8.2. Separating Compile Arguments into their Variables: the ParseFlags Function

8.2. Separating Compile Arguments into their Variables: the `ParseFlags` Function
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8.2. Separating Compile Arguments into their Variables: the `ParseFlags` Function

SCons has a bewildering array of construction variables for different types of options when building programs. Sometimes you may not know exactly which variable should be used for a particular option.

SCons construction environments have a ParseFlags method that takes a set of typical command-line options and distributes them into the appropriate construction variables. Historically, it was created to support the ParseConfig method, so it focuses on options used by the GNU Compiler Collection (GCC) for the C and C++ toolchains.

ParseFlags returns a dictionary containing the options distributed into their respective construction variables. Normally, this dictionary would be passed to MergeFlags to merge the options into a construction environment, but the dictionary can be edited if desired to provide additional functionality. (Note that if the flags are not going to be edited, calling MergeFlags with the options directly will avoid an additional step.)

env = Environment()
d = env.ParseFlags("-I/opt/include -L/opt/lib -lfoo")
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')

% scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cc -o f1.o -c -I/opt/include f1.c
cc -o f1 f1.o -L/opt/lib -lfoo

Note that if the options are limited to generic types like those above, they will be correctly translated for other platform types:

C:\>scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cl /Fof1.obj /c f1.c /nologo /I\opt\include
link /nologo /OUT:f1.exe /LIBPATH:\opt\lib foo.lib f1.obj
embedManifestExeCheck(target, source, env)

Since the assumption is that the flags are used for the GCC toolchain, unrecognized flags are placed in $CCFLAGS so they will be used for both C and C++ compiles:

env = Environment()
d = env.ParseFlags("-whatever")
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')

% scons -Q
CCFLAGS -whatever
cc -o f1.o -c -whatever f1.c
cc -o f1 f1.o

ParseFlags will also accept a (recursive) list of strings as input; the list is flattened before the strings are processed:

env = Environment()
d = env.ParseFlags(["-I/opt/include", ["-L/opt/lib", "-lfoo"]])
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')

% scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cc -o f1.o -c -I/opt/include f1.c
cc -o f1 f1.o -L/opt/lib -lfoo

If a string begins with a "!" (an exclamation mark, often called a bang), the string is passed to the shell for execution. The output of the command is then parsed:

env = Environment()
d = env.ParseFlags(["!echo -I/opt/include", "!echo -L/opt/lib", "-lfoo"])
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')

% scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cc -o f1.o -c -I/opt/include f1.c
cc -o f1 f1.o -L/opt/lib -lfoo

ParseFlags is regularly updated for new options; consult the man page for details about those currently recognized.