This section will provide the information necessary to create your own projects using Boost.Build. The information provided here is relatively high-level, and as well as the on-line help system must be used to obtain low-level documentation (see ). Boost.Build actually consists of two parts - Boost.Jam, a build engine with its own interpreted language, and Boost.Build itself, implemented in Boost.Jam's language. The chain of events when you type bjam on the command line is: Boost.Jam tries to find Boost.Build and loads the top-level module. The exact process is described in The top-level module loads user-defined configuration files, user-config.jam and site-config.jam, which define available toolsets. The Jamfile in the current directory is read. That in turn might cause reading of further Jamfiles. As a result, a tree of projects is created, with targets inside projects. Finally, using the build request specified on the command line, Boost.Build decides which targets should be built, and how. That information is passed back to Boost.Jam, which takes care of actually running commands. So, to be able to successfully use Boost.Build, you need to know only four things: How to configure Boost.Build How to write Jamfiles How the build process works Some Basics about the Boost.Jam language. See also the Boost.Jam documentation.

This section will describe the basics of the Boost.Jam language—just enough for writing Jamfiles. For more information, please see the Boost.Jam documentation. Boost.Jam has an interpreted, procedural language. On the lowest level, a Boost.Jam program consists of variables and rule rules (the Jam term for function). They are grouped in modules—there's one global module and a number of named modules. Besides that, a Boost.Jam program contains classes and class instances. Syntantically, a Boost.Jam program consists of two kind of elements—keywords (which have a special meaning to Boost.Jam) and literals. Consider this code: a = b ; which assigns the value b to the variable a. Here, = and ; are keywords, while a and b are literals. All syntax elements, even keywords, must be separated by spaces. For example, omitting the space character before ; will lead to a syntax error. If you want to use a literal value that is the same as some keyword, the value can be quoted: a = "=" ; All variables in Boost.Jam have the same type—list of strings. To define a variable one assigns a value to it, like in the previous example. An undefined variable is the same as a variable with an empty value. Variables can be accessed with the $(variable) syntax. For example: a = $(b) $(c) ; Rules are defined by specifying the rule name, the parameter names, and the allowed size of the list value for each parameter. rule example ( parameter1 : parameter2 ? : parameter3 + : parameter4 * ) { // body } When this rule is called, the list passed as the first argument must have exactly one value. The list passed as the second argument can either have one value of be empty. The two remaining arguments can be arbitrary long, but the third argument may not be empty. The overview of Boost.Jam language statements is given below: helper 1 : 2 : 3 ; x = [ helper 1 : 2 : 3 ] ; This code calls the named rule with the specified arguments. When the result of the call must be used inside some expression, you need to add brackets around the call, like shown on the second line. if cond { statements } [ else { statements } ] This is a regular if-statement. The condition is composed of: Literals (true if at least one string is not empty) Comparisons: a operator b where operator is one of =, !=, <, >, <=, >=. The comparison is done pairwise between each string in the left and the right arguments. Logical operations: ! a, a && b, a || b Grouping: ( cond ) for var in list { statements } Executes statements for each element in list, setting the variable var to the element value. while cond { statements } Repeatedly execute statements while cond remains true upon entry. return values ; This statement should be used only inside a rule and assigns values to the return value of the rule. The return statement does not exit the rule. For example: rule test ( ) { if 1 = 1 { return "reasonable" ; } return "strange" ; } will return strange, not reasonable. import module ; import module : rule ; The first form imports the specified bjam module. All rules from that module are made available using the qualified name: module.rule. The second form imports the specified rules only, and they can be called using unqualified names. Sometimes, you'd need to specify the actual command lines to be used when creating targets. In jam language, you use named actions to do this. For example: actions create-file-from-another { create-file-from-another $(<) $(>) } This specifies a named action called create-file-from-another. The text inside braces is the command to invoke. The $(<) variable will be expanded to list of generated files, and the $(>) variable will be expanded to the list of source files. To flexibly adjust command line, you can define a rule with the same name as the action, and taking three parameters -- targets, sources and properties. For example: rule create-file-from-another ( targets * : sources * : properties * ) { if <variant>debug in $(properties) { OPTIONS on $(targets) = --debug ; } } actions create-file-from-another { create-file-from-another $(OPTIONS) $(<) $(>) } In this example, the rule checks if certain build property is specified. If so, it sets variable OPIONS that's used inside action. Note that the variable is set "on targets" -- the value will be only visible inside action, not globally. Were it set globally, using variable named OPTIONS in two unrelated actions would be impossible. More details can be found in Jam reference,

