Unresolved external symbol when lib is linked, compiler adds the letter 'A' to the function name

Question

I get this error when trying to link a win32 exe project. I have linked in the lib that contains the code for this method. But still gets an unresolved symbol error.

error LNK2001: unresolved external symbol "public: bool __thiscall SharedJobQueue::AddJobA(class boost::shared_ptr<class domain::Job>)" (?AddJobA@SharedJobQueue@@QAE_NV?$shared_ptr@VJob@domain@@@boost@@@Z)

Why does it say AddJobA with the 'A' at the end. The method is declared as AddJob.

I have looked in the output from 'dumpbin /symbols' and it only contains symbols for AddJob not AddJobA. Why do the compiler add an 'A' to the end of the function name?

Answer 1

Windows functions may have A or W at the end of a function -- A signifies ASCII and W signifies a Wide fixed size unicode. Your project settings determine which function is used. addJob could have had W at the end if you had unicode enabled for your project..

Answer 2

MS uses macros for the Win32 API to support both Unicode and Ansi builds by suffixing the function names with A or W.
AddJob() is a function in the Win32 API and thus has such a macro - you can #undef AddJob to get rid of your problem.

Answer 3

And here we see the problem with macros.

There is nothing wrong with your code per se, the problem is with the windows libraries. There is actually a function called AddJob in the Win32 headers, but not quite... The don't declare an Addjob function, but instead an AddJobA and an AddJobW function, which deal with non-unicode and unicode strings respectively.

The A at the end of your function name is due to a macro defined in the windows header that was defined to deal with unicode. Essentially they'll have something like:

#ifdef UNICODE
#  define AddJob AddJobW
#else
#  define AddJob AddJobA
#endif

This allows people to just use AddJob and the macros will point the function towards the correct unicode/non-unicode function. The problem of course is that the #define affects everything, which is what's happening to your function.

To fix this, you can either #undef AddJob or simply change the name of your function to something that isn't a Win32 function.