[[b2.reference]]
= Reference

[[b2.reference.general]]
== General information

[[b2.reference.init]]
=== Initialization

Immediately upon starting, the B2 engine (*`b2`*) loads the Jam
code that implements the build system. To do this, it searches for the
build system `bootstrap.jam` file in specific installation locations.
The search is based on the location of the `b2(.exe)` executable
location.

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

NOTE: To maintain backward compatibility the file called
`boost-build.jam`, is loaded if present. The search starts 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. On Unix BOOST_BUILD_PATH defaults to `/usr/share/b2`.

[[b2.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.

[[b2.reference.rules.exe]]`exe`::
Creates an executable file. See
link:#b2.tasks.programs[the section called “Programs”].

[[b2.reference.rules.lib]]`lib`::
Creates an library file. See
link:#b2.tasks.libraries[the section called “Libraries”].

[[b2.reference.rules.install]]`install`::
Installs built targets and other files. See
link:#b2.tasks.installing[the section called “Installing”].

[[b2.reference.rules.alias]]`alias`::
Creates an alias for other targets. See
link:#b2.tasks.alias[the section called “Alias”].

[[b2.reference.rules.unit-test]]`unit-test`::
Creates an executable that will be automatically run. See
link:#b2.builtins.testing[the section called “Testing”].

[[b2.reference.rules.test]]`compile`; `compile-fail`; `link`; `link-fail`; `run`; `run-fail`::
Specialized rules for testing. See
link:#b2.builtins.testing[the section called “Testing”].

[[b2.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 ] ;
----

[[b2.reference.rules.obj]]`obj`::
Creates an object file. Useful when a single source file must be
compiled with special properties.

[[b2.reference.rules.preprocessed]]`preprocessed`::
Creates an preprocessed source file. The arguments follow the
link:#b2.main-target-rule-syntax[common syntax].

[[b2.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 ] ;
----

[[b2.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.

[[b2.reference.rules.project]]`project`::
Declares project id and attributes, including project requirements.
See link:#b2.overview.projects[the section called “Projects”].

[[b2.reference.rules.use-project]]`use-project`::
Assigns a symbolic project ID to a project at a given path. This rule
must be better documented!

[[b2.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.

[[b2.reference.rules.always]]`always`::
The `always` function takes a single parameter—a list of metatarget
names. The 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 it will always be recompiled. Note that
if a build of `hello` is not requested, for example you specify just
`bye` on the command line, `hello` will not be recompiled.

[[b2.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 ;
----

[[b2.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`.

[[b2.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.

[[b2.reference.rules.test-suite]]`test-suite`::
This rule is deprecated and equivalent to `alias`.

[[b2.reference.rules.import-search]]`import-search`::
+
====
[horizontal]
Jam:: `rule import-search ( reference )`
====
+
Adds the given `reference` path to the set of directories that an `import` will
search. The `reference` can be a plain directory or a known project path. If a
project path is given it will be searched for and resolved to include any
sub-project path in the reference. If a directory is given it will be rooted
relative to the current project location. Example project path usage:
+
----
import-search /boost/config/checks ;
import-search /boost/predef/tools/checks ;
----
+

:leveloffset: +1

include::../../src/engine/mod_jam_builtin.h[tag=reference]

:leveloffset: -1

[[b2.overview.builtins.features]]
== Builtin features

This section documents the features that are built-in into B2.
For features with a fixed set of values, that set is provided, with the
default value listed first.

