Is it possible to use environment variables in a cgo CFLAGS comment?
I'm attempting to write some C bindings for the Go language, and have run into a sort of sticky situation when setting up the Cgo compilation in Windows. I have code that looks like the following:
// #cgo windows CFLAGS: -I C:/dev/extlibs/include/
// #cgo windows LDFLAGS: -lMyLib -L C:/dev/extlibs/lib/
// #include <mylib/mylib.h>
import "C"
which is allows me to avoid installing Dlls, libs, and header files directly into my C:\Windows directory, but doesn't allow for much flexibility when other developers are working with a different file system setup (they all need the libs to be in C:/dev/extlibs/...).
Is there a way I could referent an environment variable from within the code? Perhaps something along the lines of:
// #cgo windows CFLAGS: -I $EXTLIBS$/include/
Or is there another way that people solve this issue that I have missed? I've spent some time googling around on this subject and haven't seen much that has been useful, so any information and/or resources could be a real help!
Answer
According to the docs for CGO:
When building, the CGO_CFLAGS, CGO_CPPFLAGS, CGO_CXXFLAGS and CGO_LDFLAGS environment variables are added to the flags derived from these directives. Package-specific flags should be set using the directives, not the environment variables, so that builds work in unmodified environments.
Using this knowledge, I have had success building a third-party package that wraps a C library so long as it provides it as a system package. The example I linked to:
package sdl
// #cgo LDFLAGS: -lSDL2
// #include <SDL2/SDL.h>
import "C"
Even though it specifies a system package for SDL2, and I have SDL2 installed in some non-system directory, I am able to still build this package using some of the environment variables I mentioned, such as in the following:
export SDL_PATH=/home/mark/where/I/installed/sdl
CGO_CFLAGS="-I$SDL_PATH/include" CGO_LDFLAGS="-L$SDL_PATH/lib" go build hello.go
LD_LIBRARY_PATH="$SDL_PATH/lib" ./hello
Of course, this is Linux, but you can probably use the same ideas in Windows.