This is a somewhat abstract example of one way in which you can use Jam to build a project whose sources are spread over several subdirectories.

In this example, we introduce the "Jamrules" file, which generally contains site or project specific configuration, rules, and actions. In this case, the Jamrules only sets the ALL_LOCATE_TARGET variable, which specifies where to put generated files.

We also demonstrate the use of the SubDir and SubInclude rules to compile the contents of sub directories.

Note that there's a Jamfile for each directory in which sources reside. Each contains only a call to the Library rule specifying that a library should be made from the source files in that directory. The Jamfiles in the sub directories could of course be arbitrarily complex, but it is usually best to keep them as simple as possible.

Things to try:

• Run jam, then touch or edit one of the header files - for example, "b.h" in the "b" directory. Notice that jam knew which source files #included "b.h" (see the section called "Header File Processing" in the Jamfiles and Jambase document for information on how this works). Then try making one header file #include another, and touch the #included file. Jam understands the new relationship, without the need for a "make depends", and it does it fast.
• Do a "jam clean" from the top directory, and then try running jam from within one of the source sub directories. Note that (with this particular setup) Jam will only compile the library corresponding to that particular sub directory. This sort of arrangement can be helpful in modularizing large and/or multi-platform projects.
• Try adding your own call to "InstallBin" in the top level Jamfile (see the simple example for an example of using InstallBin). Then, hypothesize that for this project you actually want to install one or more of the libraries, and add a call to "InstallLib" to tell jam which libraries to install and where. (Hint: on a "real" project, the directory into which things are installed would probably be specified one way or another in the Jamrules. Try setting a variable containing your install path in the Jamrules and then pass that variable to the appropriate install rule.) See the Jamfiles and Jambase file for more information on InstallLib and other rules.