include::../../src/tools/features/address-model-feature.jam[tag=doc]
include::../../src/tools/features/sanitizers-feature.jam[tag=addr-doc]
include::../../src/tools/features/allow-feature.jam[tag=doc]
include::../../src/tools/features/architecture-feature.jam[tag=doc]
include::../../src/tools/features/archiveflags-feature.jam[tag=doc]
include::../../src/tools/features/asmflags-feature.jam[tag=doc]
include::../../src/tools/features/exception-feature.jam[tag=asynch-doc]
include::../../src/tools/features/build-feature.jam[tag=doc]
include::../../src/tools/features/cflags-feature.jam[tag=doc]
include::../../src/tools/features/compileflags-feature.jam[tag=doc]
include::../../src/tools/features/conditional-feature.jam[tag=doc]
include::../../src/tools/features/coverage-feature.jam[tag=doc]
include::../../src/tools/features/cxxflags-feature.jam[tag=doc]
include::../../src/tools/features/cxxstd-feature.jam[tag=doc]
include::../../src/tools/features/cxxabi-feature.jam[tag=doc]
include::../../src/tools/features/cxx-template-depth-feature.jam[tag=doc]
include::../../src/tools/features/debug-feature.jam[tag=doc]
include::../../src/tools/features/define-feature.jam[tag=doc]
include::../../src/tools/features/dll-feature.jam[tag=def-doc]
include::../../src/tools/features/dependency-feature.jam[tag=doc]
include::../../src/tools/features/dll-feature.jam[tag=doc]
include::../../src/tools/msvc.jam[tag=embed-doc]
include::../../src/tools/features/exception-feature.jam[tag=doc]
include::../../src/tools/features/fflags-feature.jam[tag=doc]
include::../../src/tools/features/file-feature.jam[tag=doc]
include::../../src/tools/features/find-lib-feature.jam[tag=doc]
include::../../src/tools/features/flags-feature.jam[tag=doc]
include::../../src/tools/features/dll-feature.jam[tag=hardcode-doc]
include::../../src/tools/features/dependency-feature.jam[tag=impl-doc]
include::../../src/tools/features/force-include-feature.jam[tag=doc]
include::../../src/tools/features/include-feature.jam[tag=doc]
include::../../src/tools/features/optimization-feature.jam[tag=inline-doc]
include::../../src/tools/stage.jam[tag=features-install-package-doc]
include::../../src/tools/stage.jam[tag=features-install-prefix-doc]
include::../../src/tools/features/instruction-set-feature.jam[tag=doc]
include::../../src/tools/features/library-feature.jam[tag=doc]
include::../../src/tools/features/find-lib-feature.jam[tag=path-doc]
include::../../src/tools/features/sanitizers-feature.jam[tag=leak-doc]
include::../../src/tools/features/linemarkers-feature.jam[tag=doc]
include::../../src/tools/features/link-feature.jam[tag=doc]
include::../../src/tools/features/linkflags-feature.jam[tag=doc]
include::../../src/tools/features/local-visibility-feature.jam[tag=doc]
include::../../src/tools/features/location-feature.jam[tag=doc]
include::../../src/tools/features/location-prefix-feature.jam[tag=doc]
include::../../src/tools/features/objcflags-feature.jam[tag=doc]
include::../../src/tools/features/name-feature.jam[tag=doc]
include::../../src/tools/features/optimization-feature.jam[tag=doc]
include::../../src/tools/features/debug-feature.jam[tag=prof-doc]
include::../../src/tools/features/relevant-feature.jam[tag=doc]
include::../../src/tools/features/rtti-feature.jam[tag=doc]
include::../../src/tools/features/runtime-feature.jam[tag=doc]
include::../../src/tools/features/search-feature.jam[tag=doc]
include::../../src/tools/features/source-feature.jam[tag=doc]
include::../../src/tools/stage.jam[tag=features-staging-prefix-doc]
include::../../src/tools/features/stdlib-feature.jam[tag=doc]
include::../../src/tools/features/strip-feature.jam[tag=doc]
include::../../src/tools/features/dll-feature.jam[tag=suppress-doc]
include::../../src/tools/features/tag-feature.jam[tag=doc]
include::../../src/tools/features/os-feature.jam[tag=doc]
include::../../src/tools/features/threadapi-feature.jam[tag=doc]
include::../../src/tools/features/threading-feature.jam[tag=doc]
include::../../src/tools/features/sanitizers-feature.jam[tag=thread-doc]
include::../../src/tools/features/toolset-feature.jam[tag=doc]
include::../../src/tools/features/define-feature.jam[tag=undef-doc]
include::../../src/tools/features/sanitizers-feature.jam[tag=undef-doc]
include::../../src/tools/features/dependency-feature.jam[tag=use-doc]
include::../../src/tools/features/user-interface-feature.jam[tag=doc]
include::../../src/tools/features/variant-feature.jam[tag=doc]
include::../../src/tools/features/optimization-feature.jam[tag=vector-doc]
include::../../src/tools/features/version-feature.jam[tag=doc]
include::../../src/tools/features/visibility-feature.jam[tag=doc]
include::../../src/tools/features/warnings-feature.jam[tag=doc]
include::../../src/tools/features/translate-path-feature.jam[tag=doc]
include::../../src/tools/features/lto-feature.jam[tag=doc]
include::../../src/tools/features/response-file-feature.jam[tag=doc]

