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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE chapter PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
"http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
<chapter id="bbv2.overview">
<title>Overview</title>
<para>
This section will provide the information necessary to create your own
projects using Boost.Build. The information provided here is relatively
high-level, and <xref linkend="bbv2.reference"/> as well as the on-line
help system must be used to obtain low-level documentation (see <xref
linkend="bbv2.reference.init.options.help"/>).
</para>
<para>
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
<command>bjam</command> on the command line is as follows:
<orderedlist>
<listitem>
<para>
Boost.Jam tries to find Boost.Build and loads the top-level module.
The exact process is described in <xref linkend=
"bbv2.reference.init"/>
</para>
</listitem>
<listitem>
<para>
The top-level module loads user-defined configuration files,
<filename>user-config.jam</filename> and <filename>site-config.jam
</filename>, which define available toolsets.
</para>
</listitem>
<listitem>
<para>
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.
</para>
</listitem>
<listitem>
<para>
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.
</para>
</listitem>
</orderedlist>
</para>
<para>
So, to be able to successfully use Boost.Build, you need to know only four
things:
<itemizedlist>
<listitem>
<para>
<link linkend="bbv2.overview.configuration">How to configure
Boost.Build</link>
</para>
</listitem>
<listitem>
<para>
<link linkend="bbv2.overview.targets">How to declare targets in
Jamfiles</link>
</para>
</listitem>
<listitem>
<para>
<link linkend="bbv2.overview.build_process">How the build process
works</link>
</para>
</listitem>
<listitem>
<para>
Some Basics about the Boost.Jam language. See <xref linkend=
"bbv2.overview.jam_language"/>.
</para>
</listitem>
</itemizedlist>
</para>
<section id="bbv2.overview.concepts">
<title>Concepts</title>
<para>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.</para>
<para>
When using any flavour of make, you directly specify <firstterm>targets</firstterm>
and commands that are used to create them from other target. The below example
creates <filename>a.o</filename> from <filename>a.c</filename> using a hardcoded
compiler invocation command.
<programlisting>
a.o: a.c
g++ -o a.o -g a.c
</programlisting>
This is rather low-level description mechanism and it's hard to adjust commands, options,
and sets of created targets depending on the used compiler and operating system.
</para>
<para>
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:
<programlisting>
add_program ("a", "a.c")
</programlisting>
This is a function call that creates targets necessary to create executable file
from source file <filename>a.c</filename>. Depending on configured properties,
different commands line may be used. However, <code>add_program</code> is higher-level,
but rather thin level. All targets are created immediately when build description
is parsed, which makes it impossible to perform multi-variant builds. Often, change
in any build property requires complete reconfiguration of the build tree.
</para>
<para>
In order to support true multivariant builds, Boost.Build introduces the concept of
<indexterm> <primary>metatarget</primary> <secondary>definition</secondary></indexterm>
<indexterm> <primary>main target</primary> <see>metataget</see> </indexterm>
<firstterm>metatarget</firstterm>&mdash;object that is created when build description
is parsed and can be later called with specific build properties to generate
actual targets.
</para>
<para>
Consider an example:
<programlisting>
exe a : a.cpp ;
</programlisting>
When this declaration is parsed, Boost.Build creates a metatarget, but does not
yet decides what files must be created, or what commands must be used. After
all build files are parsed, Boost.Build considers properties requested on the
command line. Supposed you have invoked Boost.Build with:
<screen>
bjam toolset=gcc toolset=msvc
</screen>
In that case, the metatarget will be called twice, once with <code>toolset=gcc</code>
and once with <code>toolset=msvc</code>. Both invocations will produce concrete
targets, that will have different extensions and use different command lines.
</para>
<para>
Another key concept is
<indexterm><primary>property</primary><secondary>definition</secondary></indexterm>
<firstterm>build property</firstterm>. 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.
</para>
<para>
The final concept is <indexterm><primary>property</primary><secondary>propagation</secondary></indexterm>
<firstterm>property propagation</firstterm>. 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 <xref linkend="bbv2.overview.targets.requirements"/>).
Then, the dependency metatargets are called with modified properties and produce
concrete targets that are then used in build process. Of course, dependency metatargets
maybe in turn modify build properties and have dependencies of their own.
</para>
<para>For more in-depth treatment of the requirements and concepts, you may refer
to <ulink url="http://syrcose.ispras.ru/2009/files/04_paper.pdf">SYRCoSE 2009 Boost.Build article</ulink>.
</para>
</section>
<section id="bbv2.overview.jam_language">
<title>Boost.Jam Language</title>
<para>
This section will describe the basics of the Boost.Jam language&#x2014;
just enough for writing Jamfiles. For more information, please see the
<link linkend="bbv2.jam">Boost.Jam</link> documentation.
</para>
<para>
<link linkend="bbv2.jam">Boost.Jam</link> has an interpreted, procedural
language. On the lowest level, a <link linkend="bbv2.jam">Boost.Jam
</link> program consists of variables and <indexterm><primary>rule
</primary></indexterm> <firstterm>rules</firstterm> (Jam term for
function). They are grouped into modules&#x2014;there is one global
module and a number of named modules. Besides that, a <link linkend=
"bbv2.jam">Boost.Jam</link> program contains classes and class
instances.
