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<h3><a href="http://www.boost.org/"><img height="86" width="277"
alt="C++ Boost" src="../../../boost.png" border="0"></a></h3>
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<td valign="top">
<h1 align="center">Boost Build System</h1>
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<h2><a name="synopsis" id="synopsis">Synopsis</a></h2>
<p>Boost.Build is a system for large project software construction built on
<a href="../jam_src/index.html">Boost.Jam</a>, a descendant of "<a href=
"http://www.perforce.com/jam/jam.html">Perforce Jam</a>", an open-source
make replacement<a href="#one">[1]</a>. Key features are:</p>
<ul>
<li>A simple target description language</li>
<li>Build with your choice (or multiple) toolsets from a single command
invocation</li>
<li>Build your choice of basic variants (e.g. debug, release, profile...)
and subvariant modifications (e.g. inlining off) from a single command
invocation</li>
<li>``Feature Normalization'' allows target configurations to be
described independently from the toolset used</li>
<li>Modular toolset description files allow build instructions for
different toolsets to be described independently</li>
<li>Multiple subproject support</li>
<li>Automatic building of subproject dependencies</li>
</ul>
<h2><a name="status" id="status">Status</a></h2>Boost.Build v1 is a useful,
mature system. However, its design and structure are not easily adapted to
support some of the features we'd like to see in the future. To this end,
the Boost.Build developers are working on <a href=
"../v2/index.html">Boost.Build v2</a>, which is pretty usable already. If
you are interested in contributing to this effort or you wish to discuss
the design of Boost.Build, please post inquiries to the <a href=
"http://groups.yahoo.com/group/jamboost/">jamboost</a> mailing list at
yahoogroups.
<p><a href="#design_criteria">Here</a> are some of the design criteria that
led to these features.</p>
<h2>Table of Contents</h2>
<ul>
<li><a href="#synopsis">Synopsis</a></li>
<li><a href="#status">Status</a></li>
<li>
<a href="#getting_started">Getting Started</a>
<ul>
<li><a href="#installing_jam">Installing Boost.Jam</a></li>
<li><a href="#initiating">Initiating a Build</a></li>
<li><a href="#setting_variables">Setting Jam Variables</a></li>
<li><a href="#example_jamfile">An Example Jamfile</a></li>
<li><a href="#support_files">Support Files</a></li>
</ul>
</li>
<li>
<a href="#design">Basic Design and Terminology</a>
<ul>
<li><a href="#project_subproject">Projects and Subprojects</a></li>
<li><a href="#targets">Targets</a></li>
<li><a href="#features">Features and Properties</a></li>
<li><a href="#variants">Build Variants</a></li>
<li><a href="#subvariants">Subvariants</a></li>
<li><a href="#dependents">Dependent Targets</a></li>
</ul>
</li>
<li>
<a href="#usage">Usage</a>
<ul>
<li>
<a href="#command_line">The Command-Line</a>
<ul>
<li><a href="#user_targets">User Targets</a></li>
<li><a href="#user_globals">Global Variables</a></li>
</ul>
</li>
<li>
<a href="#subproject_jamfiles">Subproject Jamfiles</a>
<ul>
<li><a href="#subproject_rule">The <tt>subproject</tt>
Rule</a></li>
<li><a href="#main_targets">Describing Main Targets</a></li>
<li><a href="#template_targets">Describing Template
Targets</a></li>
<li><a href="#stage_targets">Describing Stage Targets</a></li>
<li><a href="#jamfile_example">Example</a></li>
</ul>
</li>
<li><a href="#external_project">Using External Projects</a></li>
<li><a href="#requirement_rules">Requirement Rules</a></li>
<li><a href="#install_descriptions">Install Descriptions</a></li>
<li><a href="#feature_description">Feature Descriptions</a></li>
<li><a href="#variant_description">Variant Descriptions</a></li>
<li>
<a href="#toolset_description">Toolset Description Files</a>
<ul>
<li><a href="#toolset_example">Example</a></li>
</ul>
</li>
</ul>
</li>
<li>
<a href="#internals">Internals</a>
<ul>
<li><a href="#target_names">Target Names</a></li>
<li><a href="#internal_globals">Global Variables</a></li>
</ul>
</li>
<li>
<a href="#design_criteria">Design Criteria</a>
<ul>
<li><a href="#assumptions">Assumptions</a></li>
<li><a href="#requirements">Requirements</a></li>
</ul>
</li>
<li><a href="#footnotes">Footnotes</a></li>
</ul>
<h2><a name="getting_started" id="getting_started">Getting Started</a></h2>
<h3><a name="installing_jam" id="installing_jam">Installing
Boost.Jam</a></h3>Follow these <a href=
"../../../more/getting_started.html#step2">instructions</a> to acquire a
bjam executable for your platform. Install it somewhere in your path.
<h3><a name="initiating" id="initiating">Initiating a Build</a></h3>
<p>Boost.Build responds to several global variable settings. The easiest
way to get going is usually to use environment variables, though you can
also set them on the command-line, using
<tt>-s</tt><i>VARIABLE_NAME</i><tt>=</tt><i>value</i>. In addition to the
<a href="../../../more/getting_started.html#step3">toolset configuration
variables</a>, you can use the <tt>TOOLS</tt> variable to indicate which
toolset(s) to build with, and the <tt>BUILD</tt> variable to describe how
you want things built. In many cases it should be sufficient to invoke
<code>bjam</code> with no variable settings.</p>
<p>Some example Boost.Jam invocations:</p>
<table border="1" summary="Sample Jam Invocations=">
<tr>
<th>Command Line(s)</th>
<th>Effects</th>
</tr>
<tr>
<td>
<pre>
bjam -sTOOLS=gcc my_target
</pre>
</td>
<td>default (debug) <tt><a href="#build">BUILD</a></tt> of
<tt>my_target</tt>with GCC</td>
</tr>
<tr>
<td>
<pre>
bjam "-sTOOLS=msvc gcc"
</pre>
</td>
<td>default-build <tt>all</tt> with msvc and gcc</td>
</tr>
<tr>
<td>
<pre>
set TOOLS=msvc
bjam
</pre>
</td>
<td>Set an NT environment variable to always build with MSVC<br>
default-build <tt>all</tt>.</td>
</tr>
<tr>
<td>
<pre>
bjam "-sBUILD=release &lt;debug-symbols&gt;on"
</pre>
</td>
<td>release build with debug symbols of <tt>all</tt> using default
<tt><a href="#tools">TOOLS</a></tt></td>
</tr>
<tr>
<td>
<pre>
bjam "-sBUILD=debug release"
</pre>
</td>
<td>debug and release build <tt>all</tt>.</td>
</tr>
<tr>
<td><code>set TOOLS=msvc<br>
bjam "-sBUILD=&lt;cxxflags&gt;-G6"<br>
&nbsp;</code></td>
<td>Set an NT environment variable to always build with MSVC<br>
default-build <tt>all</tt>, adding a compiler command line switch</td>
</tr>
<tr>
<td><code>set TOOLS=msvc gcc<br>
bjam "-sBUILD=&lt;msvc&gt;&lt;*&gt;&lt;cxxflags&gt;-G6"<br>
&nbsp;</code></td>
<td>Set an NT environment variable to always build with MSVC and
GCC<br>
default-build <tt>all</tt>, adding a MSVC-specific compiler command
line switch</td>
</tr>
<tr>
<td><code>bjam "-sBUILD=&lt;define&gt;BOOST_POSIX"</code></td>
<td>build all, with the macro BOOST_POSIX defined for all
compilers</td>
</tr>
</table>
<h3><a name="setting_variables" id="setting_variables">Setting Jam
Variables</a></h3>
<p>The "<tt>-s</tt>" options in the command lines above are passing
variable settings to the build system. There are actually three ways to do
that:</p>
<ul>
<li>Jam picks up variable settings from your environment by default, so
you can set them there:
<blockquote>
<pre>
&gt; <a href="#build">BUILD</a>="debug release" <i># assuming Unix</i>
&gt; export <a href="#build">BUILD</a>
&gt; bjam ...