[[b2.reference.tools]]
== Builtin tools

B2 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.

[[b2.reference.tools.compilers]]
=== {CPP} Compilers

This section lists all B2 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/cc.jam[tag=doc]
include::../../src/tools/clang-linux.jam[tag=doc]
include::../../src/tools/clang-win.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/embarcadero.jam[tag=doc]
include::../../src/tools/emscripten.jam[tag=doc]
include::../../src/tools/gcc.jam[tag=doc]
include::../../src/tools/hp_cxx.jam[tag=doc]
include::../../src/tools/ibmcxx.jam[tag=doc]
include::../../src/tools/intel.jam[tag=doc]
include::../../src/tools/msvc.jam[tag=doc]
include::../../src/tools/sun.jam[tag=doc]
:leveloffset: -3

=== Third-party libraries

B2 provides special support for some third-party {CPP} libraries,
documented below.

[[b2.reference.tools.libraries.stlport]]
==== STLport library

The http://stlport.org[STLport] library is an alternative implementation
of {CPP} runtime library. B2 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.

[[b2.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:#b2.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 ;
----

[[b2.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:#b2.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 ;
----

[[b2.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 B2 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

B2 support for the Boost documentation tools is documented
below.

[[b2.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.

[[b2.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.

[[b2.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.

[[b2.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, B2
will compile it from source. If it is unable to find the source it will
search for a quickbook executable in PATH.

[[b2.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,
B2 will search for it in PATH and FOP_HOME.

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

[[b2.reference.modules]]
== Builtin modules

This section describes the modules that are provided by B2. The
import rule allows rules from one module to be used in another module or
Jamfile.

:leveloffset: +2

include::../../src/engine/mod_jam_modules.h[tag=reference]
include::../../src/engine/mod_jam_class.h[tag=reference]
include::../../src/engine/mod_jam_errors.h[tag=reference]
include::../../src/engine/mod_regex.h[tag=reference]
include::../../src/engine/mod_set.h[tag=reference]
include::../../src/engine/mod_string.h[tag=reference]
include::../../src/engine/mod_version.h[tag=reference]
include::../../src/engine/mod_db.h[tag=reference]
include::../../src/engine/mod_args.h[tag=reference]

include::path.adoc[]

include::sequence.adoc[]

include::../../src/tools/stage.jam[tag=doc]

include::type.adoc[]

:leveloffset: -2

[[b2.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

[[b2.reference.buildprocess]]
== Build process

The general overview of the build process was given in the
link:#b2.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.

[[b2.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:#b2.reference.features.attributes.base[base properties] in its
requirements. link:#b2.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.

[[b2.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:#b2.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 ;
----

[[b2.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 B2 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`

[[b2.reference.definitions]]
== Definitions

[[b2.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.

[[b2.reference.features.validity]]
=== Property Validity

For link:#b2.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`.

[[b2.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.

* [[b2.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
<<b2.reference.buildprocess.targetpath>>.

* [[b2.reference.features.attributes.propagated]] _propagated_
+
Features of this kind are propagated to dependencies. That is, if a
link:#b2.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.

* [[b2.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
----

* [[b2.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]

* [[b2.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.

* [[b2.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

* [[b2.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.

* [[b2.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.

* [[b2.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.

[[b2.reference.features.attributes.base]]
Features that are neither free nor incidental are called _base_
features.

[[b2.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.

[[b2.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.

[[b2.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 ;
----

[[b2.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.

[[b2.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.
