[[bbv2.reference]]
= Reference

[[bbv2.reference.general]]
== General information

[[bbv2.reference.init]]
=== Initialization

Immediately upon starting, the Boost.Build engine (*`b2`*) loads the Jam
code that implements the build system. To do this, it searches for a
file called `boost-build.jam`, first in the invocation directory, then
in its parent and so forth up to the filesystem root, and finally in the
directories specified by the environment variable BOOST_BUILD_PATH. When
found, the file is interpreted, and should specify the build system
location by calling the boost-build rule:

[source]
----
rule boost-build ( location ? )
----

If location is a relative path, it is treated as relative to the
directory of `boost-build.jam`. The directory specified by that location
and the directories in BOOST_BUILD_PATH are then searched for a file
called `bootstrap.jam`, which is expected to bootstrap the build system.
This arrangement allows the build system to work without any
command-line or environment variable settings. For example, if the build
system files were located in a directory "build-system/" at your project
root, you might place a `boost-build.jam` at the project root
containing:

[source]
----
boost-build build-system ;
----

In this case, running *`b2`* anywhere in the project tree will
automatically find the build system.

The default `bootstrap.jam`, after loading some standard definitions,
loads both `site-config.jam` and `user-config.jam`.

[[bbv2.reference.rules]]
== Builtin rules

This section contains the list of all rules that can be used in
Jamfile — both rules that define new targets and auxiliary rules.

[[bbv2.reference.rules.exe]]`exe`::
Creates an executable file. See
link:#bbv2.tasks.programs[the section called “Programs”].

[[bbv2.reference.rules.lib]]`lib`::
Creates an library file. See
link:#bbv2.tasks.libraries[the section called “Libraries”].

[[bbv2.reference.rules.install]]`install`::
Installs built targets and other files. See
link:#bbv2.tasks.installing[the section called “Installing”].

[[bbv2.reference.rules.alias]]`alias`::
Creates an alias for other targets. See
link:#bbv2.tasks.alias[the section called “Alias”].

[[bbv2.reference.rules.unit-test]]`unit-test`::
Creates an executable that will be automatically run. See
link:#bbv2.builtins.testing[the section called “Testing”].

[[bbv2.reference.rules.test]]`compile`; `compile-fail`; `link`; `link-fail`; `run`; `run-fail`::
Specialized rules for testing. See
link:#bbv2.builtins.testing[the section called “Testing”].

[[bbv2.reference.rules.check-target-builds]]`check-target-builds`::
The `check-target-builds` allows you to conditionally use different
properties depending on whether some metatarget builds, or not. This
is similar to functionality of configure script in `autotools` projects.
The function signature is:
+
----
rule check-target-builds ( target message ? : true-properties * : false-properties * )
----
+
This function can only be used when passing requirements or usage
requirements to a metatarget rule. For example, to make an application
link to a library if it's available, one has use the following:
+
----
exe app : app.cpp : [ check-target-builds has_foo "System has foo" : <library>foo : <define>FOO_MISSING=1 ] ;
----
+
For another example, the alias rule can be used to consolidate
configuration choices and make them available to other metatargets,
like so:
+
----
alias foobar : : : : [ check-target-builds has_foo "System has foo" : <library>foo : <library>bar ] ;
----

[[bbv2.reference.rules.obj]]`obj`::
Creates an object file. Useful when a single source file must be
compiled with special properties.

[[bbv2.reference.rules.preprocessed]]`preprocessed`::
Creates an preprocessed source file. The arguments follow the
link:#bbv2.main-target-rule-syntax[common syntax].

[[bbv2.reference.rules.glob]]`glob`::
The `glob` rule takes a list shell pattern and returns the list of
files in the project's source directory that match the pattern. For
example:
+
----
lib tools : [ glob *.cpp ] ;
----
+
It is possible to also pass a second argument—the list of exclude
patterns. The result will then include the list of files matching any
of include patterns, and not matching any of the exclude patterns. For
example:
+
----
lib tools : [ glob *.cpp : file_to_exclude.cpp bad*.cpp ] ;
----

[[bbv2.reference.glob-tree]]`glob-tree`::
The `glob-tree` is similar to the `glob` except that it operates
recursively from the directory of the containing Jamfile. For example:
+
----
ECHO [ glob-tree *.cpp : .svn ] ;
----
+
will print the names of all {CPP} files in your project. The `.svn`
exclude pattern prevents the `glob-tree` rule from entering
administrative directories of the Subversion version control system.

[[bbv2.reference.rules.project]]`project`::
Declares project id and attributes, including project requirements.
See link:#bbv2.overview.projects[the section called “Projects”].

[[bbv2.reference.rules.use-project]]`use-project`::
Assigns a symbolic project ID to a project at a given path. This rule
must be better documented!

[[bbv2.reference.rules.explicit]]`explicit`::
The `explicit` rule takes a single parameter--a list of target names.
The named targets will be marked explicit, and will be built only if
they are explicitly requested on the command line, or if their
dependents are built. Compare this to ordinary targets, that are built
implicitly when their containing project is built.

[[bbv2.reference.rules.always]]`always`::
The `always` function takes a single parameter—a list of metatarget
names. The top-level targets produced by the named metatargets will be
always considered out of date. Consider this example:
+
----
exe hello : hello.cpp ;
exe bye : bye.cpp ;
always hello ;
----
+
If a build of `hello` is requested, then the binary will always be
relinked. The object files will not be recompiled, though. Note that
if a build of `hello` is not requested, for example you specify just
`bye` on the command line, `hello` will not be relinked.

[[bbv2.reference.rules.constant]]`constant`::
Sets project-wide constant. Takes two parameters: variable name and a
value and makes the specified variable name accessible in this Jamfile
and any child Jamfiles. For example:
+
----
constant VERSION : 1.34.0 ;
----

[[bbv2.reference.rules.path-constant]]`path-constant`::
Same as `constant` except that the value is treated as path relative
to Jamfile location. For example, if `b2` is invoked in the current
directory, and Jamfile in `helper` subdirectory has:
+
----
path-constant DATA : data/a.txt ;
----
+
then the variable `DATA` will be set to `helper/data/a.txt`, and if
*`b2`* is invoked from the `helper` directory, then the variable `DATA`
will be set to `data/a.txt`.

