Out of source build with scons?

Question

I have been using cmake to build my projects out of source, which is really convenient as you avoid polluting your source directory with unnecessary files.

Assuming the CMakeLists.txt is in the current directory, this could be done as follows:

mkdir build
cd build
cmake ..
make

How can I do the same in scons?

Answer 1

In your SConstruct file, you use a variant dir:

SConscript("main.scons", variant_dir="build", duplicate=0)

Then in main.scons you set up everything as usual:

env = Environment()
env.Program(target='foo', source=Split('foo.c bar.c'))

It's possible to do this without hardcoding the variant dir into the SConstruct by (ab)using repositories, but that approach has its bugs. For the record, you would run the above as follows to build in another directory:

mkdir mybuild
cd mybuild
scons -Y .. -f ../main.scons

The easiest and most workable is to just use variant_dir. You then run this as usual from the top level source directory. All the build artefacts get produced in the build sub directory.

In response to JesperE's comment, here is how you could write the top level SConstruct to add an optionally named build directory:

AddOption('--build', default='build')
SConscript("main.scons", variant_dir=GetOption('build'), duplicate=0)

Then you would call this from the command line as follows, to create a build directory called "baz":

$ scons --build=baz

Answer 2

This builds in a subdirectory which is below the root. What if we want the object files, etc to live in a subdirectory below the source? For instance

Top
   - Source
       - Build

instead of

Top
   - Source
   - Build