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Calling a dynamically loaded DLL is 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.
//From http://www.richelbilderbeek.nl/CppBuilderCallDllDynamic.htm
#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.
Example #1: Without using a struct
//From http://www.richelbilderbeek.nl/CppBuilderCallDllDynamic.htm
#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.
Go back to Richel Bilderbeek's C++ page.
Go back to Richel Bilderbeek's homepage.
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