</para>
<para>
Syntantically, a <link linkend="bbv2.jam">Boost.Jam</link> program
consists of two kind of elements&#x2014;keywords (which have a special
meaning to <link linkend="bbv2.jam">Boost.Jam</link>) and literals.
Consider this code:
<programlisting>
a = b ;
</programlisting>
which assigns the value <literal>b</literal> to the variable <literal>a
</literal>. Here, <literal>=</literal> and <literal>;</literal> are
keywords, while <literal>a</literal> and <literal>b</literal> are
literals.
<warning>
<para>
All syntax elements, even keywords, must be separated by spaces. For
example, omitting the space character before <literal>;</literal>
will lead to a syntax error.
</para>
</warning>
If you want to use a literal value that is the same as some keyword, the
value can be quoted:
<programlisting>
a = "=" ;
</programlisting>
</para>
<para>
All variables in <link linkend="bbv2.jam">Boost.Jam</link> have the same
type&#x2014;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>$(<replaceable>variable</replaceable>)</code> syntax. For example:
<programlisting>
a = $(b) $(c) ;
</programlisting>
</para>
<para>
Rules are defined by specifying the rule name, the parameter names, and
the allowed value list size for each parameter.
<programlisting>
rule <replaceable>example</replaceable>
(
<replaceable>parameter1</replaceable> :
<replaceable>parameter2 ?</replaceable> :
<replaceable>parameter3 +</replaceable> :
<replaceable>parameter4 *</replaceable>
)
{
# rule body
}
</programlisting>
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.
</para>
<para>
The overview of <link linkend="bbv2.jam">Boost.Jam</link> language
statements is given below:
<programlisting>
helper 1 : 2 : 3 ;
x = [ helper 1 : 2 : 3 ] ;
</programlisting>
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.
<programlisting>
if cond { statements } [ else { statements } ]
</programlisting>
This is a regular if-statement. The condition is composed of:
<itemizedlist>
<listitem>
<para>
Literals (true if at least one string is not empty)
</para>
</listitem>
<listitem>
<para>
Comparisons: <code>a <replaceable>operator</replaceable> b</code>
where <replaceable>operator</replaceable> is one of
<code>=</code>, <code>!=</code>, <code>&lt;</code>,
<code>&gt;</code>, <code>&lt;=</code> or <code>&gt;=</code>. The
comparison is done pairwise between each string in the left and
the right arguments.
</para>
</listitem>
<listitem>
<para>
Logical operations: <code>! a</code>, <code>a &amp;&amp; b</code>,
<code>a || b</code>
</para>
</listitem>
<listitem>
<para>
Grouping: <code>( cond )</code>
</para>
</listitem>
</itemizedlist>
<programlisting>
for var in list { statements }
</programlisting>
Executes statements for each element in list, setting the variable
<varname>var</varname> to the element value.
<programlisting>
while cond { statements }
</programlisting>
Repeatedly execute statements while cond remains true upon entry.
<programlisting>
return values ;
</programlisting>
This statement should be used only inside a rule and assigns
<code>values</code> to the return value of the rule.
<warning>
<para>
The <code>return</code> statement does not exit the rule. For
example:
<programlisting>
rule test ( )
{
if 1 = 1
{
return "reasonable" ;
}
return "strange" ;
}
</programlisting>
will return <literal>strange</literal>, not
<literal>reasonable</literal>.
</para>
</warning>
<programlisting>
import <replaceable>module</replaceable> ;
import <replaceable>module</replaceable> : <replaceable>rule</replaceable> ;
</programlisting>
The first form imports the specified bjam module. All rules from that
module are made available using the qualified name: <code><replaceable>
module</replaceable>.<replaceable>rule</replaceable></code>. The second
form imports the specified rules only, and they can be called using
unqualified names.
</para>
<para id="bbv2.overview.jam_language.actions">
Sometimes, you'd need to specify the actual command lines to be used
when creating targets. In jam language, you use named actions to do
this. For example:
<programlisting>
actions create-file-from-another
{
create-file-from-another $(&lt;) $(&gt;)
}
</programlisting>
This specifies a named action called <literal>
create-file-from-another</literal>. The text inside braces is the
command to invoke. The <literal>$(&lt;)</literal> variable will be
expanded to a list of generated files, and the <literal>$(&gt;)
</literal> variable will be expanded to a list of source files.
</para>
<para>
To flexibly adjust the command line, you can define a rule with the same
name as the action and taking three parameters -- targets, sources and
properties. For example:
<programlisting>
rule create-file-from-another ( targets * : sources * : properties * )
{
if &lt;variant&gt;debug in $(properties)
{
OPTIONS on $(targets) = --debug ;
}
}
actions create-file-from-another
{
create-file-from-another $(OPTIONS) $(&lt;) $(&gt;)
}
</programlisting>
In this example, the rule checks if certain build property is specified.