The Boost.Build configuration is specified in the file user-config.jam. You can edit the one in the top-level directory of Boost.Build installation or create a copy in your home directory and edit that. (See for the exact search paths.) The primary function of that file is to declare which compilers and other tools are available. The simplest syntax to configure a tool is: using tool-name ; The using rule is given a name of tool, and will make that tool available to Boost.Build. For example, using gcc ; will make the gcc compiler available. Since nothing but a tool name is specified, Boost.Build will pick some default settings. For example, it will use the gcc executable found in the PATH, or look in some known installation locations. In most cases, this strategy works automatically. In case you have several versions of a compiler, it's installed in some unusual location, or you need to tweak its configuration, you'll need to pass additional parameters to the using rule. The parameters to using can be different for each tool. You can obtain specific documentation for any tool's configuration parameters by invoking bjam --help tool-name.init That said, for all the compiler toolsets Boost.Build supports out-of-the-box, the list of parameters to using is the same: toolset-name, version, invocation-command, and options. The version parameter identifies the toolset version, in case you have several installed. It can have any form you like, but it's recommended that you use a numeric identifier like 7.1. The invocation-command parameter is the command that must be executed to run the compiler. This parameter can usually be omitted if the compiler executable has its “usual name” and is in the PATH, or was installed in a standard “installation directory”, or can be found through a global mechanism like the Windows registry. For example: using msvc : 7.1 ; using gcc ; If the compiler can be found in the PATH but only by a nonstandard name, you can just supply that name: using gcc : : g++-3.2 ; Otherwise, it might be necessary to supply the complete path to the compiler executable: using msvc : : "Z:/Programs/Microsoft Visual Studio/vc98/bin/cl" ; Some Boost.Build toolsets will use that path to take additional actions required before invoking the compiler, such as calling vendor-supplied scripts to set up its required environment variables. When compiler executables for C and C++ are different, path to the C++ compiler executable must be specified. The “invocation command” can be any command allowed by the operating system. For example: using msvc : : echo Compiling && foo/bar/baz/cl ; will work. To configure several versions of a toolset, simply invoke the using rule multiple times: using gcc : 3.3 ; using gcc : 3.4 : g++-3.4 ; using gcc : 3.2 : g++-3.2 ; Note that in the first call to using, the compiler found in the PATH will be used, and there's no need to explicitly specify the command. As shown above, both the version and invocation-command parameters are optional, but there's an important restriction: if you configure the same toolset more than once, you must pass the version parameter every time. For example, the following is not allowed: using gcc ; using gcc : 3.4 : g++-3.4 ; because the first using call does not specify a version. The options parameter is used to fine-tune the configuration. All of Boost.Build's standard compiler toolsets accept properties of the four builtin features cflags, cxxflags, compileflags and linkflags as options specifying flags that will be always passed to the corresponding tools. Values of the cflags feature are passed directly to the C compiler, values of the cxxflags feature are passed directly to the C++ compiler, and values of the compileflags feature are passed to both. For example, to configure a gcc toolset so that it always generates 64-bit code you could write: using gcc : 3.4 : : <compileflags>-m64 <linkflags>-m64 ;

This section describes how invoke Boost.Build from the command line To build all targets defined in Jamfile in the current directory with default properties, run: bjam To build specific targets, specify them on the command line: bjam lib1 subproject//lib2 To request a certain value for some property, add property=value to the command line: bjam toolset=gcc variant=debug optimization=space For often used features, like toolset and variant you can omit the feature name, so the above can be written as: bjam optimization=space Boost.Build recognizes the following command line options. --clean Cleans all targets in the current directory and in any subprojects. Note that unlike the clean target in make, you can use --clean together with target names to clean specific targets. --clean-all Cleans all targets, no matter where they are defined. In particular, it will clean targets in parent Jamfiles, and targets defined under other project roots. --build-dir Changes build directories for all project roots being built. When this option is specified, all Jamroot files should declare project name. The build directory for the project root will be computed by concatanating the value of the --build-dir option, the project name specified in Jamroot, and the build dir specified in Jamroot (or bin, if none is specified). The option is primarily useful when building from read-only media, when you can't modify Jamroot. --version Prints information on Boost.Build and Boost.Jam versions. --help Invokes the online help system. This prints general information on how to use the help system with additional --help* options. --debug-configuration Produces debug information about loading of Boost.Build and toolset files. --debug-building Prints what targets are being built and with what properties. --debug-generators Produces debug output from generator search process. Useful for debugging custom generators. --ignore-config Do not load site-config.jam and user-config.jam configuration files. --debug Enables internal checks. For complete specification of command line syntax, see