</pre>
</blockquote>This approach can be OK for quick-and-dirty tests, but
environment variable settings tend to be unstable and non-uniform
across users and machines, so it's best not to rely on the environment
much.
</li>
<li>Explicitly on the command-line, with the "<tt>-s</tt>" option.</li>
<li>Directly in Jam code. A project's <a href="#jamrules">Jamrules</a>
file is a convenient place to make global settings.</li>
</ul>
<h3><a name="example_jamfile" id="example_jamfile">An Example
Jamfile</a></h3>Here is an example of a simple subproject Jamfile. In this
example, it is assumed that the user has set <tt>BOOST_ROOT</tt>, either as
an environment variable, on the command-line or in the project's
<tt><a href="#jamrules">Jamrules</a></tt> file:
<blockquote>
<pre>
subproject foo/bar/baz ; # path to here from project root
# A static library called 'baz'
lib baz : baz1.cpp baz2.cpp # C++ sources
parser/src/baz4.ll # Lex-&gt;C++ sources
parser/src/baz5.yy # Yacc-&gt;C++ sources
: &lt;include&gt;$(BOOST_PARENT_DIRECTORY) # Put boost in #include path
;
# An executable called 'test'
exe test : &lt;lib&gt;baz # use the 'baz' library
baz_test.cpp # C++ source
: &lt;include&gt;$(BOOST_ROOT)
;
</pre>
</blockquote>
<p>That's it! The build system takes care of the rest. If the you want to
be able to build all subprojects from the project root directory, you can
add a Jamfile at the root:</p>
<blockquote>
<pre>
project-root ; # declare this to be the project root directory
# Read subproject Jamfiles
subinclude foo/bar/baz <font color="#7F7F7F">foo/bar/...</font> ;
<font color="#7F7F7F">subinclude a/b/c ...</font> ; # more subincludes
</pre>
</blockquote>
<h3><a name="support_files" id="support_files">Support Files</a></h3>
<p>To use the build system, the following must be located in your project's
root directory, or in a directory specified in the
<tt>BOOST_BUILD_PATH</tt> variable. It is usually convenient to specify the
<tt>BOOST_BUILD_PATH</tt> in your project's <a href=
"#jamrules">Jamrules</a> file. The <a href="../../../Jamrules">Boost
Jamrules</a> file shows an example.</p>
<table border="1" summary="Support Files">
<tr>
<th>Filename(s)</th>
<th>Meaning</th>
</tr>
<tr>
<td><i>toolset</i><tt>-tools.jam</tt></td>
<td>Feature-to-command-line mapping for <i>toolset</i>.</td>
</tr>
<tr>
<td><tt>features.jam</tt></td>
<td>Abstract toolset feature descriptions.</td>
</tr>
<tr>
<td><tt>boost-base.jam</tt></td>
<td>Boost build system-specific rule definitions.</td>
</tr>
<tr>
<td><tt>unit-tests.jam</tt></td>
<td>Unit tests and assertions for boost Jam code.</td>
</tr>
</table>The <tt>boost-base.jam</tt> file is temporary, and will eventually
be compiled into our Jam executable.
<h2><a name="design" id="design">Basic Design and Terminology</a></h2>This
section gives an overview of the way that the system works, outlining the
system's capabilities and overall design. It also introduces the
terminology and concepts necessary to understand the sections on writing
Jamfiles and command-line invocations.
<h3><a name="project_subproject" id="project_subproject">Projects and
Subprojects</a></h3>
<p>A <b>project</b> is a source directory tree containing at least one
<tt>Jamfile</tt>. The root directory of the project is known as the
<b>project root</b>. <a name="jamrules" id="jamrules">The</a> root
directory of a project may contain a <tt>Jamrules</tt> file, which contains
project-specific Jam code. If the <tt>Jamrules</tt> file is not present
when Jam is invoked, a warning will be issued.</p>
<p>Subdirectories containing <tt>Jamfile</tt>s are called <b>subproject
directories</b>. Each such <tt>Jamfile</tt> describes a
<b>subproject</b>.</p>
<p>The <b>build system installation directory</b> is a directory containing
Jam files describing compilers and build variants. The installation
directory can be specified in a file called <tt>boost-build.jam</tt> in the
project root directory. This file should contain a line <tt>boost-build
$path-to-installation-dir</tt>. If no such file is available the
environment variable <tt>BOOST_BUILD_PATH</tt> will be used. This lists a
set of directories to search for the files comprising the build system. If
the installation directory is not specified, it is the same as the project
root, and <tt>BOOST_BUILD_PATH</tt> is set to include that directory.</p>
<h3><a name="targets" id="targets">Targets</a></h3>
<p>Each <tt>Jamfile</tt> describes one or more <b>main targets</b>.</p>
<p>Each main target is an abstract description of one or more <b>built
targets</b> which are expressions of the corresponding main target under
particular compilers and build variants. Intermediate files such as
<tt>.o</tt>/<tt>.obj</tt> files generated by compiling <tt>.cpp</tt> files
as a consequence of building a main target are also referred to as built
targets. The term <b>build directory tree</b> refers to the location of
built target files.</p>
<ul>
<li>By default, the build directory tree is overlaid with the project
directory tree, with targets generated into a subtree rooted at the
<tt>bin</tt> subdirectory of each subproject directory (the name of this
directory can be customized by changing the <tt>BIN_DIRECTORY</tt>
variable.</li>
<li><a name="all_locate_target" id="all_locate_target">If the variable
<tt>ALL_LOCATE_TARGET</tt> is set</a>, it specifies an alternate build
directory tree whose structure mirrors that of the project. In this case,
built targets of a subproject are generated into the corresponding
directory of the build directory tree.</li>
</ul>For each main target, there is a corresponding location in the build
directory tree known as the target's <b>build root</b>, where all
intermediate and final targets resulting from that main target are located.