If so, it sets variable <varname>OPIONS</varname> that is then used
inside the action. Note that the variables set "on a target" will be
visible only inside actions building that target, not globally. Were
they set globally, using variable named <varname>OPTIONS</varname> in
two unrelated actions would be impossible.
</para>
<para>
More details can be found in Jam reference, <xref
linkend="jam.language.rules"/>.
</para>
</section>
<section id="bbv2.overview.configuration">
<title>Configuration</title>
<para>
On startup, Boost.Build searches and reads two configuration files:
<filename>site-config.jam</filename> and <filename>user-config.jam</filename>.
The first one is usually installed and maintained by system administrator, and
the second is for user to modify. You can edit the one in the top-level
directory of Boost.Build installation or create a copy in your home
directory and edit the copy. The following table explains where both files
are searched.
</para>
<table id="bbv2.reference.init.config">
<title>Search paths for configuration files</title>
<tgroup cols="3">
<thead>
<row>
<entry></entry>
<entry>site-config.jam</entry>
<entry>user-config.jam</entry>
</row>
</thead>
<tbody>
<row>
<entry>Linux</entry>
<entry>
<simpara><code>/etc</code></simpara>
<simpara><code>$HOME</code></simpara>
<simpara><code>$BOOST_BUILD_PATH</code></simpara>
</entry>
<entry>
<simpara><code>$HOME</code></simpara>
<simpara><code>$BOOST_BUILD_PATH</code></simpara>
</entry>
</row>
<row>
<entry>Windows</entry>
<entry>
<simpara><code>%SystemRoot%</code></simpara>
<simpara><code>%HOMEDRIVE%%HOMEPATH%</code></simpara>
<simpara><code>%HOME%</code></simpara>
<simpara><code>%BOOST_BUILD_PATH%</code></simpara>
</entry>
<entry>
<simpara><code>%HOMEDRIVE%%HOMEPATH%</code></simpara>
<simpara><code>%HOME%</code></simpara>
<simpara><code>%BOOST_BUILD_PATH%</code></simpara>
</entry>
</row>
</tbody>
</tgroup>
</table>
<tip>
<para>
You can use the <command>--debug-configuration</command> option to
find which configuration files are actually loaded.
</para>
</tip>
<para>
Usually, <filename>user-config.jam</filename> just defines available compilers
and other tools (see <xref linkend="bbv2.recipies.site-config"/> for more advanced
usage). A tool is configured using the following syntax:
</para>
<programlisting>
using <replaceable>tool-name</replaceable> : ... ;
</programlisting>
<para>
The <functionname>using</functionname> rule is given a name of tool, and
will make that tool available to Boost.Build. For example,
<programlisting>
using gcc ;
</programlisting> will make the <ulink url="http://gcc.gnu.org">GCC</ulink> compiler available.
</para>
<para>
All the supported tools are documented in <xref linkend="bbv2.reference.tools"/>,
including the specific options they take. Some general notes that apply to most
C++ compilers are below.
</para>
<para>
For all the C++ compiler toolsets Boost.Build supports
out-of-the-box, the list of parameters to
<functionname>using</functionname> is the same: <parameter
class="function">toolset-name</parameter>, <parameter
class="function">version</parameter>, <parameter
class="function">invocation-command</parameter>, and <parameter
class="function">options</parameter>.
</para>
<para>If you have a single compiler, and the compiler executable
<itemizedlist>
<listitem><para>has its &#x201C;usual name&#x201D; and is in the
<envar>PATH</envar>, or</para></listitem>
<listitem><para>was installed in a standard &#x201C;installation
directory&#x201D;, or</para></listitem>
<listitem><para>can be found using a global system like the Windows
registry.</para></listitem>
</itemizedlist>
it can be configured by simply:</para>
<programlisting>
using <replaceable>tool-name</replaceable> ;
</programlisting>
<!-- TODO: mention auto-configuration? -->
<para>If the compiler is installed in a custom directory, you should provide the
command that invokes the compiler, for example:</para>
<programlisting>
using gcc : : g++-3.2 ;
using msvc : : "Z:/Programs/Microsoft Visual Studio/vc98/bin/cl" ;
</programlisting>
<para>
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 compiler
executables for C and C++ are different, path to the C++ compiler
executable must be specified. The command can
be any command allowed by the operating system. For example:
<programlisting>
using msvc : : echo Compiling &#x26;&#x26; foo/bar/baz/cl ;
</programlisting>
will work.
</para>
<para>
To configure several versions of a toolset, simply invoke the
<functionname>using</functionname> rule multiple times:
<programlisting>
using gcc : 3.3 ;
using gcc : 3.4 : g++-3.4 ;
using gcc : 3.2 : g++-3.2 ;
</programlisting>
Note that in the first call to <functionname>using</functionname>, the
compiler found in the <envar>PATH</envar> will be used, and there is no
need to explicitly specify the command.
