How to force inclusion of an object file in a static library when linking into executable?
- by Brian Bassett
I have a C++ project that due to its directory structure is set up as a static library A, which is linked into shared library B, which is linked into executable C. (This is a cross-platform project using CMake, so on Windows we get A.lib, B.dll, and C.exe, and on Linux we get libA.a, libB.so, and C.) Library A has an init function (A_init, defined in A/initA.cpp), that is called from library B's init function (B_init, defined in B/initB.cpp), which is called from C's main. Thus, when linking B, A_init (and all symbols defined in initA.cpp) is linked into B (which is our desired behavior).
The problem comes in that the A library also defines a function (Af, defined in A/Afort.f) that is intended to by dynamically loaded (i.e. LoadLibrary/GetProcAddress on Windows and dlopen/dlsym on Linux). Since there are no references to Af from library B, symbols from A/Afort.o are not included into B. On Windows, we can artifically create a reference by using the pragma:
#pragma comment (linker, "/export:_Af")
Since this is a pragma, it only works on Windows (using Visual Studio 2008). To get it working on Linux, we've tried adding the following to A/initA.cpp:
extern void Af(void);
static void (*Af_fp)(void) = &Af;
This does not cause the symbol Af to be included in the final link of B. How can we force the symbol Af to be linked into B?