<h3><a name="features" id="features">Features and Properties</a></h3>
<p>A <b>feature</b> is a normalized (toolset-independent) description of an
individual build parameter, such as whether inlining is enabled. Each
feature usually corresponds to a command-line option of one or more build
tools. Features come in four varieties:</p>
<ol>
<li><b>Simple features</b> can take on any of several predetermined
values. For example, the feature <tt>optimization</tt> might take one of
the values <tt>off</tt>, <tt>speed</tt>, or <tt>space</tt>. Simple
features have a default value. The key aspect of simple features is that
they are assumed to affect link compatibility: object files generated
with different values for a simple feature are generated into a separate
directories, and (with a few exceptions) main targets generated with
different values won't be linked together.</li>
<li><b>Free features</b> can either be single-valued, as above, or may
take on any number of user-specified values simultaneously. For example,
the <tt>define</tt> feature for a release build might have the values
<tt>NDEBUG</tt> and <tt>BOOST_RELEASE_BUILD</tt>. Free features are
assumed not to affect link compatibility.</li>
<li><b>Path features</b> are free features whose values describe paths
which may be relative to the subproject (such as linked libraries or
<tt>#include</tt> search directories). The build system treats the values
of these features specially to ensure that they are interpreted relative
to the subproject directory regardless of the directory where Jam was
invoked.</li>
<li><b>Dependency features</b> are path features whose values describe a
dependency of built targets. For example, an external library might be
specified with a dependency-feature: if the library is updated, the
target will be updated also. The <tt>&lt;library-file&gt;</tt> feature
works this way <a href="#two">[2]</a>.</li>
</ol>
<p>A feature-value pair is known as a <b>build property</b>, or simply
<b>property</b>. The prefixes <i>simple</i>, <i>free</i>, <i>path</i>, and
<i>dependency</i> apply to properties in an analogous way to features.</p>
<h3><a name="variants" id="variants">Build Variants</a></h3>
<p>A build variant, or simply <b>variant</b> is a named set of build
properties describing how targets should be built. Typically you'll want at
least two separate variants: one for debugging, and one for your release
code.</p>
<p>Built targets for distinct build variants and toolsets are generated in
separate parts of the build directory tree, known as the <b>variant
directories</b>. For example, a (sub)project with main targets <tt>foo</tt>
and <tt>bar</tt>, compiled with both GCC and KAI for <tt>debug</tt> and
<tt>release</tt> variants might generate the following structure (target
directories in <b>bold</b>).</p>
<blockquote>
<pre>
bin
+-foo <font color="#7F7F7F">&lt;--- foo's build root</font>
| +-gcc
| | +-<b>debug</b>
| | `-<b>release</b>
| `-kai
| +-<b>debug</b>
| `-<b>release</b>
`-bar <font color="#7F7F7F">&lt;--- bar's build root</font>
+-gcc
| +-<b>debug</b>
| `-<b>release</b>
`-kai
+-<b>debug</b>
`-<b>release</b>
</pre>
</blockquote>
<p>The properties constituting a variant may differ according to toolset,
so <tt>debug</tt> may mean a slightly different set of properties for two
different compilers.</p>
<h3><a name="subvariants" id="subvariants">Subvariants</a></h3>
<p>When a target is built with <i>simple</i> properties that don't exactly
match those specified in a build variant, the non-matching features are
called <b>subvariant features</b> and the target is located in a
<b>subvariant directory</b> beneath the directory of the base variant. This
can occur for two reasons:</p>
<ol>
<li>Some features are only relevant to certain compilers. When relevant
simple features have no value specified in the build variant, a value
must be chosen. Even when the default value is used, the target is
generated into a subvariant directory. For example, the
<tt>runtime-link</tt> feature may be unspecified in the <tt>debug</tt>
variant, but relevant to MSVC. In that case, a fragment of the target
tree might look like:
<blockquote>
<pre>
bin
+-foo <font color="#7F7F7F">&lt;--- foo's build root</font>
| +-msvc
| | +-debug
. . . `-<b>runtime-link-dynamic</b>
. . .
</pre>
</blockquote>Because the default value of <tt>runtime-link</tt> is
<tt>dynamic</tt>, when the <tt>debug</tt> variant is requested, the
<tt>runtime-link-dynamic</tt> subvariant of foo is built.<br>
<br>
</li>
<li>It is possible to request (either on the command-line, or as part of
a main target description) that particular subvariants be built. For
example, it may be desirable to generate builds that link to the runtime
both statically <i>and</i> dynamically. In that case, both subvariant
directories in the example above would be generated:
<blockquote>
<pre>
bin
+-foo <font color="#7F7F7F">&lt;--- foo's build root</font>
| +-msvc
| | +-debug
. . . +-<b>runtime-link-dynamic</b>
. . . `-<b>runtime-link-static</b>
. . .
</pre>
</blockquote>
</li>
</ol>In no case will targets be built directly into
<tt>bin/foo/msvc/debug</tt>, since the <tt>debug</tt> variant doesn't
include the <tt>runtime-link</tt> feature, which is relevant to MSVC.
<p>When a subvariant includes multiple subvariant features, targets are
built into a subvariant directory whose path is determined by concatenating
the properties sorted in order of their feature names. For example, the
borland compiler, which uses different libraries depending on whether the
target is a console or GUI program, might create the following structure
for a DLL:</p>
<blockquote>
<pre>
bin
+-foo <font color="#7F7F7F">&lt;--- foo's build root</font>
| +-msvc
| | +-debug
| | | +-runtime-link-dynamic
| | | | +-<b>user-interface-console</b>
| | | | `-<b>user-interface-gui</b>
. . . `-runtime-link-static
. . . +-<b>user-interface-console</b>
. . . `user-interface-gui
</pre>
</blockquote>
<p>Any configuration of properties for which a target is built, whether
base variant or subvariant, is known as a <b>build configuration</b>, or
simply a <b>build</b>.</p>
<h3><a name="dependents" id="dependents">Dependent Targets</a></h3>
<p>When a main target depends on the product of a second main target (as
when an executable depends on and links to a static library), each build
configuration of the dependent target is depends on the
<i>corresponding</i> build of the dependency. Because only simple features
participate in build identity, the dependent and dependency targets may
have completely different free features. This puts the onus on the user for
ensuring link-compatibility when certain free properties are used. For
example, when <tt>assert()</tt> is used in header files, the preprocessor
symbol <tt>NDEBUG</tt> can impact link-compatibility of separate
compilation units. This danger can be minimized by encapsulating such
feature differences inside of build variants.</p>
<h2><a name="usage" id="usage">Usage</a></h2>
<p>This section describes how to start a build from the command-line and
how to write project and subproject Jamfiles. It also describes the other
files written in the Jam language: build-tool specification files, feature
descriptions files.</p>
<h3><a name="command_line" id="command_line">The Command Line</a></h3>
<p>This section describes in detail how the build system can be
invoked.</p>
<h4><a name="user_targets" id="user_targets">User Targets</a></h4>
<p>The Jam command line ends with an optional list of target names; if no
target names are supplied, the built-in pseudotarget <tt>all</tt> is built.