</para>
<!-- TODO: This is not actually relevant for gcc now, and we need to rethink this
<para>As shown above, both the <parameter
class="function">version</parameter> and <parameter
class="function">invocation-command</parameter> parameters are
optional, but there's an important restriction: if you configure
the same toolset more than once, you must pass the <parameter
class="function">version</parameter>
parameter every time. For example, the following is not allowed:
<programlisting>
using gcc ;
using gcc : 3.4 : g++-3.4 ;
</programlisting>
because the first <functionname>using</functionname> call does
not specify a <parameter class="function">version</parameter>.
</para> -->
<para>
Many of toolsets have an <parameter class="function">options</parameter>
parameter to fine-tune the configuration. All of
Boost.Build's standard compiler toolsets accept four options
<varname>cflags</varname>, <varname>cxxflags</varname>,
<varname>compileflags</varname> and <varname>linkflags</varname> as <parameter
class="function">options</parameter> specifying flags that will be
always passed to the corresponding tools. Values of the
<varname>cflags</varname> feature are passed directly to the C
compiler, values of the <varname>cxxflags</varname> feature are
passed directly to the C++ compiler, and values of the
<varname>compileflags</varname> feature are passed to both. For
example, to configure a <command>gcc</command> toolset so that it
always generates 64-bit code you could write:
<programlisting>
using gcc : 3.4 : : &lt;compileflags&gt;-m64 &lt;linkflags&gt;-m64 ;
</programlisting>
</para>
<warning>
<para>
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.
</para>
</warning>
</section>
<section id="bbv2.overview.invocation">
<title>Invocation</title>
<para>To invoke Boost.Build, type <command>bjam</command> on the command line. Three kinds
of command-line tokens are accepted, in any order:</para>
<variablelist>
<varlistentry>
<term>options</term>
<listitem><para>Options start with either dash, or two dashes. The standard options
are listed below, and each project may add additional options</para></listitem>
</varlistentry>
<varlistentry>
<term>properties</term>
<listitem><para>Properties specify details of what you want to build (e.g. debug
or release variant). Syntactically, all command line tokens with equal sign in them
are considered to specify properties. In the simplest form, property looks like
<command><replaceable>feature</replaceable>=<replaceable>value</replaceable></command>
</para></listitem>
</varlistentry>
<varlistentry>
<term>target</term>
<listitem><para>All tokens that are neither options nor properties specify
what targets to build. The available targets entirely depend on the project
you are building.</para></listitem>
</varlistentry>
</variablelist>
<section id="bbv2.overview.invocation.examples">
<title>Examples</title>
<para>To build all targets defined in Jamfile in the current directory with default properties, run:
<screen>
bjam
</screen>
</para>
<para>To build specific targets, specify them on the command line:
<screen>
bjam lib1 subproject//lib2
</screen>
</para>
<para>To request a certain value for some property, add <literal>
<replaceable>property</replaceable>=<replaceable>value</replaceable></literal> to the command line:
<screen>
bjam toolset=gcc variant=debug optimization=space
</screen>
</para>
</section>
<section id="bbv2.overview.invocation.options">
<title>Options</title>
<para>Boost.Build recognizes the following command line options.</para>
<variablelist>
<varlistentry id="bbv2.reference.init.options.help">
<term><option>--help</option></term>
<listitem>
<para>Invokes the online help system. This prints general
information on how to use the help system with additional
--help* options.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--clean</option></term>
<listitem>
<para>Cleans all targets in the current directory and
in any subprojects. Note that unlike the <literal>clean</literal>
target in make, you can use <literal>--clean</literal>
together with target names to clean specific targets.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--clean-all</option></term>
<listitem>
<para>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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--build-dir</option></term>
<listitem>
<para>Changes build directories for all project roots being built. When
this option is specified, all Jamroot files should declare project name.
The build directory for the project root will be computed by concatanating
the value of the <option>--build-dir</option> option, the project name
specified in Jamroot, and the build dir specified in Jamroot
(or <literal>bin</literal>, if none is specified).
</para>
<para>The option is primarily useful when building from read-only
media, when you can't modify Jamroot.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--version</option></term>
<listitem>
<para>Prints information on Boost.Build and Boost.Jam
versions.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-a</option></term>
<listitem>
<para>Causes all files to be rebuilt.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-n</option></term>
<listitem>
<para>Do no execute the commands, only print them.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-d+2</option></term>
<listitem>
<para>Show commands as they are executed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-d0</option></term>
<listitem>
<para>Supress all informational messages.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-q</option></term>
<listitem>
<para>Stop at first error, as opposed to continuing to build targets
that don't depend on the failed ones.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-j <replaceable>N</replaceable></option></term>
<listitem>
<para>Run up to <replaceable>N</replaceable> commands in parallel.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--debug-configuration</option></term>
<listitem>
<para>Produces debug information about loading of Boost.Build
and toolset files.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--debug-building</option></term>
<listitem>
<para>Prints what targets are being built and with what properties.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--debug-generators</option></term>
<listitem>
<para>Produces debug output from generator search process.
Useful for debugging custom generators.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--ignore-config</option></term>
<listitem>
<para>Do not load <literal>site-config.jam</literal> and
<literal>user-config.jam</literal> configuration files.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section id="bbv2.overview.invocation.properties">
<title>Properties</title>
<para>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
<command><replaceable>feature</replaceable>=<replaceable>value</replaceable></command>.
