# Separating Compile Arguments into their Variables: the &ParseFlags; Function

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

&SCons; &consenvs; have a &f-link-ParseFlags; method that takes a set of typical command-line options and distributes them into the appropriate &consvars; Historically, it was created to support the &f-link-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 &consvars;. Normally, this dictionary would then be passed to &f-link-MergeFlags; to merge the options into a &consenv;, 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")
int main() { return 0; }
scons -Q

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

scons -Q

Since the assumption is that the flags are used for the GCC toolchain, unrecognized flags are placed in &cv-link-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")
void main() { return 0; }
scons -Q

&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")
void main() { return 0; }
scons -Q

If a string begins with a an exclamation mark (`!`), 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")
void main() { return 0; }
scons -Q

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