Xcode iOS Project Fails When I Add C++ Code

Question

I have an OpenGL Xcode project, but when I want to add a .h and a .cpp file, it doesn't compile, even if I tell not to compile those files.

I get this error:

Apple Mach-O linker error

Undefined symbols for architecture i386:
  "_read_png_image", referenced from:
  read_png_texture(char const*, bool) in TextureUtilities.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

The underlying cause of the error is that read_png_image() is a C function, but has been compiled with C++ linkage - which results in a 'mangled' symbol name that includes information about the types of the function's arguments.

The solution is to wrap the declaration of the function with extern "C" :

extern "C"
{
    void read_png_image(char const*, bool);
} 

Presumably the .cpp file you added includes the declaration - possibly form a pre-compiled header.