The complete list of features can be found in <xref linkend="bbv2.overview.builtins.features"/>.
The most common features are summarized below.</para>
<table>
<tgroup cols="3">
<thead>
<row>
<entry>Feature</entry>
<entry>Allowed values</entry>
<entry>Notes</entry>
</row>
</thead>
<tbody>
<row>
<entry>variant</entry>
<entry>debug,release</entry>
<entry></entry>
</row>
<row>
<entry>link</entry>
<entry>shared,static</entry>
<entry>Determines if Boost.Build creates shared or static libraries</entry>
</row>
<row>
<entry>threading</entry>
<entry>single,multi</entry>
<entry>Cause the produced binaries to be thread-safe. This requires proper support in the source code itself.</entry>
</row>
<row>
<entry>address-model</entry>
<entry>32,64</entry>
<entry>Explicitly request either 32-bit or 64-bit code generation. This typically
requires that your compiler is appropriately configured. Please refer to
<xref linkend="bbv2.reference.tools.compilers"/> and your compiler documentation
in case of problems.</entry>
</row>
<row>
<entry>toolset</entry>
<entry>(Depends on configuration)</entry>
<entry>The C++ compiler to use. See <xref linkend="bbv2.reference.tools.compilers"/> for a detailed list.</entry>
</row>
<row>
<entry>include</entry>
<entry>(Arbitrary string)</entry>
<entry>Additional include paths for C and C++ compilers.</entry>
</row>
<row>
<entry>define</entry>
<entry>(Arbitrary string)</entry>
<entry>Additional macro definitions for C and C++ compilers. The string should be either
<code>SYMBOL</code> or <code>SYMBOL=VALUE</code></entry>
</row>
<row>
<entry>cxxflags</entry>
<entry>(Arbitrary string)</entry>
<entry>Custom options to pass to the C++ compiler.</entry>
</row>
<row>
<entry>cflags</entry>
<entry>(Arbitrary string)</entry>
<entry>Custom options to pass to the C compiler.</entry>
</row>
<row>
<entry>linkflags</entry>
<entry>(Arbitrary string)</entry>
<entry>Custom options to pass to the C++ linker.</entry>
</row>
<row>
<entry>runtime-link</entry>
<entry>shared,static</entry>
<entry>Determines if shared or static version of C and C++ runtimes should be used.</entry>
</row>
</tbody>
</tgroup>
</table>
If you have more than one version of a given C++ toolset (e.g. configured in
<filename>user-config.jam</filename>, or autodetected, as happens with msvc), you can
request the specific version by passing
<code><replaceable>toolset</replaceable>-<replaceable>version</replaceable></code> as
the value of the <code>toolset</code> feature, for example <code>toolset=msvc-8.0</code>.
<para>
If a feature has a fixed set of values it can be specified more than
once on the command line. <!-- define 'base' and link to it -->
In which case, everything will be built several times --
once for each specified value of a feature. For example, if you use
</para>
<screen>
bjam link=static link=shared threading=single threading=multi
</screen>
<para>
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 commands, for example:
</para>
<screen>
bjam link=static,shared threading=single,multi
</screen>
<para>
The comma has special meaning only if the feature has a fixed set of values, so
</para>
<screen>
bjam include=static,shared
</screen>
<para>is not treated specially.</para>
</section>
<section id="bbv2.overview.invocation.targets">
<title>Targets</title>
<para>All command line elements that are neither options nor properties are the names of the
targets to build. See <xref linkend="bbv2.reference.ids"/>. If no target is specified,
the project in the current directory is built.</para>
</section>
</section>
<section id="bbv2.overview.targets">
<title>Declaring Targets</title>
<para id="bbv2.overview.targets.main">
A <firstterm>Main target</firstterm> 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 <xref linkend=
"bbv2.reference.rules"/>. The user can also declare
custom main target rules as shown in <xref
linkend="bbv2.extending.rules"/>.
</para>
<indexterm><primary>main target</primary><secondary>declaration
syntax</secondary></indexterm>
<para>Most main target rules in Boost.Build have the same common
signature:</para>
<!-- I think we maybe ought to be talking about a common
_signature_ here, having already explained Boost.Jam function
signatures at the beginning of this chapter. Then we could show
( main-target-name : sources * : requirements * : default-build * : usage-requirements * )
instead. More precise.
Also, I suggest replacing "default-build" by "default-properties" everywhere.
-->
<indexterm><primary>common signature</primary></indexterm>
<anchor id="bbv2.main-target-rule-syntax"/>
<programlisting>
rule <replaceable>rule-name</replaceable> (
main-target-name :
sources + :
requirements * :
default-build * :
usage-requirements * )
</programlisting>
<itemizedlist>
<listitem>
<simpara>
<parameter>main-target-name</parameter> 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
(&#x2018;<code>-</code>&#x2019;), and underscores
(&#x2018;<code>_</code>&#x2019;).
</simpara>
</listitem>
<listitem>
<simpara>
<parameter>sources</parameter> is the list of source files and other main
targets that must be combined.
