...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
This section describes main targets types that Boost.Build supports out-of-the-box. Unless otherwise noted, all mentioned main target rules have the common signature, described in the section called “Declaring Targets”.
Programs are created using the exe
rule, which follows the
common syntax. For
example:
exe hello : hello.cpp some_library.lib /some_project//library : <threading>multi ;
This will create an executable file from the sources—in this case, one C++ file, one library file present in the same directory, and another library that is created by Boost.Build. Generally, sources can include C and C++ files, object files and libraries. Boost.Build will automatically try to convert targets of other types.
Tip | |
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On Windows, if an application uses shared libraries, and both the
application and the libraries are built using Boost.Build, it is not
possible to immediately run the application, because the |
Library targets are created using the lib
rule, which
follows the common syntax
. For example:
lib helpers : helpers.cpp ;
This will define a library target named helpers
built from
the helpers.cpp
source file.
It can be either a static library or a shared library,
depending on the value of the <link> feature.
Library targets can represent:
Libraries that should be built from source, as in the example above.
Prebuilt libraries which already exist on the system.
Such libraries can be searched for by the tools using them (typically
with the linker's -l
option) or their paths can be
known in advance by the build system.
The syntax for prebuilt libraries is given below:
lib z : : <name>z <search>/home/ghost ; lib compress : : <file>/opt/libs/compress.a ;
The name
property specifies the name of the library
without the standard prefixes and suffixes. For example, depending
on the system, z
could refer to a file called
z.so, libz.a, or z.lib, etc. The search
feature
specifies paths in which to search for the library in addition
to the default compiler paths. search
can be specified
several times or it can be omitted, in which case only the default
compiler paths will be searched. The file
property
specifies the file location.
The difference between using the file
feature and
using a combination of the name
and search
features is that file
is more precise.
Warning | |
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The value of the lib a : : <name>a <search>/pool/release ; lib b : : <name>b <search>/pool/debug ;
If /pool/release/a.so, /pool/release/b.so, /pool/debug/a.so,
and /pool/release/b.so all exist, the linker will probably
take both |
For convenience, the following syntax is allowed:
lib z ; lib gui db aux ;
which has exactly the same effect as:
lib z : : <name>z ; lib gui : : <name>gui ; lib db : : <name>db ; lib aux : : <name>aux ;
When a library references another library you should put that other library in its list of sources. This will do the right thing in all cases. For portability, you should specify library dependencies even for searched and prebuilt libraries, othewise, static linking on Unix will not work. For example:
lib z ; lib png : z : <name>png ;
Note | |
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When a library has a shared library as a source, or a static library has another static library as a source then any target linking to the first library with automatically link to its source library as well. On the other hand, when a shared library has a static library as a source then the first library will be built so that it completely includes the second one. If you do not want a shared library to include all the libraries specified in its sources (especially statically linked ones), you would need to use the following: lib b : a.cpp ; lib a : a.cpp : <use>b : : <library>b ;
This specifies that library |
Usage requirements are often
very useful for defining library targets. For example, imagine that
you want you build a helpers
library and its interface is
described in its helpers.hpp
header file located in the same
directory as the helpers.cpp
source file. Then you could add
the following to the Jamfile located in that same directory:
lib helpers : helpers.cpp : : : <include>. ;
which would automatically add the directory where the target has been
defined (and where the library's header file is located) to the compiler's
include path for all targets using the helpers
library. This
feature greatly simplifies Jamfiles.
The alias
rule gives an alternative name to a
group of targets. For example, to give the name core
to a group of three other targets with the following code:
alias core : im reader writer ;
Using core
on the command line, or in the source list
of any other target is the same as explicitly using im
, reader
, and writer
.
Another use of the alias
rule is to change build properties.
For example, if you want to use link statically to the Boost Threads
library, you can write the following:
alias threads : /boost/thread//boost_thread : <link>static ;
and use only the threads
alias in your Jamfiles.
You can also specify usage requirements for the alias
target.
If you write the following:
alias header_only_library : : : : <include>/usr/include/header_only_library ;
then using header_only_library
in sources will only add an
include path. Also note that when an alias has sources, their usage
requirements are propagated as well. For example:
lib library1 : library1.cpp : : : <include>/library/include1 ; lib library2 : library2.cpp : : : <include>/library/include2 ; alias static_libraries : library1 library2 : <link>static ; exe main : main.cpp static_libraries ;
will compile main.cpp
with additional includes
required for using the specified static libraries.
This section describes various ways to install built target and arbitrary files.
For installing a built target you should use the install
rule, which follows the
common syntax. For example:
install dist : hello helpers ;
will cause the targets hello
and helpers
to be
moved to the dist
directory, relative to the
Jamfile's directory. The directory can be changed using the
location
property:
install dist : hello helpers : <location>/usr/bin ;
While you can achieve the same effect by changing the target name to
/usr/bin
, using the location
property is
better as it allows you to use a mnemonic target name.
