How to link a C++ shared library with gcc
c, c++, linker, shared-libraries
Solution
Yes, the problem has nothing to do with shared libraries (I think...) and everything to do with name mangling.
In your header, you must declare the function like this:
#ifdef __cplusplus
extern "C" {
#endif
void testfunc(void);
#ifdef __cplusplus
}
#endif
This will cause `testfunc` to have the same symbol and calling conventions for both C and C++.
On the system I'm using right now, the C symbol name will be `_testfunc` and the C++ symbol name (assuming you don't use `extern "C"`) will be `__Z8testfuncv`, which encodes information about the parameter types so overloading will work correctly. For example, `void testfunc(int x)` becomes `__Z8testfunci`, which doesn't collide with `__Z8testfuncv`.
Problem
I have seen a GCC link with a C++ shared library, but I am not able to reproduce it on my own. So first I create a C++ library with a testfunction: ``` g++ -shared -o libtest.so test.c ``` Then I have a test main function which calls the library function and compile it like this ``` gcc -o prog.out main.c -L. -ltest ``` Then i receive the error ``` undefined reference to 'testfunc' ``` which i think is caused by different refernce in the library ... C names the function testfunc and C++ names the function [some stuff]__testfunc[maybe again some stuff]. I have also tried to use ``` gcc -o prog.out main.c -l:libtest.so ``` but this results in the same error. Therefore, my question is: How is it possible to link a c++ library with gcc to a c file? Update: I know i can use `extern "C"`, but that's not the way it is solved. Maybe there are some parameters for the linker instead? Update2: Just thought it could also be possible that the first part is just compiled with c++ and linked with gcc. Also tried this: ``` g++ -c testlib.c -o testlib.o gcc -shared -o libtest.so testlib.o gcc -o prog.out -l:libtest.so ``` still doesn't work. Is there something wrong with the flags?