[[bbv2.reference.rules.build-project]]`build-project`::
Cause some other project to be built. This rule takes a single
parameter—a directory name relative to the containing Jamfile. When
the containing Jamfile is built, the project located at that directory
will be built as well. At the moment, the parameter to this rule
should be a directory name. Project ID or general target references
are not allowed.

[[bbv2.reference.rules.test-suite]]`test-suite`::
This rule is deprecated and equivalent to `alias`.

[[bbv2.overview.builtins.features]]
== Builtin features

This section documents the features that are built-in into Boost.Build.
For features with a fixed set of values, that set is provided, with the
default value listed first.

[[bbv2.builtin.features.variant]]`variant`::
*Allowed values:* `debug`, `release`, `profile`.
+
A feature combining several low-level features, making it easy to
request common build configurations.
+
The value `debug` expands to
+
----
<optimization>off <debug-symbols>on <inlining>off <runtime-debugging>on
----
+
The value `release` expands to
+
----
<optimization>speed <debug-symbols>off <inlining>full <runtime-debugging>off
----
+
The value `profile` expands to the same as `release`, plus:
+
----
<profiling>on <debug-symbols>on
----
+
Users can define their own build variants using the `variant` rule
from the `common` module.
+
NOTE: Runtime debugging is on in debug builds to suit the expectations of
people used to various IDEs.

[[bbv2.builtin.features.link]]`link`::
*Allowed values:* `shared`, `static`
+
A feature controlling how libraries are built.

[[bbv2.builtin.features.runtime-link]]`runtime-link`::
*Allowed values:* `shared`, `static`
+
Controls if a static or shared C/{CPP} runtime should be used. There are
some restrictions how this feature can be used, for example on some
compilers an application using static runtime should not use shared
libraries at all, and on some compilers, mixing static and shared
runtime requires extreme care. Check your compiler documentation for
more details.

[[bbv2.builtin.features.threading]]`threading`::
*Allowed values:* `single`, `multi`
+
Controls if the project should be built in multi-threaded mode. This
feature does not necessary change code generation in the compiler, but
it causes the compiler to link to additional or different runtime
libraries, and define additional preprocessor symbols (for example,
`_MT` on Windows and `_REENTRANT` on Linux). How those symbols affect
the compiled code depends on the code itself.

[[bbv2.builtin.features.source]]`source`::
The `<source>X` feature has the same effect on building a target as
putting X in the list of sources. It is useful when you want to add
the same source to all targets in the project (you can put <source> in
requirements) or to conditionally include a source (using conditional
requirements, see
link:#bbv2.tutorial.conditions[the section called “Conditions and alternatives”]).
See also the `<library>` feature.

[[bbv2.builtin.features.library]]`library`::
This feature is almost equivalent to the `<source>` feature, except
that it takes effect only for linking. When you want to link all
targets in a Jamfile to certain library, the `<library>` feature is
preferred over `<source>X`--the latter will add the library to all
targets, even those that have nothing to do with libraries.

[[bbv2.builtin.features.dependency]]`dependency`::
Introduces a dependency on the target named by the value of this
feature (so it will be brought up-to-date whenever the target being
declared is). The dependency is not used in any other way.

[[bbv2.builtin.features.implicit-dependency]]`implicit-dependency`::
Indicates that the target named by the value of this feature may
produce files that are included by the sources of the target being
declared. See
link:#bbv2.reference.generated_headers[the section called “Generated headers”]
for more information.

[[bbv2.builtin.features.use]]`use`::
Introduces a dependency on the target named by the value of this
feature (so it will be brought up-to-date whenever the target being
declared is), and adds its usage requirements to the build properties
of the target being declared. The dependency is not used in any other
way. The primary use case is when you want the usage requirements
(such as `#include` paths) of some library to be applied, but do not
want to link to it.

[[bbv2.builtin.features.dll-path]]`dll-path`::
Specify an additional directory where the system should look for
shared libraries when the executable or shared library is run. This
feature only affects Unix compilers. Please see
link:#bbv2.faq.dll-path[the FAQ: “Why are the dll-path and hardcode-dll-paths properties useful? ”]
in link:#bbv2.faq[Frequently Asked Questions] for details.

[[bbv2.builtin.features.hardcode-dll-paths]]`hardcode-dll-paths`::
*Allowed values:* `true`, `false`.
+
Controls automatic generation of dll-path properties.
+
This property is specific to Unix systems. If an executable is built with
`<hardcode-dll-paths>true`, the generated binary will contain the list of all
the paths to the used shared libraries. As the result, the executable can be
run without changing system paths to shared libraries or installing the
libraries to system paths. This is very convenient during development.
Please see the link:#bbv2.faq.dll-path[FAQ entry] for details. Note
that on Mac OSX, the paths are unconditionally hardcoded by the
linker, and it is not possible to disable that behavior

[[bbv2.builtin.features.flags]]`cflags`; `cxxflags`; `linkflags`::
The value of those features is passed without modification to the
corresponding tools. For `cflags` that is both the C and {CPP}
compilers, for `cxxflags` that is the {CPP} compiler, and for
`linkflags` that is the linker. The features are handy when you are
trying to do something special that cannot be achieved by a
higher-level feature in Boost.Build.

[[bbv2.builtin.features.include]]`include`::
Specifies an additional include path that is to be passed to C and {CPP}
compilers.

[[bbv2.builtin.features.define]]`define`::
Specifies an preprocessor symbol that should be defined on the command
line. You may either specify just the symbol, which will be defined
without any value, or both the symbol and the value, separated by
equal sign.

[[bbv2.builtin.features.warnings]]`warnings`::
The `<warnings>` feature controls the warning level of compilers. It
has the following values:
+
* `off` - disables all warnings.
* `on` - enables default warning level for the tool.
* `all` - enables all warnings.
+
Default value is `all`.

[[bbv2.builtin.features.warnings-as-errors]]`warnings-as-errors`::
The `<warnings-as-errors>` makes it possible to treat warnings as
errors and abort compilation on a warning. The value `on` enables this
behavior. The default value is `off`.

[[bbv2.builtin.features.build]]`build`::
*Allowed values:* `no`
+
The `build` feature is used to conditionally disable build of a
target. If `<build>no` is in properties when building a target, build
of that target is skipped. Combined with conditional requirements this
allows you to skip building some target in configurations where the
build is known to fail.