The location
property is especially handy when the location
is not fixed, but depends on the build variant or environment variables:
install dist : hello helpers : <variant>release:<location>dist/release <variant>debug:<location>dist/debug ; install dist2 : hello helpers : <location>$(DIST) ;
See also conditional properties and environment variables
Specifying the names of all libraries to install can be boring. The
install
allows you to specify only the top-level executable
targets to install, and automatically install all dependencies:
install dist : hello : <install-dependencies>on <install-type>EXE <install-type>LIB ;
will find all targets that hello
depends on, and install all
of those which are either executables or libraries. More specifically, for
each target, other targets that were specified as sources or as dependency
properties, will be recursively found. One exception is that targets
referred with the
use
feature are not considered, as that feature is
typically used to refer to header-only libraries. If the set of target
types is specified, only targets of that type will be installed,
otherwise, all found target will be installed.
By default, the install
rule will strip paths from its
sources. So, if sources include a/b/c.hpp
, the
a/b
part will be ignored. To make the
install
rule preserve the directory hierarchy you need to
use the <install-source-root>
feature to specify
the root of the hierarchy you are installing. Relative paths from that
root will be preserved. For example, if you write:
install headers : a/b/c.h : <location>/tmp <install-source-root>a ;
the a file named /tmp/b/c.h
will be created.
The glob-tree rule can be used to find all files below a given directory, making it easy to install an entire directory tree.
The alias
rule can be
used when targets need to be installed into several directories:
alias install : install-bin install-lib ; install install-bin : applications : /usr/bin ; install install-lib : helper : /usr/lib ;
Because the install
rule just copies targets, most free
features [12] have no
effect when used in requirements of the install
rule. The
only two that matter are
dependency
and, on Unix, dll-path
.
Note | |
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(Unix specific) On Unix, executables built using Boost.Build typically
contain the list of paths to all used shared libraries. For installing,
this is not desired, so Boost.Build relinks the executable with an empty
list of paths. You can also specify additional paths for installed
executables using the |
Boost.Build has convenient support for running unit tests. The simplest
way is the unit-test
rule, which follows the common syntax. For example:
unit-test helpers_test : helpers_test.cpp helpers ;
The unit-test
rule behaves like the
exe rule, but after the executable is created
it is also run. If the executable returns an error code, the build system
will also return an error and will try running the executable on the next
invocation until it runs successfully. This behaviour ensures that you can
not miss a unit test failure.
By default, the executable is run directly. Sometimes, it is desirable to
run the executable using some helper command. You should use the
testing.launcher
property to specify the name of the helper
command. For example, if you write:
unit-test helpers_test
: helpers_test.cpp helpers
: <testing.launcher>valgrind
;
The command used to run the executable will be:
valgrind bin/$toolset/debug/helpers_test
There are few specialized testing rules, listed below:
rule compile ( sources : requirements * : target-name ? ) rule compile-fail ( sources : requirements * : target-name ? ) rule link ( sources + : requirements * : target-name ? ) rule link-fail ( sources + : requirements * : target-name ? )
They are given a list of sources and requirements. If the target name is
not provided, the name of the first source file is used instead. The
compile*
tests try to compile the passed source. The
link*
rules try to compile and link an application from
all the passed sources. The compile
and link
rules expect that compilation/linking succeeds. The
compile-fail
and link-fail
rules expect that
the compilation/linking fails.
There are two specialized rules for running applications, which are more
powerful than the unit-test
rule. The run
rule
has the following signature:
rule run ( sources + : args * : input-files * : requirements * : target-name ? : default-build * )
The rule builds application from the provided sources and runs it, passing
args
and input-files
as command-line
arguments. The args
parameter is passed verbatim and
the values of the input-files
parameter are treated as
paths relative to containing Jamfile, and are adjusted if bjam
is invoked from a different directory. The
run-fail
rule is identical to the run
rule,
except that it expects that the run fails.
All rules described in this section, if executed successfully, create a
special manifest file to indicate that the test passed. For the
unit-test
rule the files is named
and for the other rules it is
called
target-name
.passed
.
The target-name
.testrun*
rules also capture all output from the program, and
store it in a file named
.
target-name
.output
If the preserve-test-targets
feature has the value
off
, then run
and the run-fail
rules will remove the executable after running it. This somewhat decreases
disk space requirements for continuous testing environments. The default
value of preserve-test-targets
feature is on
.
It is possible to print the list of all test targets (except for
unit-test
) declared in your project, by passing the
--dump-tests
command-line option. The output will consist of
lines of the form:
boost-test(test-type
)path
:sources
It is possible to process the list of tests, Boost.Build output
and the presense/absense of the *.test
files created when test passes into human-readable status table of tests.
Such processing utilities are not included in Boost.Build.
For most main target rules, Boost.Build automatically figures out the commands to run. When you want to use new file types or support new tools, one approach is to extend Boost.Build to support them smoothly, as documented in the section called “Extender Manual”. However, if the new tool is only used in a single place, it might be easier just to specify the commands to run explicitly.
Three main target rules can be used for that. The make
rule allows you to construct a single file from any number
of source file, by running a command you specify. The
notfile
rule allows you to run an arbitrary command,
without creating any files. And finaly, the generate
rule allows you to describe a transformation using
Boost.Build's virtual targets. This is higher-level than the file names that
the make
rule operates with and allows you to
create more than one target, create differently named targets depending on
properties or use more than one tool.