In a large project, naming targets can be dicey because of collisions. Jam
uses a mechanism called grist to distinguish targets that would otherwise
have the same name. Fortunately, you won't often have to supply grist at
the command-line. When you declare a main target, a Jam pseudotarget of the
same name is created which depends on <i>all</i> of the subvariants
requested for your invocation of the build system. For example, if your
subproject declares:</p>
<blockquote>
<pre>
exe my_target : my_source1.cpp my_source2.c ;
</pre>
</blockquote>and you invoke Jam with <tt>-sBUILD="debug
release"&nbsp;my_target</tt>, you will build both the debug and release
versions of <tt>my_target</tt>.
<p>These simple, ungristed names are called <b>user targets</b>, and are
only available for the subproject where Jam is invoked. That way, builds
from the top level (which may include many Jamfiles through the subinclude
rule) and builds of library dependencies (which may live in other
subprojects), don't collide. If it is necessary to refer more explicitly to
a particular target from the command-line, you will have to add ``grist''.
Please see <a href="#target_names">this section</a> for a more complete
description of how to name particular targets in a build.</p>
<h4><a name="user_globals" id="user_globals">Global Variables</a></h4>
<p>This is a partial list of global variables that can be set on the
command-line. Of course you are free to write your own Jam rules which
interpret other variables from the command-line. This list just details
some of the variables used by the build system itself. Note also that if
you don't like the default values you can override them in your project's
<tt><a href="#jamrules">Jamrules</a></tt> file.</p>
<table border="1" summary="User Globals">
<tr>
<th>Variable <!-- <th>Meaning --></th>
<th>Default</th>
<th>Example</th>
<th>Notes</th>
</tr>
<tr>
<td rowspan="2"><tt><a name="tools" id="tools">TOOLS</a></tt>
<!-- <td rowspan="2">Toolsets to build with --></td>
<td rowspan="2">Platform-dependent</td>
<td><tt>"-sTOOLS=gcc&nbsp;msvc"</tt></td>
<td>build with gcc and msvc</td>
</tr>
<tr>
<td><tt>-sTOOLS=gcc</tt></td>
<td>build with gcc</td>
</tr>
<tr>
<td rowspan="4"><tt><a name="build" id="build">BUILD</a></tt>
<!-- <td rowspan="4">Build configuration (see -->
<!-- <a href="#default_build">here</a>). --></td>
<td rowspan="4"><tt>debug</tt></td>
<td><tt>-sBUILD=release</tt></td>
<td>build the <tt>release</tt> variant</td>
</tr>
<tr>
<td><tt>"-sBUILD=debug release"</tt></td>
<td>build both <tt>debug</tt> and <tt>release</tt> variants</td>
</tr>
<tr>
<td><tt>"-sBUILD=&lt;optimization&gt;speed"</tt></td>
<td>build a subvariant of the default variant (<tt>debug</tt>) with
optimization for speed.</td>
</tr>
<tr>
<td><tt>"-sBUILD=debug release
&lt;runtime-link&gt;static/dynamic"</tt></td>
<td>build subvariants of the debug and release variants that link to
the runtime both statically and dynamically.</td>
</tr>
<tr>
<td><tt>ALL_LOCATE_TARGET</tt>
<!-- <td>Alternate location for built targets (see <a -->
<!-- href="#all_locate_target">here</a>) --></td>
<td><i>empty</i></td>
<td><tt>-sALL_LOCATE_TARGET=~/build</tt></td>
<td>Generate all build results in the <tt>build</tt> subdirectory of
the user's home directory (UNIX).</td>
</tr>
</table>This section describes how to write a Jamfile for a subproject.
<h3><a name="subproject_jamfiles" id="subproject_jamfiles">SubProject
Jamfiles</a></h3>
<h4><a name="subproject_rule" id="subproject_rule">The <tt>subproject</tt>
rule</a></h4>
<p>A subproject's Jamfile begins with an invocation of the
<tt>subproject</tt> rule that specifies the subproject's location relative
to the top of the project tree:</p>
<blockquote>
<pre>
subproject <i>path-from-top</i> ;
</pre>
</blockquote>
<p>The <tt>subproject</tt> rule tells the build system where to place built
targets from the subproject in case <tt>ALL_LOCATE_TARGET</tt> is used to
specify the build directory tree. If there is a Jamfile in the project root
directory, you should use the <tt>project-root</tt> rule instead:</p>
<blockquote>
<pre>
project-root ;
</pre>
</blockquote>
<h4><a name="main_targets" id="main_targets">Describing Main
Targets</a></h4>
<p>A main target is described using the following syntax:</p>
<blockquote>
<pre>
<i>target-type</i> <i>name</i> : <i>sources</i>
[ : <i>requirements</i> [ : <i><a href=
"#default_build">default-BUILD</a></i> ] ] ;
</pre>
</blockquote>
<ul>
<li><i>target-type</i> may be one of <tt>exe</tt>, <tt>lib</tt>,
<tt>dll</tt>, <tt>stage</tt> or <tt>template</tt>. These are actually
names of Jam rules. Additional main target rules are possible; see
<tt><a href="../../../status/Jamfile">status/Jamfile</a></tt> or
<tt><a href=
"../../../libs/python/build/Jamfile">libs/python/build/Jamfile</a></tt>
for examples.<br>
<br></li>
<li><i>name</i> specifies the name of the main target, multiple targets
with the same name are allowed but only if they are of different types.
Normally this is not the name of the final target file generated. The
target file name depends on the type of target which controls how the
base target name is renamed to conform to platform conventions. For
<tt>exe</tt>s the name might be the same or <tt>*.exe</tt>. For
<tt>lib</tt>s the name might be <tt>*.lib</tt> or <tt>lib*.a</tt>. And
for <tt>dll</tt>s the name might be <tt>*.dll</tt> or <tt>lib*.so</tt>.