[[bbv2.builtin.features.tag]]`tag`::
The `tag` feature is used to customize the name of the generated
files. The value should have the form:
+
----
@rulename
----
+
where _rulename_ should be a name of a rule with the following
signature:
+
----
rule tag ( name : type ? : property-set )
----
+
The rule will be called for each target with the default name computed
by Boost.Build, the type of the target, and property set. The rule can
either return a string that must be used as the name of the target, or
an empty string, in which case the default name will be used.
+
Most typical use of the `tag` feature is to encode build properties,
or library version in library target names. You should take care to
return non-empty string from the tag rule only for types you care
about -- otherwise, you might end up modifying names of object files,
generated header file and other targets for which changing names does
not make sense.

[[bbv2.builtin.features.debug-symbols]]`debug-symbols`::
*Allowed values:* `on`, `off`.
+
The `debug-symbols` feature specifies if produced object files,
executables, and libraries should include debug information.
Typically, the value of this feature is implicitly set by the
`variant` feature, but it can be explicitly specified by the user. The
most common usage is to build release variant with debugging
information.

[[bbv2.builtin.features.runtime-debugging]]`runtime-debugging`::
*Allowed values:* `on`, `off`.
+
The `runtime-debugging` feature specifies whether produced object
files, executables, and libraries should include behavior useful only
for debugging, such as asserts. Typically, the value of this feature
is implicitly set by the `variant` feature, but it can be explicitly
specified by the user. The most common usage is to build release
variant with debugging output.

[[bbv2.builtin.features.target-os]]`target-os`::
The operating system for which the code is to be generated. The
compiler you used should be the compiler for that operating system.
This option causes Boost.Build to use naming conventions suitable for
that operating system, and adjust build process accordingly. For
example, with gcc, it controls if import libraries are produced for
shared libraries or not.
+
The complete list of possible values for this feature is: `aix`,
`appletv`, `bsd`, `cygwin`, `darwin`, `freebsd`, `hpux`, `iphone`, `linux`, `netbsd`,
`openbsd`, `osf`, `qnx`, `qnxnto`, `sgi`, `solaris`, `unix`, `unixware`, `windows`.
+
See link:#bbv2.tasks.crosscompile[the section called “Cross-compilation”]
for details of cross-compilation.

[[bbv2.builtin.features.architecture]]`architecture`::
*Allowed values:* `x86`, `ia64`, `sparc`, `power`, `mips1`, `mips2`,
`mips3`, `mips4`, `mips32`, `mips32r2`, `mips64`, `parisc`, `arm`,
`combined`, `combined-x86-power`.
+
The `architecture` features specifies the general processor family to
generate code for.

[[bbv2.builtin.features.instruction-set]]`instruction-set`::
*Allowed values:* depends on the used toolset.
+
The `instruction-set` specifies for which specific instruction set the
code should be generated. The code in general might not run on
processors with older/different instruction sets.
+
While Boost.Build allows a large set of possible values for this
features, whether a given value works depends on which compiler you
use. Please see
link:#bbv2.reference.tools.compilers[the section called “C++ Compilers”]
for details.

[[bbv2.builtin.features.address-model]]`address-model`::
*Allowed values:* `32`, `64`.
+
The `address-model` specifies if 32-bit or 64-bit code should be
generated by the compiler. Whether this feature works depends on the
used compiler, its version, how the compiler is configured, and the
values of the `architecture` `instruction-set` features. Please see
link:#bbv2.reference.tools.compilers[the section called “C++ Compilers”]
for details.

[[bbv2.builtin.features.cpp-template-depth]]`c++-template-depth`::
*Allowed values:* Any positive integer.
+
This feature allows configuring a {CPP} compiler with the maximal
template instantiation depth parameter. Specific toolsets may or may
not provide support for this feature depending on whether their
compilers provide a corresponding command-line option.
+
NOTE: Due to some internal details in the current Boost.Build
implementation it is not possible to have features whose valid values
are all positive integer. As a workaround a large set of allowed
values has been defined for this feature and, if a different one is
needed, user can easily add it by calling the feature.extend rule.

[[bbv2.builtin.features.embed-manifest]]`embed-manifest`::
*Allowed values:* `on`, `off`.
+
This feature is specific to the msvc toolset (see
link:#bbv2.reference.tools.compiler.msvc[the section called “Microsoft Visual {CPP}”]),
and controls whether the manifest files should be embedded inside executables
and shared libraries, or placed alongside them. This feature corresponds
to the IDE option found in the project settings dialog, under
Configuration Properties -> Manifest Tool -> Input and Output -> Embed
manifest.

[[bbv2.builtin.features.embed-manifest-file]]`embed-manifest-file`::
This feature is specific to the msvc toolset (see
link:#bbv2.reference.tools.compiler.msvc[the section called “Microsoft Visual {CPP}”]),
and controls which manifest files should be embedded inside executables and
shared libraries. This feature corresponds to the IDE option found in the
project settings dialog, under Configuration Properties -> Manifest
Tool -> Input and Output -> Additional Manifest Files.

[[bbv2.builtin.features.relevant]]`relevant`::
*Allowed values:* the name of any feature.
+
This feature is used to indicate which other features are relevant for a
given target. It is usually not necessary to manage it explicitly, as
Boost.Build can deduce it in most cases. Features which are not relevant
will not affect target paths, and will not cause conflicts.
+
* A feature will be considered relevant if any of the following are true
+
** It is referenced by `toolset.flags` or `toolset.uses-features`
** It is used by the requirements of a generator
** It is a sub-feature of a relevant feature
** It has a sub-feature which is relevant
** It is a composite feature, and any composed feature is relevant
** It affects target alternative selection for a main target
** It is a propagated feature and is relevant for any dependency
** It is relevant for any dependency created by the same main target
** It is used in the condition of a conditional property and the corresponding
  value is relevant
** It is explicitly named as relevant
+
* Relevant features cannot be automatically deduced in the following cases:
+
** Indirect conditionals. Solution: return properties of the form
`<relevant>result-feature:<relevant>condition-feature`
+
NOTE: This isn't really a conditional, although for most purposes it
functions like one. In particular, it does not support multiple
comma-separated elements in the condition, and it does work correctly even
in contexts where conditional properties are not allowed
** Action rules that read properties. Solution: add toolset.uses-features to
tell Boost.Build that the feature is actually used.
** Generators and targets that manipulate property-sets directly. Solution: set <relevant> manually.

