如何使Qt不省略方法？

Question

I have following Qt project structure:

static library #1

public class LibraryClass
{
     public int Test();
}

static library #2 (reference to library #1)

void SomeMethod()
{
   ...
   x = library1Instance.Test();
   ...
}

executable (reference to library #1 and library #2)

void SomeOtherMethod()
{
   ...
   library2Instance.SomeMethod();
   ...
}

Libraries #1 and library #2 compile without errors. But when I'm trying to compile executable, I got error "undefined reference to LibaryClass::Test()". Which means that libary #1 is linked without LibraryClass::Test() method.

If I create another class in library #1, and make that class reference to LibaryClass::Test() method, everything will compile.

As far as I understood, compiler omits method LibaryClass::Test() because it can found no internal reference to it. So, I should somehow to mark it as method for export or something. How can I do it?

Answer 1

You should make a global definition in a file included in all projects:

#if defined(MAKEDLL)
# define MY_EXPORT Q_DECL_EXPORT
#else
# define MY_EXPORT Q_DECL_IMPORT
#endif

In libraries, add this line to .pro files:

DEFINES   += MAKEDLL

In .pro of executable, add nothing. Then, in library define LibraryClass as

public MY_EXPORT class LibraryClass
{
    ...
}

For static method:

MY_EXPORT void SomeMethod()
{
   ...
   x = library1Instance.Test();
   ...
}

In executable, instantiate the class and call the method as usual. The linker will resolve the dependencies if your subprojects (library1, library2, and executable) are built to the same directory.