A Main target is a user-defined named entity that can be built, for example an executable file. Declaring a main target is usually done using one of the main target rules described in . The user can also declare custom main target rules as shown in . main targetdeclaration syntax Most main target rules in Boost.Build have the same common signature: common signature rule rule-name ( main-target-name : sources + : requirements * : default-build * : usage-requirements * ) main-target-name is the name used to request the target on command line and to use it from other main targets. A main target name may contain alphanumeric characters, dashes (‘-’), and underscores (‘_’). sources is the list of source files and other main targets that must be combined. requirements is the list of properties that must always be present when this main target is built. default-build is the list of properties that will be used unless some other value of the same feature is already specified, e.g. on the command line or by propogation from a dependent target. usage-requirements is the list of properties that will be propagated to all main targets that use this one, i.e. to all its dependents. Some main target rules have a different list of parameters, their documentation explicitly says so. The actual requirements for a target are obtained by refining requirements of the project where a target is declared with the explicitly specified requirements. The same is true for usage-requirements. More details can be found in

The name of main target has two purposes. First, it's used to refer to this target from other targets and from command line. Second, it's used to compute the names of the generated files. Typically, filenames are obtained from main target name by appending system-dependent suffixes and prefixes. Name of main target can contain alphanumeral characters, dash, undescore and dot. The entire name is significant when resolving references from other targets. For determining filenames, only the part before the first dot is taken. For example: obj test.release : test.cpp : <variant>release ; obj test.debug : test.cpp : <variant>debug ; will generate two files named test.obj (in two different directories), not two files named test.release.obj and test.debug.obj.

The list of sources specifies what should be processed to get the resulting targets. Most of the time, it's just a list of files. Sometimes, you'll want to automatically construct the list of source files rather than having to spell it out manually, in which case you can use the glob rule. Here are two examples: exe a : a.cpp ; # a.cpp is the only source file exe b : [ glob *.cpp ] ; # all .cpp files in this directory are sources Unless you specify a file with an absolute path, the name is considered relative to the source directory—which is typically the directory where the Jamfile is located, but can be changed as described in . The list of sources can also refer to other main targets. Targets in the same project can be referred to by name, while targets in other projects must be qualified with a directory or a symbolic project name. The directory/project name is separated from the target name by double slash. There's no special syntax to distinguish directory name from project name—the part before double slash is first looked up as project name, and then as directory name. For example: lib helper : helper.cpp ; exe a : a.cpp helper ; # Since all project ids start with slash, ".." is directory name. exe b : b.cpp ..//utils ; exe c : c.cpp /boost/program_options//program_options ; The first exe uses the library defined in the same project. The second one uses some target (most likely library) defined by Jamfile one level higher. Finally, the third target uses some C++ Boost library, referring to it by absolute symbolic name. More information about target references can be found in and .

Requirements are the properties that should always be present when building a target. Typically, they are includes and defines: exe hello : hello.cpp : <include>/opt/boost <define>MY_DEBUG ; There is a number of other features, listed in . For example if a library can only be built statically, or a file can't be compiled with optimization due to a compiler bug, one can use lib util : util.cpp : <link>static ; obj main : main.cpp : <optimization>off ; Sometimes, particular relationships need to be maintained among a target's build properties. This can be achieved with conditional requirements. For example, you might want to set specific #defines when a library is built as shared, or when a target's release variant is built in release mode. lib network : network.cpp : <link>shared:<define>NEWORK_LIB_SHARED <variant>release:<define>EXTRA_FAST ; In the example above, whenever network is built with <link>shared, <define>NEWORK_LIB_SHARED will be in its properties, too. You can use several properties in the condition, for example: lib network : network.cpp : <toolset>gcc,<optimization>speed:<define>USE_INLINE_ASSEMBLER ; More powerfull variant of conditional requirements is indirect conditional requiremens. You can provide a rule that will be called with the current build properties and can compute additional properties to be added. For example: lib network : network.cpp : <conditional>@my-rule ; rule my-rule ( properties * ) { local result ; if <toolset>gcc <optimization>speed in $(properties) { result += <define>USE_INLINE_ASSEMBLER ; } return $(result) ; } This example is equivalent to the previous one, but for complex cases, indirect conditional requirements can be easier to write and understand.

