linker - How to dllimport in Microsoft Visual C++

Question

I have a DLL and I would like to use some of its functions.

#include <iostream>

using namespace std;

extern "C" __declspec(dllimport) int Initialize(char* localPort, char* adminServerName, int rpcTimeout);


int main()
{
    int res = Initialize("7864", "6000@kabc", 10000);

    return 0;
}

I don't have the DLL's .lib file, so is there anyway I can link to it. One thing that comes to my mind is to use the LoadLibrary function and then use the GetProcAddress(). Is there any other way?

When I compile the following code

• error LNK2019: unresolved external symbol _imp_Initialize referenced in function _main

• fatal error LNK1120: 1 unresolved externals

I get the above errors

I'm using Windows and Visual Studio 2008

Answer 1

From your phrasing it is pretty clear you are using Dev Studio some or other version.

In order to implicitly link against a dll, VC++ needs a .lib file, no questions. Without a .lib you can only explicitly load the dll using LoadLibrary and GetProcAddress.

Fortunately import libraries contain nothing other than the dll's exported symbols, so it is perfectly legitimate to simply create a dll project in VC++ that exports the identical symbols, build it, and then use the resulting .lib file to access the target dll.

The trick really is, getting the symbols right: Depending on how the original dll was created there might be some decoration to deal with.

"Initialize" could be exported from a dll in several ways when viewed with dependencywalker

• "Initialize" - was either exported via a .DEF file, or via extern "C" __declspec(dllexport) int __cdecl Initialize(...
• "_Initalize@16" - was exported using: extern "C" __declspec(dllexport) int __stdcall Initialize(...
• ?Initialize@@YAHPADOH@Z" - `__declspec(dllexport) int Initialize(char*,char*,int);
• ?Initialize@@YGHPADOH@Z" - `__declspec(dllexport) int __stdcall Initialize(char*,char*,int);

The problem really is the first case - if the calling convention isn't __cdecl (and most dll api's are actually __stdcall - all windows dlls are __stdcall) then you must use a .def file to export the undecorated names.