</simpara>
</listitem>
<listitem>
<simpara>
<parameter>requirements</parameter> is the list of properties that must always
be present when this main target is built.
</simpara>
</listitem>
<listitem>
<simpara>
<parameter>default-build</parameter> 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.
</simpara>
</listitem>
<listitem>
<simpara>
<parameter>usage-requirements</parameter> is the list of properties that will be
propagated to all main targets that use this one, i.e. to all its
dependents.
</simpara>
</listitem>
</itemizedlist>
<para>
Some main target rules have a different list of parameters as explicitly
stated in their documentation.
</para>
<para>The actual requirements for a target are obtained by refining
requirements of the project where a target is declared with the
explicitly specified requirements. The same is true for
usage-requirements. More details can be found in
<xref linkend="bbv2.reference.variants.proprefine"/>
</para>
<section>
<title>Name</title>
<!-- perphaps we should use 'name-target-name' to closer
bind this description to the rule's signature. Here, and for
other parameters. -->
<para>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.
</para>
<para>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:</para>
<programlisting>
obj test.release : test.cpp : &lt;variant&gt;release ;
obj test.debug : test.cpp : &lt;variant&gt;debug ;
</programlisting>
<para>will generate two files named <filename>test.obj</filename> (in two different directories), not
two files named <filename>test.release.obj</filename> and <filename>test.debug.obj</filename>.
</para>
</section>
<section>
<title>Sources</title>
<para>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
<functionname>glob</functionname> rule. Here are two examples:</para>
<programlisting>
exe a : a.cpp ; # a.cpp is the only source file
exe b : [ glob *.cpp ] ; # all .cpp files in this directory are sources
</programlisting>
<para>
Unless you specify a file with an absolute path, the name is
considered relative to the source directory&#x200A;&#x2014;&#x200A;which is typically
the directory where the Jamfile is located, but can be changed as
described in <xref linkend=
"bbv2.overview.projects.attributes.projectrule"/>.
</para>
<para>
<!-- use "project-id" here? -->
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&#x2014;the part before the double
slash is first looked up as project name, and then as directory name.
For example:
</para>
<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 ;
</programlisting>
<para>
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 <ulink url=
"http://boost.org">C++ Boost</ulink> library, referring to it using
its absolute symbolic name. More information about target references
can be found in <xref linkend="bbv2.tutorial.libs"/> and <xref
linkend="bbv2.reference.ids"/>.
</para>
</section>
<section id="bbv2.overview.targets.requirements">
<title>Requirements</title>
<indexterm><primary>requirements</primary></indexterm>
<para>Requirements are the properties that should always be present when
building a target. Typically, they are includes and defines:
<programlisting>
exe hello : hello.cpp : &lt;include&gt;/opt/boost &lt;define&gt;MY_DEBUG ;
</programlisting>
There is a number of other features, listed in
<xref linkend="bbv2.overview.builtins.features"/>. 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
<programlisting>
lib util : util.cpp : &lt;link&gt;static ;
obj main : main.cpp : &lt;optimization&gt;off ;
</programlisting>
</para>
<para id="bbv2.overview.targets.requirements.conditional">Sometimes, particular relationships need to be maintained
among a target's build properties. This can be achieved with
<firstterm>conditional
requirements</firstterm>. For example, you might want to set
specific <code>#defines</code> when a library is built as shared,
or when a target's <code>release</code> variant is built in
release mode.
<programlisting>
lib network : network.cpp
: <emphasis role="bold">&lt;link&gt;shared:&lt;define&gt;NEWORK_LIB_SHARED</emphasis>
&lt;variant&gt;release:&lt;define&gt;EXTRA_FAST
;
</programlisting>
In the example above, whenever <filename>network</filename> is
built with <code>&lt;link&gt;shared</code>,
<code>&lt;define&gt;NEWORK_LIB_SHARED</code> will be in its
properties, too.
</para>
<para>You can use several properties in the condition, for example:
<programlisting>
lib network : network.cpp
: &lt;toolset&gt;gcc,&lt;optimization&gt;speed:&lt;define&gt;USE_INLINE_ASSEMBLER
;
</programlisting>
</para>
<para id="bbv2.overview.targets.requirements.indirect">
A more powerful variant of conditional requirements
is <firstterm>indirect conditional requirements</firstterm>.
You can provide a rule that will be called with the current build properties and can compute additional properties
to be added. For example:
<programlisting>
lib network : network.cpp
: &lt;conditional&gt;@my-rule
;
rule my-rule ( properties * )
{
local result ;
if &lt;toolset&gt;gcc &lt;optimization&gt;speed in $(properties)
{
result += &lt;define&gt;USE_INLINE_ASSEMBLER ;
}
return $(result) ;
}
</programlisting>
This example is equivalent to the previous one, but for complex cases, indirect conditional
requirements can be easier to write and understand.