The default-build parameter is a set of properties to be used if the build request does not otherwise specify a value for features in the set. For example: exe hello : hello.cpp : : <threading>multi ; would build a multi-threaded target in unless the user explicitly requests a single-threaded version. The difference between requirements and default-build is that requirements cannot be overriden in any way.

The ways a target is built can be so different that describing them using conditional requirements would be hard. For example, imagine that a library actually uses different source files depending on the toolset used to build it. We can express this situation using target alternatives: lib demangler : dummy_demangler.cpp ; # alternative 1 lib demangler : demangler_gcc.cpp : <toolset>gcc ; # alternative 2 lib demangler : demangler_msvc.cpp : <toolset>msvc ; # alternative 3 In the example above, when built with gcc or msvc, demangler will use a source file specific to the toolset. Otherwise, it will use a generic source file, dummy_demangler.cpp. It is possible to declare a target inline, i.e. the "sources" parameter may include calls to other main rules. For example: exe hello : hello.cpp [ obj helpers : helpers.cpp : <optimization>off ] ; Will cause "helpers.cpp" to be always compiled without optimization. When referring to an inline main target, its declared name must be prefixed by its parent target's name and two dots. In the example above, to build only helpers, one should run bjam hello..helpers. When no target is requested on the command line, all targets in the current project will be built. If a target should be built only by explicit request, this can be expressed by the explicit rule: explicit install_programs ;

As mentioned before, targets are grouped into projects, and each Jamfile is a separate project. Projects are useful because they allow us to group related targets together, define properties common to all those targets, and assign a symbolic name to the project that can be used in referring to its targets. Projects are named using the project rule, which has the following syntax: project id : attributes ; Here, attributes is a sequence of rule arguments, each of which begins with an attribute-name and is followed by any number of build properties. The list of attribute names along with its handling is also shown in the table below. For example, it is possible to write: project tennis : requirements <threading>multi : default-build release ; The possible attributes are listed below. Project id is a short way to denote a project, as opposed to the Jamfile's pathname. It is a hierarchical path, unrelated to filesystem, such as "boost/thread". Target references make use of project ids to specify a target. Source location specifies the directory where sources for the project are located. Project requirements are requirements that apply to all the targets in the projects as well as all subprojects. Default build is the build request that should be used when no build request is specified explicitly. The default values for those attributes are given in the table below. The following table describes utility rules that can be used in Jamfiles. Detailed information for any of these rules can be obtained by running: bjam --help project.rulename When you've described your targets, you want Boost.Build to run the right tools and create the needed targets. This section will describe two things: how you specify what to build, and how the main targets are actually constructed. The most important thing to note is that in Boost.Build, unlike other build tools, the targets you declare do not correspond to specific files. What you declare in a Jamfile is more like a “metatarget.” Depending on the properties you specify on the command line, each metatarget will produce a set of real targets corresponding to the requested properties. It is quite possible that the same metatarget is built several times with different properties, producing different files. This means that for Boost.Build, you cannot directly obtain a build variant from a Jamfile. There could be several variants requested by the user, and each target can be built with different properties.

The command line specifies which targets to build and with which properties. For example: bjam app1 lib1//lib1 toolset=gcc variant=debug optimization=full would build two targets, "app1" and "lib1//lib1" with the specified properties. You can refer to any targets, using target id and specify arbitrary properties. Some of the properties are very common, and for them the name of the property can be omitted. For example, the above can be written as: bjam app1 lib1//lib1 gcc debug optimization=full The complete syntax, which has some additional shortcuts, is described in .