[[bbv2.builtin.features.visibility]]`visibility`::
*Allowed values:* `global`, `protected`, `hidden`.
+
This feature is used to specify the default symbol visibility in compiled
binaries. Not all values are supported on all platforms and on some
platforms (for example, Windows) symbol visibility is not supported at all.
+
The supported values have the following meaning:
+
* `global` - a.k.a. "default" in gcc documentation. Global symbols are considered
  public, they are exported from shared libraries and can be redefined by another
  shared library or executable.
* `protected` - a.k.a. "symbolic". Protected symbols are exported from shared
  libraries but cannot be redefined by another shared library or executable.
  This mode is not supported on some platforms, for example OS X.
* `hidden` - Hidden symbols are not exported from shared libraries and cannot
  be redefined by a different shared library or executable loaded in a process.
  In this mode, public symbols have to be explicitly marked in the source code
  to be exported from shared libraries. This is the recommended mode.
+
By default compiler default visibility mode is used (no compiler flags are added).
+
NOTE: In Boost super-project Jamroot file this property is set to the default
value of `hidden`. This means that Boost libraries are built with hidden
visibility by default, unless the user overrides it with a different `visibility`
or a library sets a different `local-visibility` (see below).

[[bbv2.builtin.features.local-visibility]]`local-visibility`::
*Allowed values:* `global`, `protected`, `hidden`.
+
This feature has the same effect as the `visibility` feature but is intended
to be used by targets that require a particular symbol visibility. Unlike
the `visibility` feature, `local-visibility` is not inherited by the target
dependencies and only affects the target to which it is applied.
+
The `local-visibility` feature supports the same values with the same meaning
as the `visibility` feature. By default, if `local-visibility` is not specified
for a target, the value of the `visibility` feature is used.

[[bbv2.reference.tools]]
== Builtin tools

Boost.Build comes with support for a large number of {CPP} compilers, and
other tools. This section documents how to use those tools.

Before using any tool, you must declare your intention, and possibly
specify additional information about the tool's configuration. This is
done by calling the `using` rule, typically in your `user-config.jam`,
for example:

[source]
----
using gcc ;
----

additional parameters can be passed just like for other rules, for
example:

[source]
----
using gcc : 4.0 : g++-4.0 ;
----

The options that can be passed to each tool are documented in the
subsequent sections.

[[bbv2.reference.tools.compilers]]
=== {CPP} Compilers

This section lists all Boost.Build modules that support {CPP} compilers
and documents how each one can be initialized. The name of support
module for compiler is also the value for the `toolset` feature that can
be used to explicitly request that compiler.

:leveloffset: +3
include::../../src/tools/acc.jam[tag=doc]
include::../../src/tools/borland.jam[tag=doc]
include::../../src/tools/como.jam[tag=doc]
include::../../src/tools/cw.jam[tag=doc]
include::../../src/tools/dmc.jam[tag=doc]
include::../../src/tools/gcc.jam[tag=doc]
include::../../src/tools/hp_cxx.jam[tag=doc]
include::../../src/tools/intel.jam[tag=doc]
include::../../src/tools/msvc.jam[tag=doc]
include::../../src/tools/sun.jam[tag=doc]
include::../../src/tools/vacpp.jam[tag=doc]
:leveloffset: -3

=== Third-party libraries

Boost.Build provides special support for some third-party {CPP} libraries,
documented below.

[[bbv2.reference.tools.libraries.stlport]]
==== STLport library

The http://stlport.org[STLport] library is an alternative implementation
of {CPP} runtime library. Boost.Build supports using that library on
Windows platform. Linux is hampered by different naming of libraries in
each STLport version and is not officially supported.

Before using STLport, you need to configure it in `user-config.jam`
using the following syntax:

[source]
----
using stlport : version : header-path : library-path ;
----

Where version is the version of STLport, for example `5.1.4`, headers is
the location where STLport headers can be found, and libraries is the
location where STLport libraries can be found. The version should always
be provided, and the library path should be provided if you're using
STLport's implementation of `iostreams`. Note that STLport 5.* always uses
its own `iostream` implementation, so the library path is required.

When STLport is configured, you can build with STLport by requesting
`stdlib=stlport` on the command line.

[[bbv2.reference.tools.libraries.zlib]]
==== zlib

Provides support for the http://www.zlib.net[zlib] library. zlib can be
configured either to use precompiled binaries or to build the library
from source.

zlib can be initialized using the following syntax

[source]
----
using zlib : version : options : condition : is-default ;
----

Options for using a prebuilt library:

`search`::
  The directory containing the zlib binaries.
`name`::
  Overrides the default library name.
`include`::
  The directory containing the zlib headers.

If none of these options is specified, then the environmental variables
ZLIB_LIBRARY_PATH, ZLIB_NAME, and ZLIB_INCLUDE will be used instead.

Options for building zlib from source:

`source`::
  The zlib source directory. Defaults to the environmental variable
  ZLIB_SOURCE.
`tag`::
  Sets the link:#bbv2.builtin.features.tag[tag] property to adjust the
  file name of the library. Ignored when using precompiled binaries.
`build-name`::
  The base name to use for the compiled library. Ignored when using
  precompiled binaries.

Examples:

[source]
----
# Find zlib in the default system location
using zlib ;
# Build zlib from source
using zlib : 1.2.7 : <source>/home/steven/zlib-1.2.7 ;
# Find zlib in /usr/local
using zlib : 1.2.7 : <include>/usr/local/include <search>/usr/local/lib ;
# Build zlib from source for msvc and find
# prebuilt binaries for gcc.
using zlib : 1.2.7 : <source>C:/Devel/src/zlib-1.2.7 : <toolset>msvc ;
using zlib : 1.2.7 : : <toolset>gcc ;
----

[[bbv2.reference.tools.libraries.bzip2]]
==== bzip2

Provides support for the http://www.bzip.org[bzip2] library. bzip2 can
be configured either to use precompiled binaries or to build the library
from source.

bzip2 can be initialized using the following syntax

[source]
----
using bzip2 : version : options : condition : is-default ;
----

Options for using a prebuilt library:

`search`::
  The directory containing the bzip2 binaries.
`name`::
  Overrides the default library name.
`include`::
  The directory containing the bzip2 headers.