For platform specific naming consult the <tt><a href=
"allyourbase.jam">allyourbase.jam</a></tt> file in the build system.<br>
<br></li>
<li>
<i>sources</i> is a list of paths to source files and dependency
targets. <a name="dependency" id="dependency">The</a> syntax for
dependency targets is described by the following grammar:
<blockquote>
<pre>
<i>dependency-target</i> -&gt; <i>type-tag</i> <i>location</i> <b>target-name</b>
<i>type-tag</i> -&gt; "&lt;template&gt;" | "&lt;lib&gt;" | "&lt;dll&gt;" | "&lt;exe&gt;"
<i>location</i> -&gt; ( @<b>project-id</b>/ )? <i>relative-path</i>
<i>relative-path</i> -&gt; ( <b>path-element</b>/ ) *
</pre>
</blockquote>The <i>location</i> specifies the location of a Jamfile in
which a dependency target called <code><b>target-name</b></code> can be
found, declared with the given <i>type-tag</i>. Other <i>type-tag</i>s
are possible; for example the <a href="python.jam">python.jam</a>
module defines Python extensions with the <code>"&lt;pyd&gt;"</code>
tag. If <code>@<b>project-id</b></code> is specified, the
<i>relative-path</i> is interpreted with respect to the root directory
of the <a href="#external_project">specified project</a>. Otherwise, it
is interpreted with respect to the directory of the current Jamfile.
<p>The dependency's <i>type-tag</i> is also used to decide how to link
to it when needed. <tt>&lt;lib&gt;</tt> targets are linked statically
and <tt>&lt;dll&gt;</tt> targets are linked dynamically. On Unix
platforms dynamic linking will use (the appropriate platform equivalent
of) <tt>LD_LIBRARY_PATH</tt> and the "<tt>-l</tt>" linker flag to avoid
creating executables which expect to find dynamic libraries in
particular locations in the filesystem.</p>
<p><b>NOTE:</b> It is important to match the <i>type-tag</i> dependency
with the type of the dependency target. Trying to specify a
<i>type-tag</i> of <tt>&lt;lib&gt;</tt> when the target is defined as a
<tt>&lt;dll&gt;</tt> will cause an error.</p><br>
</li>
<li>
<i><a name="target_requirements" id=
"target_requirements">requirements</a></i> specifies the build
properties intrinsic to the target. Requirements are given as sets of
optionally-<b>qualified build properties</b>:
<blockquote>
<pre>
[[&lt;<i>compiler</i>&gt;]&lt;<i>variant</i>&gt;]&lt;<i>feature</i>&gt;<i>value</i>
</pre>
</blockquote><tt>&lt;<i>compiler</i>&gt;</tt> and
<tt>&lt;<i>variant</i>&gt;</tt>, if supplied, can be used to restrict
the applicability of the requirement. Either one may be replaced by
<tt>&lt;*&gt;</tt>, which is the same as omitting it.
<p>The system checks that simple feature requirements are not violated
by explicit subvariant build requests, and will issue a warning
otherwise. Free features specified as requirements are simply added to
each corresponding build configuration.</p><br>
</li>
<li>
<i><a name="default_build" id="default_build">default-BUILD</a></i>
specifies the configurations that should be built if the <tt><a href=
"#build">BUILD</a></tt> variable is not otherwise specified. Any
elements not beginning with ``<tt>&lt;</tt>...<tt>&gt;</tt>'' refer to
build variants. Other elements use the same syntax as the <a href=
"#target_requirements">requirements</a> described above, except that
multiple values may be specified for a simple feature by separating
them with a slash, forming (qualified) <b>multi-valued properties</b>:
<blockquote>
<pre>
[[&lt;<i>compiler</i>&gt;]&lt;<i>variant</i>&gt;]&lt;<i>feature</i>&gt;<i>value1</i>[/<i>value2</i>...]
</pre>
</blockquote>When multiple values are specified, it causes <i>all</i>
the implied configurations to be built by default. It is also possible
to prevent any default builds from occurring on this target by using
<code>&lt;suppress&gt;true</code> . This suppresses any local targets,
either implicit or explicit, from building. But, this does not prevent
implied targets as required by a dependency by another target to this
one from being built. This is useful, for example, for defining a set
of libraries generically and having them built only when another target
like an exe is built. Such use might look like:
<blockquote>
<pre>
lib basic : basic.cpp : : &lt;suppress&gt;true ;<br>
<br>
exe test : test.cpp &lt;lib&gt;basic ;
</pre>
</blockquote>With that the <tt>basic</tt> library will only be built
when the <tt>test</tt> executable is built, and only the variations
required by the executable will be built.<br>
</li>
</ul>
<p><b>NOTE:</b> for simple features in both <i><a href=
"#target_requirements">requirements</a></i> and <i><a href=
"#default_build">default-BUILD</a></i>, more-specific qualification
overrides less-specific.</p>
<h4><a name="template_targets" id="template_targets">Describing Template
Targets</a></h4>
<p>Template targets provide a way to handle commonalities between projects
targets. They have the same form as <a href="#main_targets">main
targets</a> but do not initiate build requests. A target that lists a
template as a dependency inherits all the settings from the template, i.e.
the templates sources, requirements and default build settings will be
added to the targets settings. Paths mentioned in a template definition are
always relative to the subdirectory of the Jamfile containing the templates
definition, regardless of the subdirectory of the dependent main target.
