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 Library
instead of 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 /Fof1.obj /c f1.c /nologo
cl /Fof2.obj /c f2.c /nologo
cl /Fof3.obj /c f3.c /nologo
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 Library call
object files,
and it will correctly realize they are object files.
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 Chapter 5, Node Objects, below, for information about how you can build object files explicitly and include the built files in a library.
The 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 StaticLibrary function
instead of Library:
StaticLibrary('foo', ['f1.c', 'f2.c', 'f3.c'])
There is no functional difference between the
StaticLibrary and Library functions.
If you want to build a shared library (on POSIX systems)
or a DLL file (on Windows systems),
you use the 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 /Fof1.obj /c f1.c /nologo
cl /Fof2.obj /c f2.c /nologo
cl /Fof3.obj /c f3.c /nologo
link /nologo /dll /out:foo.dll /implib:foo.lib f1.obj f2.obj f3.obj
RegServerFunc(target, source, env)
embedManifestDllCheck(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.