;
</pre>
<p>
would cause the <code class="computeroutput">hello_test</code> target to be built only if
explicitly requested by the user or by some other target.
</p>
<p>The Jamfile for a project can include a number of
<code class="computeroutput">build-project</code> rule calls that specify additional projects to
be built.
</p>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2006-2009 Vladimir Prus<p>Distributed under the Boost Software License, Version 1.0.
(See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at
<a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div></td>
</tr></table>
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