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
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.
|Attribute||Name||Default value||Handling by the
|Project id||none||none||Assigned from the first parameter of the 'project' rule. It is assumed to denote absolute project id.|
||The location of jamfile for the project||Sets to the passed value|
||The parent's requirements||The parent's requirements are refined with the passed requirement and the result is used as the project requirements.|
||none||Sets to the passed value|
||Empty if the parent has no build directory set. Otherwise, the parent's build directory with the relative path from parent to the current project appended to it.||Sets to the passed value, interpreted as relative to the project's location.|
Besides defining projects and main targets, Jamfiles often invoke various utility rules. For the full list of rules that can be directly used in Jamfile see the section called “Builtin rules”.
Each subproject inherits attributes, constants and rules
from its parent project, which is defined by the nearest
Jamfile in an ancestor directory above
the subproject. The top-level project is declared in a file
Jamroot rather than
Jamfile. When loading a project,
Boost.Build looks for either
Jamfile. They are handled identically, except
that if the file is called
search for a parent project is not performed.
Even when building in a subproject directory, parent
project files are always loaded before those of their
subprojects, so that every definition made in a parent project
is always available to its children. The loading order of any
other projects is unspecified. Even if one project refers to
another via the
use-project or a target reference,
no specific order should be assumed.
Giving the root project the special name
Jamroot” ensures that
Boost.Build won't misinterpret a directory above it as the
project root just because the directory contains a Jamfile.