When you request, directly or indirectly, a build of a main target with specific requirements, the following steps are done. Some brief explanation is provided, and more details are given in . Applying default build. If the default-build property of a target specifies a value of a feature that is not present in the build request, that value is added. Selecting the main target alternative to use. For each alternative we look how many properties are present both in alternative's requirements, and in build request. The alternative with large number of matching properties is selected. Determining "common" properties. The build request is refined with target's requirements. The conditional properties in requirements are handled as well. Finally, default values of features are added. Building targets referred by the sources list and dependency properties. The list of sources and the properties can refer to other target using target references. For each reference, we take all propagated properties, refine them by explicit properties specified in the target reference, and pass the resulting properties as build request to the other target. Adding the usage requirements produced when building dependencies to the "common" properties. When dependencies are built in the previous step, they return both the set of created "real" targets, and usage requirements. The usage requirements are added to the common properties and the resulting property set will be used for building the current target. Building the target using generators. To convert the sources to the desired type, Boost.Build uses "generators" --- objects that correspond to tools like compilers and linkers. Each generator declares what type of targets it can produce and what type of sources it requires. Using this information, Boost.Build determines which generators must be run to produce a specific target from specific sources. When generators are run, they return the "real" targets. Computing the usage requirements to be returned. The conditional properties in usage requirements are expanded and the result is returned.

Often, a user builds a complete project, not just one main target. In fact, invoking bjam without arguments builds the project defined in the current directory. When a project is built, the build request is passed without modification to all main targets in that project. It's is possible to prevent implicit building of a target in a project with the explicit rule: explicit hello_test ; would cause the hello_test target to be built only if explicitly requested by the user or by some other target. The Jamfile for a project can include a number of build-project rule calls that specify additional projects to be built.

This section describes main targets types that Boost.Build supports of-of-the-box. Unless otherwise noted, all mentioned main target rules have the common signature, described in .

Builtin rulesexe 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. On Windows, if an application uses dynamic libraries, and both the application and the libraries are built by Boost.Build, its not possible to immediately run the application, because the PATH environment variable should include the path to the libraries. It means you have to either add the paths manually, or place the application and the libraries to the same directory, for example using the stage rule.

Libraries are created using the lib rule, which follows the common syntax. For example: lib helpers : helpers.cpp : <include>boost : : <include>. ; In the most common case, the lib creates a library from the specified sources. Depending on the value of <link> feature the library will be either static or shared. There are two other cases. First is when the library is installed somewhere in compiler's search paths, and should be searched by the compiler (typically, using the -l option). The second case is where the library is available as a prebuilt file and the full path is known. The syntax for these case is given below: lib z : : <name>z <search>/home/ghost ; lib compress : : <file>/opt/libs/compress.a ; The name property specifies the name that should be passed to the -l option, and the file property specifies the file location. The search feature specifies paths in which to search for the library. That feature can be specified several times, or it can be omitted, in which case only default compiler paths will be searched. The difference between using the file feature as opposed to the name feature together with the search feature is that file is more precise. A specific file will be used. On the other hand, the search feature only adds a library path, and the name feature gives the basic name of the library. The search rules are specific to the linker. For example, given these definition: lib a : : <variant>release <file>/pool/release/a.so ; lib a : : <variant>debug <file>/pool/debug/a.so ; lib b : : <variant>release <file>/pool/release/b.so ; lib b : : <variant>debug <file>/pool/debug/b.so ; It's possible to use release version of a and debug version of b. Had we used the name and search features, the linker would always pick either release or debug versions. For convenience, the following syntax is allowed: lib z ; lib gui db aux ; and is does exactly the same as: lib z : : <name>z ; lib gui : : <name>gui ; lib db : : <name>db ; lib aux : : <name>aux ; When a library uses another library you should put that other library in the 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 won't work. For example: lib z ; lib png : z : <name>png ; When a library (say, a), that has another library, (say, b) is linked dynamically, the b library will be incorporated in a. (If b is dynamic library as well, then a will only refer to it, and not include any extra code.) When the a library is linked statically, Boost.Build will assure that all executables that link to a will also link to b. One feature of Boost.Build that is very important for libraries is usage requirements. For example, if you write: lib helpers : helpers.cpp : : : <include>. ; then the compiler include path for all targets that use helpers will contain the directory where the target is defined.path to "helpers.cpp". The user only needs to add helpers to the list of sources, and needn't consider the requirements its use imposes on a dependent target. This feature greatly simplifies Jamfiles. If you don't want shared libraries to include all libraries that are specified in sources (especially statically linked ones), you'd need to use the following: lib b : a.cpp ; lib a : a.cpp : <use>b : : <library>b ; This specifies that a uses b, and causes all executables that link to a also link to b. In this case, even for shared linking, the a library won't even refer to b.

