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(C++ Builder) Call a dynamically loaded DLL

One of the two ways to call a DLL, the other way is to call a statically loaded DLL.

In the two equivalent examples below, the function GetAnswerOfLife is called from the file ProjectDll.DLL and its answer (which should be 42) is checked.

Example #0: Using a struct

My favorite and more exception safe solution.

#include <windows.h>

struct DllHandle

{

DllHandle(const char * const filename)

: h(LoadLibrary(filename)) {}

~DllHandle() { if (h) FreeLibrary(h); }

const HINSTANCE Get() const { return h; }

private:

HINSTANCE h;

};

int main()

{

//Obtain a handle to the DLL

const DllHandle h("ProjectDll.DLL");

if (!h.Get())

{

MessageBox(0,"Could not load DLL","UnitCallDll",MB_OK);

return 1;

}

//Obtain a handle to the GetAnswerOfLife function

typedef const int (*GetAnswerOfLifeFunction)();

const GetAnswerOfLifeFunction AnswerOfLife

= reinterpret_cast<GetAnswerOfLifeFunction>(

GetProcAddress(h.Get(),"_GetAnswerOfLife"));

if (!AnswerOfLife) //No handle obtained

{

MessageBox(0,"Loading AnswerOfLife failed","UnitCallDll",MB_OK);

return 1;

}

if (AnswerOfLife() != 42)

{

MessageBox(0,"Function AnswerOfLife failed","UnitCallDll",MB_OK);

return 1;

}

else

{

MessageBox(0,"Function AnswerOfLife successful!","UnitCallDll",MB_OK);

}

}

When you look at the GetProcAddress function, you'll note that C++ Builder add a leading underscore in the function name.

*        View this code in plain text.

*        Download the project with this example (zip).

Example #1: Without using a struct

#include <windows.h>

int main()

{

//Obtain a handle to the DLL

const HINSTANCE dllHandle = LoadLibrary("ProjectDll.DLL");

if (!dllHandle)

{

MessageBox(0,"Could not load DLL","UnitCallDll",MB_OK);

return 1;

}

//Obtain a handle to the GetAnswerOfLife function

typedef const int (*GetAnswerOfLifeFunction)();

const GetAnswerOfLifeFunction AnswerOfLife

= reinterpret_cast<GetAnswerOfLifeFunction>(

GetProcAddress(dllHandle,"_GetAnswerOfLife"));

if (!AnswerOfLife) //No handle obtained

{

MessageBox(0,"Loading AnswerOfLife failed","UnitCallDll",MB_OK);

FreeLibrary(dllHandle);

return 1;

}

if (AnswerOfLife() != 42)

{

MessageBox(0,"Function AnswerOfLife failed","UnitCallDll",MB_OK);

FreeLibrary(dllHandle);

return 1;

}

else

{

MessageBox(0,"Function AnswerOfLife successful!","UnitCallDll",MB_OK);

FreeLibrary(dllHandle);

}

}

When you look at the GetProcAddress function, you'll note that C++ Builder add a leading underscore in the function name.

*        View this code in plain text.

*        Download the project with this example (zip).

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.