The make
rule is used when you want to create
one file from a number of sources using some specific command. The
notfile
is used to unconditionally run a
command.
Suppose you want to create the file file.out
from
the file file.in
by running the command
in2out. Here is how you would do this in Boost.Build:
make file.out : file.in : @in2out ; actions in2out { in2out $(<) $(>) }
If you run b2 and file.out
does
not exist, Boost.Build will run the in2out command to
create that file. For more details on specifying actions, see the section called “Boost.Jam Language”.
It could be that you just want to run some command unconditionally, and
that command does not create any specific files. For that you can use the
notfile
rule. For example:
notfile echo_something : @echo ; actions echo { echo "something" }
The only difference from the make
rule is
that the name of the target is not considered a name of a file, so
Boost.Build will unconditionally run the action.
The generate
rule is used when you want to
express transformations using Boost.Build's virtual targets, as opposed to
just filenames. The generate
rule has the
standard main target rule signature, but you are required to specify the
generating-rule
property. The value of the property
should be in the form
@
, the named rule should
have the following signature:
rule-name
rule generating-rule ( project name : property-set : sources * )
and will be called with an instance of the project-target
class, the name of the main target, an instance of the
property-set
class containing build properties, and the list
of instances of the virtual-target
class corresponding to
sources. The rule must return a list of virtual-target
instances. The interface of the virtual-target
class can be
learned by looking at the build/virtual-target.jam
file. The generate
example contained in the
Boost.Build distribution illustrates how the generate
rule can be used.
Precompiled headers is a mechanism to speed up compilation by creating a partially processed version of some header files, and then using that version during compilations rather then repeatedly parsing the original headers. Boost.Build supports precompiled headers with gcc and msvc toolsets.
To use precompiled headers, follow the following steps:
Create a header that includes headers used by your project that you
want precompiled. It is better to include only headers that are
sufficiently stable — like headers from the compiler and
external libraries. Please wrap the header in #ifdef
BOOST_BUILD_PCH_ENABLED
, so that the potentially expensive
inclusion of headers is not done when PCH is not enabled. Include the
new header at the top of your source files.
Declare a new Boost.Build target for the precompiled header and add that precompiled header to the sources of the target whose compilation you want to speed up:
cpp-pch pch : pch.hpp ; exe main : main.cpp pch ;
You can use the c-pch
rule if you want to
use the precompiled header in C programs.
The pch
example in Boost.Build distribution can be
used as reference.
Please note the following:
The inclusion of the precompiled header must be the first thing in a source file, before any code or preprocessor directives.
The build properties used to compile the source files and the precompiled header must be the same. Consider using project requirements to assure this.
Precompiled headers must be used purely as a way to improve
compilation time, not to save the number of #include
statements. If a source file needs to include some header, explicitly
include it in the source file, even if the same header is included
from the precompiled header. This makes sure that your project will
build even if precompiled headers are not supported.
On the gcc compiler, the name of the header being precompiled must be
equal to the name of the cpp-pch
target. This is a gcc
requirement.
Prior to version 4.2, the gcc compiler did not allow anonymous namespaces in precompiled headers, which limits their utility. See the bug report for details.
Usually, Boost.Build handles implicit dependendies completely
automatically. For example, for C++ files, all #include
statements are found and handled. The only aspect where user help might be
needed is implicit dependency on generated files.
By default, Boost.Build handles such dependencies within one main target. For example, assume that main target "app" has two sources, "app.cpp" and "parser.y". The latter source is converted into "parser.c" and "parser.h". Then, if "app.cpp" includes "parser.h", Boost.Build will detect this dependency. Moreover, since "parser.h" will be generated into a build directory, the path to that directory will automatically added to include path.
Making this mechanism work across main target boundaries is possible, but
imposes certain overhead. For that reason, if there is implicit dependency
on files from other main targets, the <implicit-dependency>
feature must be used, for example:
lib parser : parser.y ; exe app : app.cpp : <implicit-dependency>parser ;
The above example tells the build system that when scanning all sources of "app" for implicit-dependencies, it should consider targets from "parser" as potential dependencies.
Boost.Build supports cross compilation with the gcc and msvc toolsets.
When using gcc, you first need to specify your cross compiler
in user-config.jam
(see the section called “Configuration”),
for example:
using gcc : arm : arm-none-linux-gnueabi-g++ ;
After that, if the host and target os are the same, for example Linux, you can just request that this compiler version to be used:
b2 toolset=gcc-arm
If you want to target different operating system from the host, you need
to additionally specify the value for the target-os
feature, for
example:
# On windows box b2 toolset=gcc-arm target-os=linux # On Linux box b2 toolset=gcc-mingw target-os=windows
For the complete list of allowed opeating system names, please see the documentation for target-os feature.
When using the msvc compiler, it's only possible to cross-compiler to a 64-bit system on a 32-bit host. Please see the section called “64-bit support” for details.