The alias rule gives 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, but it is just more convenient. Another use of the alias rule is to change build properties. For example, if you always want static linking for a specific C++ Boost 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 there are some sources, their usage requirements are propagated, too. For example: lib lib : lib.cpp : : : <include>. ; alias lib_alias ; exe main : main.cpp lib_alias ; will compile main.cpp with the additional include.

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 Jamfile's directory. The directory can be changed with 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, because it allows you to use a mnemonic target name. The location property is especially handy when the location is not fixed, but depends on 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, because 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. The alias rule can be used when targets must 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 see the definition of "free" in . have no effect when used in requirements of the install rule. The only two which matter are dependency and, on Unix, dll-path. (Unix specific). On Unix, executables built with Boost.Build typically contain the list of paths to all used dynamic 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 with the dll-path feature.

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 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't miss a unit test failure. By default, the executable is run directly. Sometimes, it's 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 rules for more elaborate testing: compile, compile-fail, run and run-fail. They are more suitable for automated testing, and are not covered here.

Sometimes, the builtin target types are not enough, and you want Boost.Build to just run specific commands. There are two main target rules that make it possible: make and notfile. 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 file file.out from file file.in by running command in2out. Here's how you'd do this in Boost.Build: actions in2out { in2out $(<) $(>) } make file.out : file.in : @in2out ; If you run bjam 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 make rule is useful to express custom transformation that are used just once or twice in your project. For transformations that are used often, you are advised to declare new generator, as described in . It could be that you just want to run some command unconditionally, and that command does not create any specific files. The, 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.

variant A feature that combines several low-level features, making it easy to request common build configurations. Allowed values: debug, release, profile. 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 User can define his own build variants using the variant rule from the common module. Notee: Runtime debugging is on in debug builds to suit the expectations of people used to various IDEs. link A feature that controls how libraries are built. Allowed values: shared, static source The <source>X feature has the same effect on building a target as putting X in the list of sources. It's 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 ) See also the <library> feature. 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. 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. For example, in application with plugins, the plugins are not used when linking the application, application might have dependency on its plugins, even though , and adds its usage requirements to the build properties of the target being declared. The primary use case is when you want the usage requirements (such as #include paths) of some library to be applied, but don't want to link to it. 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 don't want to link to it. 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. Plase see in for details. hardcode-dll-paths Controls automatic generation of dll-path properties. Allowed values: true, false. 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. Plase see the FAQ entry for details. Note that on Mac OSX, the paths are unconditionally hardcoded by the linker, and it's not possible to disable that behaviour. cflags cxxflags linkflags The value of those features is passed without modification to the corresponding tools. For cflags that's both the C and C++ compilers, for cxxflags that's the C++ compiler and for linkflags that's the linker. The features are handy when you're trying to do something special that cannot be achieved by higher-level feature in Boost.Build. 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. 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 behaviour. The default value is off. 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 to skip building some target in configurations where the build is known to fail.

While Boost.Build V2 is based on the same ideas as Boost.Build V1, some of the syntax was changed, and some new important features were added. This chapter describes most of the changes.

In V1, toolsets were configured by environment variables. If you wanted to use two versions of the same toolset, you had to create a new toolset module that would set the variables and then invoke the base toolset. In V2, toolsets are configured by the using, and you can easily configure several versions of a toolset. See for details.

Probably one of the most important differences in V2 Jamfiles is the use of project requirements. In V1, if several targets had the same requirements (for example, a common #include path), it was necessary to manually write the requirements or use a helper rule or template target. In V2, the common properties can be specified with the requirements project attribute, as documented in . Usage requirements also help to simplify Jamfiles. If a library requires all clients to use specific #include paths or macros when compiling code that depends on the library, that information can be cleanly represented. The difference between lib and dll targets in V1 is completely eliminated in V2. There's only one library target type, lib, which can create either static or shared libraries depending on the value of the <link> feature. If your target should be only built in one way, you can add <link>shared or <link>static to its requirements. The syntax for referring to other targets was changed a bit. While in V1 one would use: exe a : a.cpp <lib>../foo/bar ; the V2 syntax is: exe a : a.cpp ../foo//bar ; Note that you don't need to specify the type of other target, but the last element should be separated from the others by a double slash to indicate that you're referring to target bar in project ../foo, and not to project ../foo/bar.

The command line syntax in V2 is completely different. For example bjam -sTOOLS=msvc -sBUILD=release some_target now becomes: bjam toolset=msvc variant=release some_target or, using implicit features, just: bjam msvc release some_target See the reference for a complete description of the syntax.