Question

I am using Visual Studio 10 set to use the v90 platform toolset. I have three applications that use several of the same classes. So, rather than have three copies of each of those classes, I am trying to move them out into a common static lib. One of them is giving me link problems. The others seem to link fine. Here’s the problem class:

HEADER

#ifndef LIMIT_SINGLE_INSTANCE_INCLUDED
#define LIMIT_SINGLE_INSTANCE_INCLUDED

#include <windows.h> 

class CLimitSingleInstance
{
protected:
  DWORD  m_dwLastError;
  HANDLE m_hMutex;

public:
  CLimitSingleInstance(TCHAR *strMutexName);
  ~CLimitSingleInstance();
  BOOL IsAnotherInstanceRunning();
};
#endif

BODY

#include "LimitSingleInstance.h"

CLimitSingleInstance::CLimitSingleInstance(TCHAR *strMutexName)
{
  //Make sure that you use a name that is unique for this application otherwise
  //two apps may think they are the same if they are using same name for
  //3rd parm to CreateMutex
  m_hMutex = CreateMutex(NULL, FALSE, strMutexName); //do early
  m_dwLastError = GetLastError(); //save for use later
}

CLimitSingleInstance::~CLimitSingleInstance() 
{
  if (m_hMutex)  //Do not forget to close handles.
  {
     CloseHandle(m_hMutex); //Do as late as possible.
     m_hMutex = NULL; //Good habit to be in.
  }
}

BOOL CLimitSingleInstance::IsAnotherInstanceRunning() 
{
  return (ERROR_ALREADY_EXISTS == m_dwLastError);
}

When this class is directly part of one of my main application solutions, there is no problem. I have now moved it into my static lib solution, and that solution builds fine. However, I find that I can no longer link my main application solution against my new static lib. Here is the result of attempting to build both debug and release versions of my main application:

—— Rebuild All started: Project: WCCJ, Configuration: ReleaseTENA Win32 —— CAssetEntity.cpp main.cpp ReadWCCJParameters.cpp
WCCJ.cpp WCCJParameters.cpp Generating Code…
DCTUtilsRel.lib(MessageWrapper.obj) : MSIL .netmodule or module
compiled with /GL found; restarting link with /LTCG; add /LTCG to the
link command line to improve linker performance
Creating library ….\bin\WCCJ-TENA.lib and object ….\bin\WCCJ-TENA.exp main.obj : error LNK2001: unresolved external
symbol “public: __thiscall
CLimitSingleInstance::CLimitSingleInstance(char *)”
(??0CLimitSingleInstance@@QAE@PAD@Z) ….\bin\WCCJ-TENA.exe : fatal
error LNK1120: 1 unresolved externals
—— Rebuild All started: Project: WCCJ, Configuration: DebugTENA Win32 —— CAssetEntity.cpp main.cpp ReadWCCJParameters.cpp
WCCJ.cpp WCCJParameters.cpp Generating Code… CAssetEntity.obj :
warning LNK4075: ignoring ‘/EDITANDCONTINUE’ due to ‘/INCREMENTAL:NO’
specification
Creating library ….\bin\WCCJ-TENA-d.lib and object ….\bin\WCCJ-TENA-d.exp main.obj : error LNK2019: unresolved
external symbol “public: __thiscall
CLimitSingleInstance::CLimitSingleInstance(char *)”
(??0CLimitSingleInstance@@QAE@PAD@Z) referenced in function “void
_cdecl `dynamic initializer for ‘gSingleInstanceObj”(void)” (??_EgSingleInstanceObj@@YAXXZ) ….\bin\WCCJ-TENA-d.exe : fatal
error LNK1120: 1 unresolved externals
========== Rebuild All: 0 succeeded, 2 failed, 0 skipped ==========

When I open the .lib in a binary editor and search for the mangled name the linker wants (??0CLimitSingleInstance@@QAE@PAD@Z), I find that it is indeed not found. The closest matches I can find are:

??0CLimitSingleInstance@@QAE@PA_W@Z

??1CLimitSingleInstance@@QAE@XZ

@CLimitSingleInstance@@QAEHXZ

Is anybody able to tell me why this is happening and how to fix it? Thanks in advance.

Dave

Answer 1

The closest matches I can find are: ??0CLimitSingleInstance@@QAE@PA_W@Z

Use the undname.exe utility from the VS command line on that symbol:

C:\>undname ??0CLimitSingleInstance@@QAE@PA_W@Z
Microsoft (R) C++ Name Undecorator
Copyright (C) Microsoft Corporation. All rights reserved.

Undecoration of :- "??0CLimitSingleInstance@@QAE@PA_W@Z"
is :- "public: __thiscall CLimitSingleInstance::CLimitSingleInstance(wchar_t *)"

Note the argument type, wchar_t*, not char*. Your lib project has UNICODE #defined, your exe project does not. The relevant setting is General + Character Set.