MS Visual Studio 2010: _UzpVersion is requested by object file, but _UzpVersion@0 is exported by library

Question

I'm trying to build my project using MS Visual Studio 2010 with the Info-ZIP unzip library. When I inserted UzpVersion() call into the code, the linker failed saying:

error LNK2019: unresolved external symbol _UzpVersion referenced in function _wmain

DUMPBIN shows that the library exports _UzpVersion@0 (it was compiled with the same compiler). But the object file requests _UzpVersion. The function is declared as:

extern "C" {

const UzpVer * UzpVersion(void);

}

What is wrong with it? How to fix it? Sorry, I'm not proficient with Visual C++; I spent most of my time with GNU C++.

Answer 1

Figured it out by myself.

The library is compiled with __stdcall calling convention, but does not declare exported functions as such. Visual Studio 2010 by default compiles a project with /Gd flag, that switches to __cdecl calling convention. Besides other, these calling conventions are also using different name mangling schemes for C functions.

You can read details on MSDN.

For Info-ZIP library in particular, the issue is fixed by adding the following defines before including the unzip.h header:

#define EXPENTRY __stdcall
#define USE_UNZIP_LIB

Answer 2

This is a linkage error. The compiler see's the declaration of UzpVersion, otherwise, it would have failed to compile. You need to make sure you've configured your project to include the .lib.

EDIT: Additionally, you said you're compiling it yourself. Make sure you're compiling the sources as C and not C++.