</para>
<para>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 specific project's requirement
using the syntax by adding a minus sign before a property, for example:
<programlisting>
exe main : main.cpp : <emphasis role="bold">-&lt;define&gt;UNNECESSARY_DEFINE</emphasis> ;
</programlisting>
This syntax is the only way to ignore free properties from a parent,
such as defines. It can be also useful for ordinary properties. Consider
this example:
<programlisting>
project test : requirements &lt;threading&gt;multi ;
exe test1 : test1.cpp ;
exe test2 : test2.cpp : &lt;threading&gt;single ;
exe test3 : test3.cpp : -&lt;threading&gt;multi ;
</programlisting>
Here, <code>test1</code> inherits project requirements and will always
be built in multi-threaded mode. The <code>test2</code> target
<emphasis>overrides</emphasis> project's requirements and will
always be built in single-threaded mode. In contrast, the
<code>test3</code> target <emphasis>removes</emphasis> a property
from project requirements and will be built either in single-threaded or
multi-threaded mode depending on which variant is requested by the
user.</para>
<para>Note that the removal of requirements is completely textual:
you need to specify exactly the same property to remove it.</para>
</section>
<section>
<title>Default Build</title>
<para>The <varname>default-build</varname> 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:
<programlisting>
exe hello : hello.cpp : : &lt;threading&gt;multi ;
</programlisting>
would build a multi-threaded target unless the user
explicitly requests a single-threaded version. The difference between
requirements and default-build is that requirements cannot be
overridden in any way.
</para>
</section>
<section>
<title>Additional Information</title>
<para>
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 <firstterm>target
alternatives</firstterm>:
<programlisting>
lib demangler : dummy_demangler.cpp ; # alternative 1
lib demangler : demangler_gcc.cpp : &lt;toolset&gt;gcc ; # alternative 2
lib demangler : demangler_msvc.cpp : &lt;toolset&gt;msvc ; # alternative 3
</programlisting>
In the example above, when built with <literal>gcc</literal>
or <literal>msvc</literal>, <filename>demangler</filename>
will use a source file specific to the toolset. Otherwise, it
will use a generic source file,
<filename>dummy_demangler.cpp</filename>.
</para>
<para>It is possible to declare a target inline, i.e. the "sources"
parameter may include calls to other main rules. For example:</para>
<programlisting>
exe hello : hello.cpp
[ obj helpers : helpers.cpp : &lt;optimization&gt;off ] ;</programlisting>
<para>
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>bjam hello..helpers</code>.
</para>
<para>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
<functionname>explicit</functionname> rule:
<programlisting>
explicit install_programs ;</programlisting>
</para>
</section>
</section>
<section id="bbv2.overview.projects">
<title>Projects</title>
<para>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.
</para>
<para>Projects are named using the
<functionname>project</functionname> rule, which has the
following syntax:
<programlisting>
project <replaceable>id</replaceable> : <replaceable>attributes</replaceable> ;
</programlisting>
Here, <replaceable>attributes</replaceable> 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:
<programlisting>
project tennis
: requirements &lt;threading&gt;multi
: default-build release
;
</programlisting>
</para>
<para>The possible attributes are listed below.</para>
<para><emphasis>Project id</emphasis> 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". <link linkend=
"bbv2.reference.ids">Target references</link> make use of project ids to
specify a target.</para>
<!--
This is actually spelled "project-id," isn't it? You
have to fix all of these and use a code font. Also below
in the table.
-->
<para><emphasis>Source location</emphasis> specifies the directory where sources
for the project are located.</para>
<para><emphasis>Project requirements</emphasis> are requirements that apply to
all the targets in the projects as well as all subprojects.</para>
<para><emphasis>Default build</emphasis> is the build request that should be
used when no build request is specified explicitly.</para>
<!--
This contradicts your earlier description of default
build and I believe it is incorrect. Specifying a build
request does not neccessarily render default build
ineffective, because it may cover different features.
This description is repeated too many times in the
documentation; you almost *had* to get it wrong once.
-->
<para id="bbv2.overview.projects.attributes.projectrule">
The default values for those attributes are
given in the table below.
<table>
<title/>
<tgroup cols="4">
<thead>
<row>
<entry>Attribute</entry>
<entry>Name</entry>
<entry>Default value</entry>
<entry>Handling by the <functionname>project</functionname>
rule</entry>
</row>
</thead>
<tbody>
<row>
<entry>Project id</entry>
<entry>none</entry>
<entry>none</entry>
<entry>Assigned from the first parameter of the 'project' rule.
It is assumed to denote absolute project id.</entry>
</row>
<row>
<entry>Source location</entry>
<entry><literal>source-location</literal></entry>
<entry>The location of jamfile for the project</entry>
<entry>Sets to the passed value</entry>
</row>
<row>
<entry>Requirements</entry>
<entry><literal>requirements</literal></entry>
<entry>The parent's requirements</entry>
<entry>The parent's requirements are refined with the passed
requirement and the result is used as the project
requirements.</entry>
</row>
<row>
<entry>Default build</entry>
<entry><literal>default-build</literal></entry>
<entry>none</entry>
<entry>Sets to the passed value</entry>
</row>
<row>
<entry>Build directory</entry>
<entry><literal>build-dir</literal></entry>
<entry>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.