If none of these options is specified, then the environmental variables
BZIP2_LIBRARY_PATH, BZIP2_NAME, and BZIP2_INCLUDE will be used instead.

Options for building bzip2 from source:

`source`::
  The bzip2 source directory. Defaults to the environmental variable
  BZIP2_SOURCE.
`tag`::
  Sets the link:#bbv2.builtin.features.tag[tag] property to adjust the
  file name of the library. Ignored when using precompiled binaries.
`build-name`::
  The base name to use for the compiled library. Ignored when using
  precompiled binaries.

Examples:

[source]
----
# Find bzip in the default system location
using bzip2 ;
# Build bzip from source
using bzip2 : 1.0.6 : <source>/home/sergey/src/bzip2-1.0.6 ;
# Find bzip in /usr/local
using bzip2 : 1.0.6 : <include>/usr/local/include <search>/usr/local/lib ;
# Build bzip from source for msvc and find
# prebuilt binaries for gcc.
using bzip2 : 1.0.6 : <source>C:/Devel/src/bzip2-1.0.6 : <toolset>msvc ;
using bzip2 : 1.0.6 : : <toolset>gcc ;
----

[[bbv2.reference.tools.libraries.python]]
==== Python

Provides support for the http://www.python.org[python] language
environment to be linked in as a library.

python can be initialized using the following syntax

[source]
----
using python : [version] : [command-or-prefix] : [includes] : [libraries] : [conditions] : [extension-suffix] ;
----

Options for using python:

`version`::
The version of Python to use. Should be in Major.Minor format, for example
2.3. Do not include the sub-minor version.

`command-or-prefix`::
Preferably, a command that invokes a Python interpreter. Alternatively, the
installation prefix for Python libraries and includes. If empty, will be
guessed from the version, the platform's installation patterns, and the
python executables that can be found in PATH.

`includes`::
the include path to Python headers. If empty, will be guessed.

`libraries`::
the path to Python library binaries. If empty, will be guessed. On
MacOS/Darwin, you can also pass the path of the Python framework.

`conditions`::
if specified, should be a set of properties that are matched against the
build configuration when Boost.Build selects a Python configuration to use.

`extension-suffix`::
A string to append to the name of extension modules before the true filename
extension. Ordinarily we would just compute this based on the value of the
`<python-debugging>` feature. However ubuntu's `python-dbg` package uses the
windows convention of appending _d to debug-build extension modules. We have
no way of detecting ubuntu, or of probing python for the "_d" requirement,
and if you configure and build python using `--with-pydebug`, you'll be using
the standard *nix convention. Defaults to "" (or "_d" when targeting windows
and <python-debugging> is set).

Examples:

[source]
----
# Find python in the default system location
using python ;
# 2.7
using python : 2.7 ;
# 3.5
using python : 3.5 ;

# On ubuntu 16.04
using python
: 2.7 # version
: # Interpreter/path to dir
: /usr/include/python2.7 # includes
: /usr/lib/x86_64-linux-gnu # libs
: # conditions
;

using python 
: 3.5 # version
: # Interpreter/path to dir
: /usr/include/python3.5 # includes
: /usr/lib/x86_64-linux-gnu # libs
: # conditions
;

# On windows
using python
: 2.7 # version
: C:\\Python27-32\\python.exe # Interperter/path to dir
: C:\\Python27-32\\include # includes
: C:\\Python27-32\\libs # libs
: <address-model>32 <address-model> # conditions - both 32 and unspecified 
;

using python
: 2.7 # version
: C:\\Python27-64\\python.exe # Interperter/path to dir
: C:\\Python27-64\\include # includes
: C:\\Python27-64\\libs # libs
: <address-model>64 # conditions
;
----

=== Documentation tools

Boost.Build support for the Boost documentation tools is documented
below.

[[bbv2.reference.tools.doc.xsltproc]]
==== xsltproc

To use xsltproc, you first need to configure it using the following
syntax:

[source]
----
using xsltproc : xsltproc ;
----

Where xsltproc is the xsltproc executable. If xsltproc is not specified,
and the variable XSLTPROC is set, the value of XSLTPROC will be used.
Otherwise, xsltproc will be searched for in PATH.

The following options can be provided, using
_`<option-name>option-value syntax`_:

`xsl:param`::
  Values should have the form name=value
`xsl:path`::
  Sets an additional search path for xi:include elements.
`catalog`::
  A catalog file used to rewrite remote URL's to a local copy.

The xsltproc module provides the following rules. Note that these
operate on jam targets and are intended to be used by another toolset,
such as boostbook, rather than directly by users.

`xslt`::
+
----
rule xslt ( target : source stylesheet : properties * )
----
+
Runs xsltproc to create a single output file.

`xslt-dir`::
+
----
rule xslt-dir ( target : source stylesheet : properties * : dirname )
----
+
Runs xsltproc to create multiple outputs in a directory. `dirname` is
unused, but exists for historical reasons. The output directory is
determined from the target.

[[bbv2.reference.tools.doc.boostbook]]
==== boostbook

To use boostbook, you first need to configure it using the following
syntax:

[source]
----
using boostbook : docbook-xsl-dir : docbook-dtd-dir : boostbook-dir ;
----

`docbook-xsl-dir` is the DocBook XSL stylesheet directory. If not
provided, we use `DOCBOOK_XSL_DIR` from the environment (if available) or
look in standard locations. Otherwise, we let the XML processor load the
stylesheets remotely.

`docbook-dtd-dir` is the DocBook DTD directory. If not provided, we use
`DOCBOOK_DTD_DIR` From the environment (if available) or look in standard
locations. Otherwise, we let the XML processor load the DTD remotely.

`boostbook-dir` is the BoostBook directory with the DTD and XSL sub-dirs.

The boostbook module depends on xsltproc. For pdf or ps output, it also
depends on fop.

The following options can be provided, using
_`<option-name>option-value syntax`_:

`format`::
+
*Allowed values:* `html`, `xhtml`, `htmlhelp`, `onehtml`, `man`,
`pdf`, `ps`, `docbook`, `fo`, `tests`.
+
The `format` feature determines the type of output produced by the
boostbook rule.

The boostbook module defines a rule for creating a target following the
common syntax.

`boostbook`::
+
----
rule boostbook ( target-name : sources * : requirements * : default-build * )
----
+
Creates a boostbook target.

