Linking with a shared library

Introduction

Now we’ve got our application and DLL building as part of the same project, we really ought to persuade them to link together.

The first thing we ought to do is establish some kind of dependency in the code. It’s test-first, but for Jamfiles. We’ll do this by attempting to use one of the symbols exported from the DLL in our MFC application. We’ll add this piece of code to InitInstance:

    int j = fnWin32_dll();

This requires that we include the relevant header file:

#include "win32_dll/win32_dll.h"

It now compiles correctly, but fails to link. We need to establish a dependency on the import library generated as part of the DLL build process. We can add this to the mfc_exe\Jamfile:

LinkLibraries mfc_exe : win32_lib win32_dll ;

This fails because jam doesn’t know how to build win32_dll.lib. We need to add some extra stuff to the SharedLibaryFromObjects rule:

        MakeLocate $(_t) : $(LOCATE_TARGET) ;

        <b># Tell jam where it can find the import library
        MakeLocate $(_t:S=$(SUFLIB)) : $(LOCATE_TARGET) ;</b>

        Clean clean : $(_t) ;

This compiles and links. It even runs – if we make sure that the DLL can be found when loading the EXE.

If we use shared libraries on Unix, we’ll have to invent a SharedLinkLibraries rule, because gcc wants the name of the .so file in order to establish the runtime dependency, and LinkLibraries assumes .lib.

Source code is here.