</entry>
<entry>Sets to the passed value, interpreted as relative to the
project's location.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>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
<xref linkend="bbv2.reference.rules"/>.
</para>
<para>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 <filename>Jamroot</filename> rather than
<filename>Jamfile</filename>. When loading a project,
Boost.Build looks for either <filename>Jamroot</filename> or
<code>Jamfile</code>. They are handled identically, except
that if the file is called <filename>Jamroot</filename>, the
search for a parent project is not performed.
</para>
<para>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>use-project</code> or a target reference,
no specific order should be assumed.
</para>
<note>
<para>Giving the root project the special name
&#x201C;<filename>Jamroot</filename>&#x201D; ensures that
Boost.Build won't misinterpret a directory above it as the
project root just because the directory contains a Jamfile.
<!-- The logic of the previous reasoning didn't hang together -->
</para>
</note>
<!-- All this redundancy with the tutorial is bad. The tutorial
should just be made into the introductory sections of this
document, which should be called the "User Guide." It's
perfectly appropriate to start a user guide with that kind
of material. -->
</section>
<section id="bbv2.overview.build_process">
<title>The Build Process</title>
<para>When you've described your targets, you want Boost.Build to run the
right tools and create the needed targets.
<!-- That sentence is awkward and doesn't add much. -->
This section will describe
two things: how you specify what to build, and how the main targets are
actually constructed.
</para>
<para>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.”
<!-- Do we need a new word? We already have “main target.” If
you're going to introduce “metatarget” you should at least
tie it together with the main target concept. It's too
strange to have been saying “main target” all along and now
suddenly start saying “what you declare in a jamfile” -->
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.
</para>
<tip>
<para>
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.
</para>
</tip>
<section id="bbv2.overview.build_request">
<title>Build Request</title>
<para>
The command line specifies which targets to build and with which
properties. For example:
<programlisting>
bjam app1 lib1//lib1 toolset=gcc variant=debug optimization=full
</programlisting>
would build two targets, "app1" and "lib1//lib1" with the specified
properties. You can refer to any targets, using
<link linkend="bbv2.reference.ids">target id</link> 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:
<programlisting>
bjam app1 lib1//lib1 gcc debug optimization=full
</programlisting>
The complete syntax, which has some additional shortcuts, is
described in <xref linkend="bbv2.overview.invocation"/>.
</para>
</section>
<section><title>Building a main target</title>
<para>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 <xref
linkend="bbv2.reference.buildprocess"/>.
<orderedlist>
<listitem><para>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.</para>
<!--
Added to what? Don't say “the build request!” The
request is what was requested; if its meaning changes
the reader will be confused.
-->
</listitem>
<listitem><para>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.
</para></listitem>
<listitem><para>Determining "common" properties.
<!-- It would be nice to have a better name for this. But
even more importantly, unless you say something about
the reason for choosing whatever term you use, the
reader is going to wonder what it means. -->
The build request
is <link linkend="bbv2.reference.variants.proprefine">refined</link>
with target's requirements.
<!-- It's good that you have the links here and below,
but I'm concerned that it doesn't communicate well
in print and there's not enough information for the
print reader. Maybe we need separate XSL for PDF
printing that generates a readable footnote. -->
The conditional properties in
requirements are handled as well. Finally, default values of
features are added.
</para></listitem>
<listitem><para>Building targets referred by the sources list and
dependency properties. The list of sources and the properties
can refer to other target using <link
linkend="bbv2.reference.ids">target references</link>. For each
reference, we take all <link
linkend="bbv2.reference.features.attributes.propagated">propagated</link>
properties, refine them by explicit properties specified in the
target reference, and pass the resulting properties as build
request to the other target.
</para></listitem>
<listitem><para>Adding the usage requirements produced when building
dependencies to the "common" properties. When dependencies are
built in the previous step, they return
<!-- don't assume reader has a mental model for BB internals! -->
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.
</para></listitem>
<listitem><para>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.
</para></listitem>
<listitem><para>Computing the usage requirements to be returned. The
conditional properties in usage requirements are expanded
<!-- what does "expanded" mean? -->
and the result is returned.</para></listitem>
</orderedlist>
</para>
</section>
<section><title>Building a Project</title>
<para>Often, a user builds a complete project, not just one main
target. In fact, invoking <command>bjam</command> without
arguments
<!-- do you know the difference between parameters and
arguments? I only learned this year -->
builds the project defined in the current
directory.</para>
<para>When a project is built, the build request is passed without
modification to all main targets in that project.
<!-- What does it mean to pass a build request to a target?
-->
It's is possible to
prevent implicit building of a target in a project with the
<code>explicit</code> rule:
<programlisting>
explicit hello_test ;
</programlisting>
would cause the <code>hello_test</code> target to be built only if
explicitly requested by the user or by some other target.
</para>
<para>The Jamfile for a project can include a number of
<code>build-project</code> rule calls that specify additional projects to
be built.
</para>
</section>
</section>
</chapter>
<!--
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sgml-indent-data: t
sgml-parent-document: ("userman.xml" "chapter")
sgml-set-face: t
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