[[bbv2.reference.tools.doc.doxygen]]
==== doxygen

To use doxygen, you first need to configure it using the following
syntax:

[source]
----
using doxygen : name ;
----

`name` is the doxygen command. If it is not specified, it will be found in
the PATH.

The doxygen module depends on the boostbook module when generating
BoostBook XML.

The following options can be provided, using
_`<option-name>option-value syntax`_:

`doxygen:param`::
+
All the values of `doxygen:param` are added to the `doxyfile`.

`prefix`::
+
Specifies the common prefix of all headers when generating BoostBook
XML. Everything before this will be stripped off.

`reftitle`::
+
Specifies the title of the library-reference section, when generating
BoostBook XML.

`doxygen:xml-imagedir`::
+
When generating BoostBook XML, specifies the directory in which to
place the images generated from LaTex formulae.
+
WARNING: The path is interpreted relative to the current working directory,
not relative to the Jamfile. This is necessary to match the behavior of
BoostBook.

The doxygen module defines a rule for creating a target following the
common syntax.

`doxygen`::
+
----
rule doxygen ( target : sources * : requirements * : default-build * : usage-requirements * )
----
+
Creates a doxygen target. If the target name ends with .html, then
this will generate an html directory. Otherwise it will generate
BoostBook XML.

[[bbv2.reference.tools.doc.quickbook]]
==== quickbook

The quickbook module provides a generator to convert from Quickbook to
BoostBook XML.

To use quickbook, you first need to configure it using the following
syntax:

[source]
----
using quickbook : command ;
----

`command` is the quickbook executable. If it is not specified, Boost.Build
will compile it from source. If it is unable to find the source it will
search for a quickbook executable in PATH.

[[bbv2.reference.tools.doc.fop]]
==== fop

The fop module provides generators to convert from XSL formatting
objects to Postscript and PDF.

To use fop, you first need to configure it using the following syntax:

[source]
----
using fop : fop-command : java-home : java ;
----

`fop-command` is the command to run fop. If it is not specified,
Boost.Build will search for it in PATH and FOP_HOME.

Either `java-home` or `java` can be used to specify where to find java.

[[bbv2.reference.modules]]
== Builtin modules

This section describes the modules that are provided by Boost.Build. The
import rule allows rules from one module to be used in another module or
Jamfile.

[[bbv2.reference.modules.modules]]
=== modules

The `modules` module defines basic functionality for handling modules.

A module defines a number of rules that can be used in other modules.
Modules can contain code at the top level to initialize the module. This
code is executed the first time the module is loaded.

NOTE: A Jamfile is a special kind of module which is managed by the build
system. Although they cannot be loaded directly by users, the other
features of modules are still useful for Jamfiles.

Each module has its own namespaces for variables and rules. If two
modules A and B both use a variable named X, each one gets its own copy
of X. They won't interfere with each other in any way. Similarly,
importing rules into one module has no effect on any other module.

Every module has two special variables. `$(__file__)` contains the name
of the file that the module was loaded from and `$(__name__)` contains
the name of the module.

NOTE: `$(__file__)` does not contain the full path to the file. If you need
this, use `modules.binding`.

1. `rule binding ( module-name )`
+
Returns the filesystem binding of the given module.
+
For example, a module can get its own location with:
+
[source,jam]
----
me = [ modules.binding $(__name__) ] ;
----

2. `rule poke ( module-name ? : variables + : value * )`
+
Sets the module-local value of a variable.
+
For example, to set a variable in the global module:
+
[source,jam]
----
modules.poke : ZLIB_INCLUDE : /usr/local/include ;
----

3. `rule peek ( module-name ? : variables + )`
+
Returns the module-local value of a variable.
+
For example, to read a variable from the global module:
+
[source,jam]
----
local ZLIB_INCLUDE = [ modules.peek : ZLIB_INCLUDE ] ;
----

4. `rule call-in ( module-name ? : rule-name args * : * )`
+
Call the given rule locally in the given module. Use this for rules
accepting rule names as arguments, so that the passed rule may be
invoked in the context of the rule's caller (for example, if the rule
accesses module globals or is a local rule).
+
NOTE: rules called this way may accept at most 8 parameters.
+
Example:
+
[source,jam]
----
rule filter ( f : values * )
{
    local m = [ CALLER_MODULE ] ;
    local result ;
    for v in $(values)
    {
        if [ modules.call-in $(m) : $(f) $(v) ]
        {
            result += $(v) ;
        }
    }
    return result ;
}
----

5. `rule load ( module-name : filename ? : search * )`
+
Load the indicated module if it is not already loaded.
+
`module-name`::
  Name of module to load.
+
`filename`::
  (partial) path to file; Defaults to `$(module-name).jam`
+
`search`::
  Directories in which to search for filename. Defaults to
  `$(BOOST_BUILD_PATH)`.

6. `rule import ( module-names + : rules-opt * : rename-opt * )`
+
Load the indicated module and import rule names into the current module.
Any members of `rules-opt` will be available without qualification in
the caller's module. Any members of `rename-opt` will be taken as the
names of the rules in the caller's module, in place of the names they
have in the imported module. If `rules-opt = '*'`, all rules from the
indicated module are imported into the caller's module. If `rename-opt`
is supplied, it must have the same number of elements as `rules-opt`.
+
NOTE: The `import` rule is available without qualification in all modules.
+
Examples:
+
[source,jam]
----
import path ;
import path : * ;
import path : join ;
import path : native make : native-path make-path ;
----

7. `rule clone-rules ( source-module target-module )`
+
Define exported copies in `$(target-module)` of all rules exported from
`$(source-module)`. Also make them available in the global module with
qualification, so that it is just as though the rules were defined
originally in `$(target-module)`.

:leveloffset: +2

include::path.adoc[]

include::regex.adoc[]

include::sequence.adoc[]

include::type.adoc[]

:leveloffset: -2

[[bbv2.reference.class]]
== Builtin classes

:leveloffset: +2

include::abstract-target.adoc[]

include::project-target.adoc[]

include::main-target.adoc[]

include::basic-target.adoc[]

include::typed-target.adoc[]

include::property-set.adoc[]

:leveloffset: -2

[[bbv2.reference.buildprocess]]
== Build process

The general overview of the build process was given in the
link:#bbv2.overview.build_process[user documentation]. This section
provides additional details, and some specific rules.

