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<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
<!ENTITY % scons SYSTEM "../scons.mod">
%scons;
<!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
%builders-mod;
<!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
%functions-mod;
<!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
%tools-mod;
<!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
%variables-mod;
]>
<section id="sect-parseflags"
xmlns="http://www.scons.org/dbxsd/v1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">
<title>Separating Compile Arguments into their Variables: the &ParseFlags; Function</title>
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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 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.
</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>
<scons_example name="parseflags_ex1">
<file name="SConstruct" printme="1">
from __future__ import print_function
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')
</file>
<file name="f1.c">
int main() { return 0; }
</file>
</scons_example>
<scons_output example="parseflags_ex1" os="posix" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
Note that if the options are limited to generic types
like those above,
they will be correctly translated for other platform types:
</para>
<scons_output example="parseflags_ex1" os="win32" suffix="2">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<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>
<scons_example name="parseflags_ex2">
<file name="SConstruct" printme="1">
from __future__ import print_function
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')
</file>
<file name="f1.c">
int main() { return 0; }
</file>
</scons_example>
<scons_output example="parseflags_ex2" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
&ParseFlags; will also accept a (recursive) list of strings as input;
the list is flattened before the strings are processed:
</para>
<scons_example name="parseflags_ex3">
<file name="SConstruct" printme="1">
from __future__ import print_function
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')
</file>
<file name="f1.c">
int main() { return 0; }
</file>
</scons_example>
<scons_output example="parseflags_ex3" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<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>
<scons_example name="parseflags_ex4">
<file name="SConstruct" printme="1">
from __future__ import print_function
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')
</file>
<file name="f1.c">
int main() { return 0; }
</file>
</scons_example>
<scons_output example="parseflags_ex4" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
&ParseFlags; is regularly updated for new options;
consult the man page for details about those currently recognized.
</para>
</section>
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