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<para>
&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.
</para>
<para>
&SCons; construction environments have a &ParseFlags; method
that takes a set of typical command-line options
and distrbutes 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.
</para>
<para>
&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 &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.)
</para>
<programlisting>
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')
</programlisting>
<screen>
% <userinput>scons -Q</userinput>
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
</screen>
<para>
Note that if the options are limited to generic types
like those above,
they will be correctly translated for other platform types:
</para>
<screen>
C:\><userinput>scons -Q</userinput>
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
</screen>
<para>
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:
</para>
<programlisting>
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')
</programlisting>
<screen>
% <userinput>scons -Q</userinput>
CCFLAGS -whatever
cc -o f1.o -c -whatever f1.c
cc -o f1 f1.o
</screen>
<para>
&ParseFlags; will also accept a (recursive) list of strings as input;
the list is flattened before the strings are processed:
</para>
<programlisting>
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')
</programlisting>
<screen>
% <userinput>scons -Q</userinput>
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
</screen>
<para>
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:
</para>
<programlisting>
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')
</programlisting>
<screen>
% <userinput>scons -Q</userinput>
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
</screen>
<para>
&ParseFlags; is regularly updated for new options;
consult the man page for details about those currently recognized.
</para>
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