To recap, building a target with specific properties includes the
following steps:

1.  applying the default build,
2.  selecting the main target alternative to use,
3.  determining the "common" properties,
4.  building targets referred by the the sources list and dependency
properties,
5.  adding the usage requirements produced when building dependencies to
the "common" properties,
6.  building the target using generators,
7.  computing the usage requirements to be returned.

[[bbv2.reference.buildprocess.alternatives]]
=== Alternative selection

When a target has several alternatives, one of them must be selected.
The process is as follows:

1.  For each alternative, its _condition_ is defined as the set of
link:#bbv2.reference.features.attributes.base[base properties] in its
requirements. link:#bbv2.reference.variants.propcond[Conditional
properties] are excluded.

2.  An alternative is viable only if all properties in its condition are
present in the build request.

3.  If there's only one viable alternative, it's chosen. Otherwise, an
attempt is made to find the best alternative. An alternative a is better
than another alternative b, if the set of properties in b's condition is
a strict subset of the set of properties of a's condition. If one viable
alternative is better than all the others, it's selected. Otherwise, an
error is reported.

[[bbv2.reference.buildprocess.common]]
=== Determining common properties

"Common" properties is a somewhat artificial term. This is the
intermediate property set from which both the build request for
dependencies and the properties for building the target are derived.

Since the default build and alternatives are already handled, we have
only two inputs: the build request and the requirements. Here are the
rules about common properties.

1.  Non-free features can have only one value

2.  A non-conditional property in the requirements is always present in
common properties.

3.  A property in the build request is present in common properties,
unless it is overridden by a property in the requirements.

4.  If either the build request, or the requirements (non-conditional or
conditional) include an expandable property (either composite, or with a
specified sub-feature value), the behavior is equivalent to explicitly
adding all the expanded properties to the build request or the
requirements respectively.

5.  If the requirements include a
link:#bbv2.reference.variants.propcond[conditional property], and the
condition of this property is true in the context of common properties,
then the conditional property should be in common properties as well.

6.  If no value for a feature is given by other rules here, it has
default value in common properties.

These rules are declarative. They don't specify how to compute the
common properties. However, they provide enough information for the
user. The important point is the handling of conditional requirements.
The condition can be satisfied either by a property in the build
request, by non-conditional requirements, or even by another conditional
property. For example, the following example works as expected:

[source]
----
exe a : a.cpp
      : <toolset>gcc:<variant>release
        <variant>release:<define>FOO ;
----

[[bbv2.reference.buildprocess.targetpath]]
=== Target Paths

Several factors determine the location of a concrete file target. All
files in a project are built under the directory bin unless this is
overridden by the build-dir project attribute. Under bin is a path that
depends on the properties used to build each target. This path is
uniquely determined by all non-free, non-incidental properties. For
example, given a property set containing: `<toolset>gcc`
`<toolset-gcc:version>4.6.1` `<variant>debug` `<warnings>all` `<define>_DEBUG`
`<include>/usr/local/include` `<link>static`, the path will be
`gcc-4.6.1/debug/link-static`. `<warnings>` is an incidental feature and
`<define>` and `<include>` are free features, so they do not affect the path.

Sometimes the paths produced by Boost.Build can become excessively long.
There are a couple of command line options that can help with this.
`--abbreviate-paths` reduces each element to no more than five characters.
For example, `link-static` becomes `lnk-sttc`. The `--hash` option reduces the
path to a single directory using an MD5 hash.

There are two features that affect the build directory. The `<location>`
feature completely overrides the default build directory. For example,

[source]
----
exe a : a.cpp : <location>. ;
----

builds all the files produced by `a` in the directory of the Jamfile.
This is generally discouraged, as it precludes variant builds.

The <location-prefix> feature adds a prefix to the path, under the
project's build directory. For example,

[source]
----
exe a : a.cpp : <location-prefix>subdir ;
----

will create the files for `a` in `bin/subdir/gcc-4.6.1/debug`

[[bbv2.reference.definitions]]
== Definitions

[[bbv2.reference.features]]
=== Features and properties

A _feature_ is a normalized (toolset-independent) aspect of a build
configuration, such as whether inlining is enabled. Feature names may
not contain the '`>`' character.

Each feature in a build configuration has one or more associated
__value__s. Feature values for non-free features may not contain the
punctuation characters of pointy bracket (‘`<`’), colon (‘`:`’ ),
equal sign (‘`=`’) and dashes (‘`-`’). Feature values for free
features may not contain the pointy bracket (‘`<`’) character.

A _property_ is a (feature,value) pair, expressed as <feature>value.

A _subfeature_ is a feature that only exists in the presence of its
parent feature, and whose identity can be derived (in the context of its
parent) from its value. A subfeature's parent can never be another
subfeature. Thus, features and their subfeatures form a two-level
hierarchy.

A _value-string_ for a feature *F* is a string of the form
`value-subvalue1-subvalue2`...`-subvalueN`, where `value` is a legal
value for *F* and `subvalue1`...`subvalueN` are legal values of some of
*F*'s subfeatures separated with dashes (‘`-`’).
For example, the properties `<toolset>gcc <toolset-version>3.0.1` can
be expressed more concisely using a value-string, as `<toolset>gcc-3.0.1`.

A _property set_ is a set of properties (i.e. a collection without
duplicates), for instance: `<toolset>gcc <runtime-link>static`.

A _property path_ is a property set whose elements have been joined into
a single string separated by slashes. A property path representation of
the previous example would be `<toolset>gcc/<runtime-link>static`.

A _build specification_ is a property set that fully describes the set
of features used to build a target.

[[bbv2.reference.features.validity]]
=== Property Validity

For link:#bbv2.reference.features.attributes.free[free] features, all
values are valid. For all other features, the valid values are
explicitly specified, and the build system will report an error for the
use of an invalid feature-value. Subproperty validity may be restricted
so that certain values are valid only in the presence of certain other
subproperties. For example, it is possible to specify that the
`<gcc-target>mingw` property is only valid in the presence of
`<gcc-version>2.95.2`.

[[bbv2.reference.features.attributes]]
=== Feature Attributes

Each feature has a collection of zero or more of the following
attributes. Feature attributes are low-level descriptions of how the
build system should interpret a feature's values when they appear in a
build request. We also refer to the attributes of properties, so that an
_incidental_ property, for example, is one whose feature has the
_incidental_ attribute.

