Why does SCons VariantDir() not put output in the given directory?

Question

I'm thinking about using SCons for a new project. It looks really good, though I'm finding VariantDir quite confusing.

I have a simple project with a handful of C source files in one directory, and I want to build in "normal" and in "profile" mode -- with two different sets of options to gcc. I want the outputs to go in the normal/ and profile/ directories, respectively.

For testing, I've cut back to just a single source file, t.c, which has a main() in it. My SConstruct file is in the same directory, and looks like this:

normal = DefaultEnvironment(tools=['mingw'], CCFLAGS = '-O2')
normal.VariantDir('release', '.', duplicate=0)
normal.Program('t', ['t.c'])

#profile = normal.Clone(CCFLAGS='-O2 -pg', LINKFLAGS = '-pg')
#profile.VariantDir('profile', '.', duplicate=0)
#profile.Program('t', ['t.c'])

When I run scons, I'm expecting it to put t.o and t.exe into release/, but it puts them in the current directory. And I can't run it at all with the 3 profile lines uncommented -- if I do, I get this error:

scons: *** Two environments with different actions were specified for the same target: t.o

Basically, I'm unsure why my VariantDir() calls aren't telling scons to put the output in the specified output directory, release.

(I've read a fair bit in the docs and newsgroups, but nothing that answers this question. The closest I've come is this page, which describes a similar thing, but it involves a separate src/ directory and two separate scons files, and importing/exporting variables between them. That doesn't seem pleasant.)

Answer 1

Yes, VariantDir is confusing in scons. Although not well advertised, you can put both SConstruct and SConscript in the same directory, using the current directory as the source directory

# SConstruct
SConscript('SConscript', build_dir='build', src='.')

and

# SConscript
Program('main.c')

I have never found a way to avoid using two files while keeping my sanity trying to understand variant dir :)

Answer 2

I was able to separate binaries in a build directory using this call:

# SConstruct
SConscript('SConscript', variant_dir='build', src_dir='..', duplicate=0)

If you want to put binaries into a directory two levels below, do this:

# SConstruct
SConscript('SConscript', variant_dir='build/release', src_dir='../..', duplicate=0)

Basically, provide the src_dir parameter as a path from your build directory back to your source directory.

Answer 3

As http://www.scons.org/wiki/VariantDir%28%29 said,

Note that when you're not using an SConscript file in the src subdirectory, you must actually specify that the program must be built from the build/hello.c file that SCons will duplicate in the build subdirectory.

VariantDir('release','.',duplicate=0)
env=Environment()
env.Program('release/t',['release/t.c'])

when I run it with scons on Linux.

scons -u . 
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: building associated VariantDir targets: release
gcc -o release/t.o -c t.c
gcc -o release/t release/t.o
scons: done building targets.

I guess it would also work on Win32