The variant_dir
keyword argument of
the SConscript
function provides everything
we need to show how easy it is to create
variant builds using SCons.
Suppose, for example, that we want to
build a program for both Windows and Linux platforms,
but that we want to build it in directory on a network share
with separate side-by-side build directories
for the Windows and Linux versions of the program.
We have to do a little bit of work to construct paths,
to make sure unwanted location dependencies don't creep in.
The top-relative path reference can be useful here.
To avoid writing conditional code based on platform,
we can build the variant_dir
path dynamically:
platform = ARGUMENTS.get('OS', Platform()) include = "#export/$PLATFORM/include" lib = "#export/$PLATFORM/lib" bin = "#export/$PLATFORM/bin" env = Environment( PLATFORM=platform, BINDIR=bin, INCDIR=include, LIBDIR=lib, CPPPATH=[include], LIBPATH=[lib], LIBS='world', ) Export('env') env.SConscript('src/SConscript', variant_dir='build/$PLATFORM')
This SConstruct file, when run on a Linux system, yields:
% scons -Q OS=linux
Install file: "build/linux/world/world.h" as "export/linux/include/world.h"
cc -o build/linux/hello/hello.o -c -Iexport/linux/include build/linux/hello/hello.c
cc -o build/linux/world/world.o -c -Iexport/linux/include build/linux/world/world.c
ar rc build/linux/world/libworld.a build/linux/world/world.o
ranlib build/linux/world/libworld.a
Install file: "build/linux/world/libworld.a" as "export/linux/lib/libworld.a"
cc -o build/linux/hello/hello build/linux/hello/hello.o -Lexport/linux/lib -lworld
Install file: "build/linux/hello/hello" as "export/linux/bin/hello"
The same SConstruct file on Windows would build:
C:\>scons -Q OS=windows
Install file: "build/windows/world/world.h" as "export/windows/include/world.h"
cl /Fobuild\windows\hello\hello.obj /c build\windows\hello\hello.c /nologo /Iexport\windows\include
cl /Fobuild\windows\world\world.obj /c build\windows\world\world.c /nologo /Iexport\windows\include
lib /nologo /OUT:build\windows\world\world.lib build\windows\world\world.obj
Install file: "build/windows/world/world.lib" as "export/windows/lib/world.lib"
link /nologo /OUT:build\windows\hello\hello.exe /LIBPATH:export\windows\lib world.lib build\windows\hello\hello.obj
embedManifestExeCheck(target, source, env)
Install file: "build/windows/hello/hello.exe" as "export/windows/bin/hello.exe"
In order to build several variants at once when using the
variant_dir
argument to SConscript
,
you can call the function repeatedely - this example
does so in a loop. Note that the SConscript
trick of
passing a list of script files, or a list of source directories,
does not work with variant_dir
,
SCons allows only a single SConscript
to be given if
variant_dir
is used.
env = Environment(OS=ARGUMENTS.get('OS')) for os in ['newell', 'post']: SConscript('src/SConscript', variant_dir='build/' + os)