Typically a project will have at least one template target that handles
defines, include paths and additional compiler flags common to all targets
in the project.</p>
<h4><a name="stage_targets" id="stage_targets">Describing Stage
Targets</a></h4>
<p>Stage targets are a special kind of target that don't build a single
file but to a collection of files. The goal is to create a directory which
is composed of the various files that other targets generate, or individual
files. When built a stage target creates a directory with the same name as
the target, and copies the dependent files to it. The form of the target is
the same as that of <a href="#main_targets">main targets</a> with some
differences...</p>
<ul>
<li><i>target-type</i> is <tt>stage</tt>. See <tt><a href=
"../../../libs/regex/build/Jamfile">libs/regex/build/Jamfile</a></tt> for
an example.<br>
<br></li>
<li><i>Name</i> specifies the name of the stage and is the name of the
directory created.<br>
<br></li>
<li><i>sources</i> is the same as main targets and one can list both
generated targets like <tt>&lt;exe&gt;test_exe</tt> and individual files,
but not template targets.<br>
<br></li>
<li>
<i>Requirements</i> the build properties specified are used as with
main targets. But one additional type of requirement is possible:
<tt>&lt;tag&gt;</tt>... A tag specifies how to "augment" the names of
the copied files. This is needed to distinguish the various files if
you're collecting different builds of the same targets. The syntax is:
<blockquote>
<pre>
&lt;tag&gt;&lt;<i>feature|variant</i>&gt;<i>value</i>
</pre>
</blockquote><br>
If the <tt><i>feature</i></tt> or <tt><i>variant</i></tt> is present
for the a target the file for that target is renamed to include the
given <tt><i>value</i></tt> between the basename and the suffix. Two
special <tt>tag</tt>s, <tt>&lt;tag&gt;&lt;prefix&gt;</tt> and
<tt>&lt;tag&gt;&lt;postfix&gt;</tt>, let one prepend and append a value
to the "augmentation" respectively.<br>
<br>
</li>
<li><i>default-BUILD</i> acts in the same manner as a main
target.<br></li>
</ul>
<h4><a name="jamfile_example" id="jamfile_example">Example</a></h4>
<p>This artificially complex example shows how two executables called "foo"
and "fop" might be described in a Jamfile. All common settings are factored
out in the templates "base" and "executable". Foo is composed of the
sources <tt>./foo.cpp</tt> and <tt>./src/bar.cpp</tt> (specified relative
to the directory in which the Jamfile resides). Fop only has one sourcefile
<tt>./fop.cpp</tt>. Both executables link against the built target which
results from building the target <tt>baz</tt> as described in
<tt>../bazlib/Jamfile</tt>.</p>
<blockquote>
<pre>
template base :
## <a href="#target_requirements">Requirements</a> ##
: &lt;include&gt;../bazlib/include
&lt;define&gt;BUILDING_FOO=1
&lt;release&gt;&lt;define&gt;FOO_RELEASE
&lt;msvc&gt;&lt;*&gt;&lt;define&gt;FOO_MSVC
&lt;msvc&gt;&lt;release&gt;&lt;define&gt;FOO_MSVC_RELEASE
&lt;gcc&gt;&lt;*&gt;&lt;optimization&gt;off
&lt;gcc&gt;&lt;release&gt;&lt;optimization&gt;space
&lt;threading&gt;multi
&lt;sysinclude&gt;/usr/local/foolib/include
## <a href="#default_build">default-BUILD</a> ##
: debug release
&lt;debug&gt;&lt;runtime-link&gt;static/dynamic
;
template executable : &lt;template&gt;base &lt;lib&gt;../bazlib/baz ;
exe foo : &lt;template&gt;executable foo.cpp src/bar.cpp ;
exe fop : &lt;template&gt;executable fop.cpp ;
</pre>
</blockquote>
<p>The <a href="#target_requirements">requirements</a> section:</p>
<ul>
<li>Adds <tt>../bazlib/include</tt> to the <tt>#include</tt> path</li>
<li>Sets the preprocessor symbol <tt>BUILDING_FOO</tt> to <tt>1</tt></li>
<li>In the <tt>release</tt> builds, <tt>#define</tt>s
<tt>FOO_RELEASE</tt>.</li>
<li>When built with MSVC, <tt>#define</tt>s <tt>FOO_MSVC</tt>.</li>
<li>In <tt>release</tt> variants built with MSVC, <tt>#define</tt>s
<tt>FOO_MSVC_RELEASE</tt>.</li>
<li>Most builds under GCC have optimization turned off, but...</li>
<li>...GCC <tt>release</tt> builds require optimization for space.</li>
<li>Requires multithread support on compilers where it's relevant.</li>
<li>Adds <tt>/usr/local/foolib/include</tt> to the <tt>#include
&lt;*&gt;</tt> path</li>
</ul>
<p>The <a href="#default_build">default-BUILD</a> section:</p>
<ul>
<li>specifies that <tt>debug</tt> and <tt>release</tt> base variants are
built by default.</li>
<li>on compilers where the feature is relevant, requests both statically-
and dynamically-linked subvariants of the debug variant.</li>
</ul>
<h3><a name="external_project" id="external_project">Using External
Projects</a></h3>To use dependencies such as libraries from another project
tree, first use the <code>project</code> rule to declare a project id and
location for the external project. Then add the appropriate external
<a href="#dependency">dependency target specification</a> to your program's
list of sources. For example, if you are developing a program which uses
the Boost.Threads library, you might write
<blockquote>
<pre>
project boost : /home/dave/boost-cvs ;
</pre>
</blockquote>in your <a href="#jamrules">Jamrules</a> file, and place
<blockquote>
<pre>
&lt;dll&gt;@boost/libs/thread/build/boost_thread
</pre>
</blockquote>in your target's list of sources.
<h3><a name="requirement_rules" id="requirement_rules">Requirement
Rules</a></h3>
<p>Target requirements support the use of auxiliary rules to allow for more
complex decisions about the requirements. If specified, by using the name
of a rule in the requirements, the rule is called with the signature: <tt>(
toolset variant : subvariant-path properties * )</tt> and should return the
modified set of properties. There are a number of built-in rules for some
common tasks that Boost uses, and you can use:</p>
<blockquote>
<table border="1" summary="Built In Requirement Rules">
<tr>
<th>Rule</th>
<th>Effects</th>
</tr>
<tr>
<td><tt>std::locale-support</tt></td>
<td>Ensures that locale support is available for the target. For
example some toolsets, like CodeWarrior, locale support is only
available on specific platforms using a static runtime.</td>
</tr>
<tr>
<td><tt>std::facet-support</tt></td>
<td>Ensures that facet support is available for the target.</td>
</tr>
<tr>
<td><tt>common-variant-tag</tt></td>
<td>
<p>Adds a constructed prefix tag to the target to conform to the
Boost common naming conventions for libraries. The tag is
constructed as:</p>
<blockquote>
[-&lt;toolset-tag&gt;][-&lt;thread-tag&gt;][-&lt;runtime-tag&gt;][-&lt;version-tag&gt;]
</blockquote>
<ul>
<li>&lt;toolset-tag&gt; maps to an abbreviated name of the
toolset and when possible, and applicable, the version of the
toolset.</li>
<li>&lt;thread-tag&gt; "mt" when multi-threading is enabled.</li>
<li>&lt;runtime-tag&gt; adds these single letter tags:<br>
&nbsp;&nbsp;"s" when static linking to runtime<br>
&nbsp;&nbsp;"g" when linking to debug runtime<br>
&nbsp;&nbsp;"y" when building debug-python variants<br>
&nbsp;&nbsp;"d" when building debug variants<br>
&nbsp;&nbsp;"p" when building with stlport libraries<br>
&nbsp;&nbsp;"n" when building with stlport and using native
iostreams</li>
<li>&lt;version-tag&gt; adds "major_minor" from a
<tt>&lt;version&gt;</tt> property. Defaults to using
$(BOOST_VERSION) if no version property is present.</li>
</ul>
</td>
</tr>
</table>
</blockquote>
<h3><a name="install_descriptions" id="install_descriptions">Install
Descriptions</a></h3>
<p>Installable files and targets are described with:</p>
<blockquote>
<pre>
install <i>name</i> <i>type</i> : <i>sources</i>... : [<i>options</i>]... ;
</pre>
</blockquote>
<p>Install descriptions define files and targets that can be installed by
use of a <tt>stage</tt> target.</p>
<ul>
<li><i>name</i> specifies the name to group the given files and targets
as a collective entity. Multiple <tt>install</tt> descriptions can use
the same name, in which case they are all collected into a single
group.<br>
<br></li>
<li><i>type</i> indicates the type of files specified by the
<tt>install</tt>. This is used to later install files from different
groups but with the same type.<br>
<br></li>
<li><i>sources</i> can list both generated targets like
<tt>&lt;exe&gt;test_exe</tt> and individual files, but not template
targets.<br>
<br></li>
<li><i>options</i> additional options, currently none defined.<br></li>
</ul>
<p>Install descriptions are meant to be used by <tt>stage</tt> targets to
collect the various sources of many install descriptions into one or more
destination directories. For this there are two rules that help in getting
the sources specified:</p>
<ul>
<li><tt>install-subinclude <i>jamfiles</i>... :
[<i>options</i>]...</tt><br>
<br>
Includes the listed Jamfiles to read in the install descriptions.
