Calling a dll from a dll

[phoenix7]

I created a dll named test.dll using c++ with this interface

FunctionBlock* createBlock() ;

Then I wrote a test program to use it and it was successful.

I created another dll named test2.dll with the same way which used test.dll.

But LoadLibrary returned null in when it is called in test2.dll.

Do you have an idea about what the problem is?

[weaknessforcats]

It's a path issue. Have you called SetDllDirectory() before calling
LoadLibrary() ??

LoadLibrary() uses a standard search scheme and if you haven't got the dll path set up you need to hard-code it in the LoadLIbrary() call.

[phoenix7]

Here is my code:

typedef FunctionBlock* (*CreateInstance)();
FunctionBlock* createBlock() 
{
    CreateInstance createInstance;
 
    HINSTANCE hInstLibrary = LoadLibrary(L"C:\\newproject80\\output\\cpp\\FFB2000\\FFB.dll");
 
    if (hInstLibrary)
    {
        DoSomething();
        FreeLibrary(hInstLibrary);
    }
    else
    {
        cout << "DLL Failed To Load!" << std::endl;
    }
}
 

When it is called directly from a console application DoSomething() will be called.
And when it is called inside a dll It outputs "DLL Failed to Load".

I added SetDllDirectory but nothing changed!

[weaknessforcats]

This is the function prototype for LoadLibrary:

HMODULE WINAPI LoadLibrary(
LPCTSTR lpFileName
);

Your call assigns to an HINSTANCE and not an HMODULE.

The arguiment is an LPTCTSR (a long pointer to a const TCHAR string). You have provided:

HINSTANCE hInstLibrary = LoadLibrary(L"C:\\newproject80\\output\\cpp\\FFB20 00\\FFB.dll");

which is a wchar_t string. Not good.

Your code should be:

HMODULE hInstLibrary = LoadLibrary(TEXT("C:\\newproject80\\output\\cpp\\FFB2000\\FFB.dll"));
 

LoadLibrary is a macro that resolves to LoadLibraryA or LoadLibraryW based on the character set (char or wchar_t) used on the build. The TEXT is a TCHAR macro that provides a char string when the build character is char and provodes a wide string when the build character set is multi-byte.

Try this and let me know what happened.

BTW: I hope you are using an _tmain() and all those _t functions.