* [[bbv2.reference.features.attributes.incidental]] _incidental_
+
Incidental features are assumed not to affect build products at all. As
a consequence, the build system may use the same file for targets whose
build specification differs only in incidental features. A feature that
controls a compiler's warning level is one example of a likely
incidental feature.
+
Non-incidental features are assumed to affect build products, so the
files for targets whose build specification differs in non-incidental
features are placed in different directories as described in
<<bbv2.reference.buildprocess.targetpath>>.

* [[bbv2.reference.features.attributes.propagated]] _propagated_
+
Features of this kind are propagated to dependencies. That is, if a
link:#bbv2.overview.targets.main[main target] is built using a
propagated property, the build systems attempts to use the same property
when building any of its dependencies as part of that main target. For
instance, when an optimized executable is requested, one usually wants
it to be linked with optimized libraries. Thus, the `<optimization>`
feature is propagated.

* [[bbv2.reference.features.attributes.free]] _free_
+
Most features have a finite set of allowed values, and can only take on
a single value from that set in a given build specification. Free
features, on the other hand, can have several values at a time and each
value can be an arbitrary string. For example, it is possible to have
several preprocessor symbols defined simultaneously:
+
----
<define>NDEBUG=1 <define>HAS_CONFIG_H=1
----

* [[bbv2.reference.features.attributes.optional]] _optional_
+
An optional feature is a feature that is not required to appear in a
build specification. Every non-optional non-free feature has a default
value that is used when a value for the feature is not otherwise
specified, either in a target's requirements or in the user's build
request. [A feature's default value is given by the first value listed
in the feature's declaration. -- move this elsewhere - dwa]

* [[bbv2.reference.features.attributes.symmetric]] _symmetric_
+
Normally a feature only generates a sub-variant directory when its value
differs from its default value, leading to an asymmetric sub-variant
directory structure for certain values of the feature. A symmetric
feature always generates a corresponding sub-variant directory.

* [[bbv2.reference.features.attributes.path]] _path_
+
The value of a path feature specifies a path. The path is treated as
relative to the directory of Jamfile where path feature is used and is
translated appropriately by the build system when the build is invoked
from a different directory

* [[bbv2.reference.features.attributes.implicit]] _implicit_
+
Values of implicit features alone identify the feature. For example, a
user is not required to write "<toolset>gcc", but can simply write
"gcc". Implicit feature names also don't appear in variant paths,
although the values do. Thus: bin/gcc/... as opposed to
bin/toolset-gcc/.... There should typically be only a few such features,
to avoid possible name clashes.

* [[bbv2.reference.features.attributes.composite]] _composite_
+
Composite features actually correspond to groups of properties. For
example, a build variant is a composite feature. When generating targets
from a set of build properties, composite features are recursively
expanded and _added_ to the build property set, so rules can find them
if necessary. Non-composite non-free features override components of
composite features in a build property set.

* [[bbv2.reference.features.attributes.dependency]] _dependency_
+
The value of a dependency feature is a target reference. When used for
building of a main target, the value of dependency feature is treated as
additional dependency.
+
For example, dependency features allow to state that library A depends
on library B. As the result, whenever an application will link to A, it
will also link to B. Specifying B as dependency of A is different from
adding B to the sources of A.

[[bbv2.reference.features.attributes.base]]
Features that are neither free nor incidental are called _base_
features.

[[bbv2.reference.features.declaration]]
=== Feature Declaration

The low-level feature declaration interface is the `feature` rule from
the `feature` module:

[source]
----
rule feature ( name : allowed-values * : attributes * )
----

A feature's allowed-values may be extended with the `feature.extend`
rule.

[[bbv2.reference.variants.proprefine]]
=== Property refinement

When a target with certain properties is requested, and that target
requires some set of properties, it is needed to find the set of
properties to use for building. This process is called _property
refinement_ and is performed by these rules

1.  Each property in the required set is added to the original property
set

2.  If the original property set includes property with a different
value of non free feature, that property is removed.

[[bbv2.reference.variants.propcond]]
=== Conditional properties

Sometime it's desirable to apply certain requirements only for a
specific combination of other properties. For example, one of compilers
that you use issues a pointless warning that you want to suppress by
passing a command line option to it. You would not want to pass that
option to other compilers. Conditional properties allow you to do just
that. Their syntax is:

----
property ( "," property ) * ":" property
----

For example, the problem above would be solved by:

[source]
----
exe hello : hello.cpp : <toolset>yfc:<cxxflags>-disable-pointless-warning ;
----

The syntax also allows several properties in the condition, for example:

[source]
----
exe hello : hello.cpp : <os>NT,<toolset>gcc:<link>static ;
----

[[bbv2.reference.ids]]
=== Target identifiers and references

_Target identifier_ is used to denote a target. The syntax is:

----
target-id -> (target-name | file-name | project-id | directory-name)
              | (project-id | directory-name) "//" target-name
project-id -> path
target-name -> path
file-name -> path
directory-name -> path
----

This grammar allows some elements to be recognized as either

* name of target declared in current Jamfile (note that target names may
include slash).
* a regular file, denoted by absolute name or name relative to project's
sources location.
* project id (at this point, all project ids start with slash).
* the directory of another project, denoted by absolute name or name
relative to the current project's location.

To determine the real meaning the possible interpretations are checked
in this order. For example, valid target ids might be:

|===
| `a`                                    | target in current project
| `lib/b.cpp`                            | regular file
| `/boost/thread`                        | project "/boost/thread"
| `/home/ghost/build/lr_library//parser` | target in specific project
| `../boost_1_61_0`                      | project in specific directory
|===

**Rationale:**Target is separated from project by special separator (not
just slash), because:

* It emphasis that projects and targets are different things.
* It allows to have main target names with slashes.

[[bbv2.reference.targets.references]]
_Target reference_ is used to specify a source target, and may
additionally specify desired properties for that target. It has this
syntax:

----
target-reference -> target-id [ "/" requested-properties ]
requested-properties -> property-path
----

For example,

[source]
----
exe compiler : compiler.cpp libs/cmdline/<optimization>space ;
----

would cause the version of `cmdline` library, optimized for space, to be
linked in even if the `compiler` executable is build with optimization
for speed.