Multiple <tt>&lt;exclude&gt;<i>name</i></tt> options can be used to
exclude the named groups of install descriptions from getting
defined.<br>
<br></li>
<li><tt>install-source <i>type</i></tt><br>
<br>
Returns the list of sources and targets specified by the install for the
given type. The returned list can be used as the sources for a
<tt>stage</tt> target which would place all the sources into that
stage.<br>
<br></li>
</ul>
<h3><a name="feature_description" id="feature_description">Feature
Descriptions</a></h3>
<p>Features are described by stating the feature type (simple features are
specified with "<tt>feature</tt>"), followed by the feature name. An
optional second argument can be used to list the permissible values of the
feature. Examples can be found in <a href=
"features.jam">features.jam</a>.</p>
<h3><a name="variant_description" id="variant_description">Variant
Descriptions</a></h3>
<p>Variants are described with the following syntax:</p>
<blockquote>
<pre>
variant <i>name</i> [ : parent-name] : [&lt;<i>toolset-name</i>&gt;]&lt;<i>feature</i>&gt;value... ;
</pre>
</blockquote>The <tt>variant</tt> rule specifies the list of properties
comprising a variant. Properties may be optionally qualified with a toolset
name, which specifies that the property applies only to that toolset. One
or more parent variants may be specified to inherit the properties
&nbsp;from those parent(s). For inherited properties precedence is given on
a left to right order, making the immediate properties override those in
the parent(s). This can be used to great effect for describing global
properties that are shared amongst various variants, and therefore targets.
For example:
<blockquote>
<pre>
variant my-globals : &lt;rtti&gt;off ;
variant my-debug : my-globals debug ;
variant my-release : my-globals release ;
</pre>
</blockquote>More examples can be found in <a href=
"features.jam">features.jam</a>.
<h3><a name="toolset_description" id="toolset_description">Toolset
Description Files</a></h3>
<p>Toolset descriptions are located in the project's root directory, or a
directory specified by <tt>BOOST_BUILD_INSTALLATION</tt>, which may be set
in a <tt>Jamfile</tt> or the project's <tt><a href=
"#jamrules">Jamrules</a></tt> file. Each file is called
<i>toolset-name</i><tt>-tools.jam</tt>, where <i>toolset-name</i> is the
name of the toolset. The toolset description file has two main jobs:</p>
<ol>
<li>redefine the following rules:
<ul>
<li><tt>Link-action</tt> - links an executable from objects and
libraries</li>
<li><tt>Archive-action</tt> - links a static library from object
files</li>
<li><tt>C++-action</tt> - compiles a 'C++' file into an object
file</li>
<li><tt>Cc-action</tt> - compiles a 'C' file into an object file</li>
</ul>These rules should simply invoke the action part of a rule whose
name is uniquely defined for the toolset. For example,
<blockquote>
<pre>
rule C++-action
{
msvc-C++-action $(&lt;) : $(&gt;) ;
}
actions msvc-C++-action
{
cl -nologo -GX -c -U$(UNDEFS) -D$(DEFINES) $(CFLAGS) $(C++FLAGS) -I$(HDRS) -I$(STDHDRS) -Fo$(&lt;) -Tp$(&gt;)
}
</pre>
</blockquote>Note that <tt>Link-action</tt> may require special care:
on platforms where the global variable <tt>gEXPORT_SUFFIX(DLL)</tt> is
defined (e.g. Windows), the first argument may have two elements when
linking a shared library. The first is the shared library target, and
the second is the import library target, with suffix given by
<tt>$(gEXPORT_SUFFIX(DLL))</tt>. It will always have a third argument
which is either ``<tt>EXE</tt>'' or ``<tt>DLL</tt>''. This can be used
to dispatch to different actions for linking DLLs and EXEs if
necessary, but usually it will be easier to take advantage of the
special <tt>&lt;target-type&gt;</tt> feature, which will have the same
value using the <tt>flags</tt> rule described below.
</li>
<li>Translate build settings given in the global
<tt>gBUILD_PROPERTIES</tt> variable into something that can be used by
the toolset. The build system provides the <tt>flags</tt> rule to help
translate build properties into elements of global variables which are
later attached to targets so that they can affect the build actions. The
<tt>flags</tt> rule is used as follows:
<blockquote>
<pre>
flags <i>toolset variable condition</i> [: <i>value</i>...]
</pre>
</blockquote>The parameters are:
<ul>
<li><i>toolset</i> - the name of the toolset</li>
<li><i>variable</i> - the name of a global variable which can be used
to carry information to a command-line</li>
<li>
<i>condition</i> - one one or more elements in the following forms:
<ol>
<li>a property-set of the form:
<tt>&lt;<i>feature</i>&gt;<i>value</i></tt>[<tt>/&lt;<i>feature</i>&gt;
<i>value</i></tt>...]</li>
<li><tt>&lt;<i>feature</i>&gt;</tt></li>
</ol>
</li>
<li><i>values</i> - anything</li>
</ul>
<p>Semantics only affect targets built with the specified toolset, and
depend on the target's build configuration:</p>
<ol>
<li>if any specified property-set is a subset of the target's build
properties, the <i>values</i> specified in <tt>$(3)</tt> will be
appended once to <i>variable</i>.</li>
<li>The value of each specified feature that participates in the
target's build properties is appended to <i>variable</i>. In either
case, the variable will be set "on" the target so it may be used in
the build actions.</li>
</ol>
</li>
</ol>
<h4><a name="toolset_example" id="toolset_example">Example</a></h4>
<p>The description of the <tt>flags</tt> rule above is actually more
complicated than it sounds. For example, the following line might be used
to specify how optimization can be turned off for MSVC:</p>
<blockquote>
<pre>
flags msvc CFLAGS &lt;optimization&gt;off : /Od ;
</pre>
</blockquote>It says that the string <tt>/Od</tt> should be added to the
global <tt>CFLAGS</tt> variable whenever a build configuration includes the
property <tt>&lt;optimization&gt;off</tt>.
