It's often useful to organize large software projects by collecting parts of the software into one or more libraries. &SCons; makes it easy to create libraries and to use them in the programs.

You build your own libraries by specifying &b-link-Library; instead of &b-link-Program;: Library('foo', ['f1.c', 'f2.c', 'f3.c']) &SCons; uses the appropriate library prefix and suffix for your system. So on POSIX or Linux systems, the above example would build as follows (although &ranlib; may not be called on all systems): % scons -Q cc -o f1.o -c f1.c cc -o f2.o -c f2.c cc -o f3.o -c f3.c ar rc libfoo.a f1.o f2.o f3.o ranlib libfoo.a On a Windows system, a build of the above example would look like: C:\>scons -Q cl /nologo /c f1.c /Fof1.obj cl /nologo /c f2.c /Fof2.obj cl /nologo /c f3.c /Fof3.obj lib /nologo /OUT:foo.lib f1.obj f2.obj f3.obj The rules for the target name of the library are similar to those for programs: if you don't explicitly specify a target library name, &SCons; will deduce one from the name of the first source file specified, and &SCons; will add an appropriate file prefix and suffix if you leave them off.

The previous example shows building a library from a list of source files. You can, however, also give the &b-link-Library; call object files, and it will correctly realize In fact, you can arbitrarily mix source code files and object files in the source list: Library('foo', ['f1.c', 'f2.o', 'f3.c', 'f4.o']) And SCons realizes that only the source code files must be compiled into object files before creating the final library: % scons -Q cc -o f1.o -c f1.c cc -o f3.o -c f3.c ar rc libfoo.a f1.o f2.o f3.o f4.o ranlib libfoo.a Of course, in this example, the object files must already exist for the build to succeed. See , below, for information about how you can build object files explicitly and include the built files in a library.

The &b-link-Library; function builds a traditional static library. If you want to be explicit about the type of library being built, you can use the synonym &b-link-StaticLibrary; function instead of &b-Library;: StaticLibrary('foo', ['f1.c', 'f2.c', 'f3.c']) There is no functional difference between the &b-link-StaticLibrary; and &b-Library; functions.

If you want to build a shared library (on POSIX systems) or a DLL file (on Windows systems), you use the &b-link-SharedLibrary; function: SharedLibrary('foo', ['f1.c', 'f2.c', 'f3.c']) The output on POSIX: % scons -Q cc -o f1.os -c f1.c cc -o f2.os -c f2.c cc -o f3.os -c f3.c cc -o libfoo.so -shared f1.os f2.os f3.os And the output on Windows: C:\>scons -Q cl /nologo /c f1.c /Fof1.obj cl /nologo /c f2.c /Fof2.obj cl /nologo /c f3.c /Fof3.obj link /nologo /dll /out:foo.dll /implib:foo.lib f1.obj f2.obj f3.obj RegServerFunc(target, source, env) Notice again that &SCons; takes care of building the output file correctly, adding the -shared option for a POSIX compilation, and the /dll option on Windows.

Usually, you build a library because you want to link it with one or more programs. You link libraries with a program by specifying the libraries in the &cv-link-LIBS; construction variable, and by specifying the directory in which the library will be found in the &cv-link-LIBPATH; construction variable: Library('foo', ['f1.c', 'f2.c', 'f3.c']) Program('prog.c', LIBS=['foo', 'bar'], LIBPATH='.') Notice, of course, that you don't need to specify a library prefix (like lib) or suffix (like .a or .lib). &SCons; uses the correct prefix or suffix for the current system. On a POSIX or Linux system, a build of the above example would look like: % scons -Q cc -o f1.o -c f1.c cc -o f2.o -c f2.c cc -o f3.o -c f3.c ar rc libfoo.a f1.o f2.o f3.o ranlib libfoo.a cc -o prog.o -c prog.c cc -o prog prog.o -L. -lfoo -lbar On a Windows system, a build of the above example would look like: C:\>scons -Q cl /nologo /c f1.c /Fof1.obj cl /nologo /c f2.c /Fof2.obj cl /nologo /c f3.c /Fof3.obj lib /nologo /OUT:foo.lib f1.obj f2.obj f3.obj cl /nologo /c prog.c /Foprog.obj link /nologo /OUT:prog.exe /LIBPATH:. foo.lib bar.lib prog.obj As usual, notice that &SCons; has taken care of constructing the correct command lines to link with the specified library on each system. Note also that, if you only have a single library to link with, you can specify the library name in single string, instead of a Python list, so that: Program('prog.c', LIBS='foo', LIBPATH='.') is equivalent to: Program('prog.c', LIBS=['foo'], LIBPATH='.') This is similar to the way that &SCons; handles either a string or a list to specify a single source file.

By default, the linker will only look in certain system-defined directories for libraries. &SCons; knows how to look for libraries in directories that you specify with the &cv-link-LIBPATH; construction variable. &cv-LIBPATH; consists of a list of directory names, like so: Program('prog.c', LIBS = 'm', LIBPATH = ['/usr/lib', '/usr/local/lib']) Using a Python list is preferred because it's portable across systems. Alternatively, you could put all of the directory names in a single string, separated by the system-specific path separator character: a colon on POSIX systems: LIBPATH = '/usr/lib:/usr/local/lib' or a semi-colon on Windows systems: LIBPATH = 'C:\\lib;D:\\lib' (Note that Python requires that the backslash separators in a Windows path name be escaped within strings.) When the linker is executed, &SCons; will create appropriate flags so that the linker will look for libraries in the same directories as &SCons;. So on a POSIX or Linux system, a build of the above example would look like: % scons -Q cc -o prog.o -c prog.c cc -o prog prog.o -L/usr/lib -L/usr/local/lib -lm On a Windows system, a build of the above example would look like: C:\>scons -Q cl /nologo /c prog.c /Foprog.obj link /nologo /OUT:prog.exe /LIBPATH:\usr\lib /LIBPATH:\usr\local\lib m.lib prog.obj Note again that &SCons; has taken care of the system-specific details of creating the right command-line options.