<p>Similarly, in the following example,</p>
<blockquote>
<pre>
flags msvc CFLAGS &lt;runtime-build&gt;release/&lt;runtime-link&gt;dynamic : /MD ;
</pre>
</blockquote>we add <tt>/MD</tt> to the CFLAGS variable when both of the
specified conditions are satisfied. We could grab all of the values of the
free feature <tt>&lt;include&gt;</tt> in the <tt>HDRS</tt> variable as
follows:
<blockquote>
<pre>
flags msvc HDRS &lt;include&gt; ;
</pre>
</blockquote>
<p>The use of these variables should be apparent from the declaration of
<tt>actions msvc-C++-action</tt> in the previous section.</p>
<h2><a name="internals" id="internals">Internals</a></h2>
<h3><a name="target_names" id="target_names">Target Names</a></h3>
<p>In addition to <a href="#user_targets">user targets</a>, which
correspond directly to the names the user writes in her subproject Jamfile,
several additional targets are generated, regardless of the directory from
which Jam was invoked:</p>
<ul>
<li>A <b>main target</b> has all the same dependencies as a user target
(i.e. building it updates all requested subvariants). Its name is the
same except for the addition of <tt>$(SOURCE_GRIST)</tt>, which
identifies the subproject. The identification looks like the names of the
path components from the project root to the subproject, separated by
exclamation points. Thus, if the project is rooted at <tt>foo</tt>, in
the subproject at <tt>foo/bar/baz</tt> the target <tt>my_target</tt> is
identified by <tt>&lt;bar!baz&gt;my_target</tt>.</li>
<li>A <b>subvariant target</b> has additional grist identifying its main
target and subvariant. This grist is joined to <tt>$(SOURCE_GRIST)</tt>
with the platform's directory separator. Thus, on UNIX, a subvariant
target of <tt>my_target</tt> above might be identified as
<tt>&lt;bar!baz/my_target/optimization-space/runtime-link-static&gt;my_source.o</tt>.
Note that the part of the grist following the first slash, known as the
<b>subvariant id</b>, also corresponds to a fragment of the subvariant
directory path where the corresponding target is generated. Most built
targets will be identified this way.</li>
</ul>
<h3><a name="internal_globals" id="internal_globals">Global
Variables</a></h3>
<p>This section describes some of the global variables used by the build
system. Please note that some parts of the system (particularly those in
<tt>allyourbase.jam</tt>) are heavily based on the Jambase file supplied
with Jam, and as such do not follow the conventions described below.</p>
<p>Global variables used in the build system fall into three
categories:</p>
<ul>
<li>Global variables intended to be set by the user on the command-line
or in the environment use <tt>ALL_UPPER_CASE</tt> names.</li>
<li>Internal global variables begin with a lower-case "g" and continue in
upper-case: <tt>gSOME_GLOBAL</tt></li>
<li>Global variables of the form:
<tt>gBASE_NAME(</tt><i>arguments</i><tt>)</tt>, where <i>arguments</i> is
a comma-separated argument list, are used internally to achieve a kind of
indirection by concatenating variable values:
<blockquote>
<pre>
ECHO $(gFUBAR($(x),$(y))) ;
</pre>
</blockquote>
</li>
</ul>
<p>Please note that the build system commonly takes advantage of <a href=
"../jam_src/Jam.html#bindingmods">Jam's Dynamic Scoping feature</a> (see
the <tt>local</tt> command in the "Flow of Control" section below the link
target) to temporarily "change" a global variable by declaring a
<tt>local</tt> of the same name.</p>
<p>Many of the variables that are used to configure how Boost.Build works
internally are listed <a href="variables.html">here</a> with brief
descriptions.</p>
<h3>Variables Associated with SubProject Identity</h3>
<ul>
<li><tt>SUBDIR_TOKENS</tt> - a list of the path elements relative to the
project root of the current subproject.</li>
<li><tt>SUBDIR</tt> - the path from the invocation directory to the
current subproject directory.</li>
</ul>
<h3>Grist Variables</h3>
<ul>
<li><tt>TARGET_GRIST</tt> takes the form
<tt><i>subproject!id</i>/target/toolset/variant/<i>subvariant-path</i></tt>.</li>
</ul>
<h2><a name="design_criteria" id="design_criteria">Design Criteria</a></h2>
<h3><a name="assumptions" id="assumptions">Assumptions</a></h3>
<p>The requirements are driven by several basic assumptions:</p>
<ul>
<li>There is no single Boost developer or test facility with access to or
knowledge of all the platforms and compilers Boost libraries are used
with.</li>
<li>Boost libraries are used across such a wide range of platforms and
compilers that almost no other assumptions can be made.</li>
</ul>
<h3><a name="requirements" id="requirements">Requirements</a></h3>
<p>This build system was designed to satisfy the following
requirements:</p>
<ul>
<li>A developer adding a new library or test program must only have to
add simple entries naming the source files to a text file, and not have
to know anything about platform specific files. The developer should not
have to supply header dependency information.</li>
<li>There should be a very high likelihood of builds succeeding on all
platforms if a build succeeds on any platform. In other words, a
developer must not be required to have access to many platforms or
compilers to ensure correct builds</li>
<li>A user or developer adding support for a new platform or compiler
should only have to add to a single file describing how to do the build
for that platform or compiler, and shouldn't have to identify the files
that will need to be built.</li>
<li>The build should rely only on tools native to the platform and
compiler, or supplied via the boost download.</li>
<li>The details of how the build is done for a particular platform or
compiler should be appropriate for that platform.</li>
<li>It should be possible to build multiple variants (e.g. debug/release)
of a single target.</li>
<li>It should be possible to build multiple variants of multiple targets
with multiple compilers from a single build command.</li>
<li>The build tools must be able to handle Boost growth issues such as
identified in Directory Structure proposals and discussion.</li>
<li>Support for dynamic and static linking should be included.</li>
<li>It should be relatively straightforward to add support for a new
compiler. In most cases, no modification of files used to describe
existing targets should be required.</li>
<li>Support for compiler- and variant-specific configuration for each
target</li>
<li>It should be possible to build targets into a directory unrelated to
the source directories (they may be read-only)</li>
</ul>
<h2><a name="footnotes" id="footnotes">Footnotes</a></h2><a name="one" id=
"one">[1]</a> Boost Jam is actually descended directly from <a href=
"http://freetype.sourceforge.net/jam/index.html">FTJam</a>, which was
itself a variant of <a href=
"http://www.perforce.com/jam/jam.html">Jam/MR</a>. It is hoped that crucial
features we rely on will eventually be incorporated back into the Jam/MR
release.
<p><a name="two" id="two">[2]</a> Note: right now, a dependency feature of
a main target makes <b>all</b> resulting built targets dependent, including
intermediate targets. That means that if an executable is dependent on an
external library, and that library changes, all the sources comprising the
executable will be recompiled as well. This behavior should probably be
fixed.</p>
<hr>
<p>Revised $Date$</p>
<p>Copyright &copy; Dave Abrahams 2001.</p>
<p><small>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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