CODEWITHSUNDEEP
cwindowsdll
IGP
IGP

Reputation: 67

Why does GetLastError return ERROR_INVALID_HANDLE?

I have trouble understanding what happens to the getlasterror function in the below code.
My dll is a valid one and LoadLibrary and FreeLibrary do not fail, but GetLastError returns:

6 (ERROR_INVALID_HANDLE).

The code:

int main()
{
    const char* mydll = "mydll.dll";
    HINSTANCE hinstLib;


    hinstLib = LoadLibraryA(mydll);

    if (hinstLib) {

        int rez = FreeLibrary(hinstLib);
        
        if (rez) {
            printf(" SUCCESS but Geterror:: %d\n", GetLastError());
        }
    }

    return 0;
}

Upvotes: 1

Views: 472

Answers (1)

Adrian Mole
Adrian Mole

Reputation: 51894

There is nothing in the documentation for FreeLibrary() indicating (or even suggesting) that the calling thread's error code will be set on a successful call. Thus, your call to GetLastError() following a non-zero (successful) return from FreeLibrary() would seem to be returning an 'arbitrary' value.

From the GetLastError() documentation:

The Return Value section of the documentation for each function that sets the last-error code notes the conditions under which the function sets the last-error code. Most functions that set the thread's last-error code set it when they fail. However, some functions also set the last-error code when they succeed. If the function is not documented to set the last-error code, the value returned by this function is simply the most recent last-error code to have been set; some functions set the last-error code to 0 on success and others do not.

You could probably verify this by explicitly setting your thread's error code before calling FreeLibrary():

    //...
    SetLastError(0); // Set last error code
    int rez = FreeLibrary(hinstLib);
    //...

EDIT: If, even with this in place, you are still seeing a 'consistent' value for the last error, then it is likely that your mydll.dll is itself calling a WinAPI function that fails (with the reason/error being INVALID_HANDLE_VALUE), from code executed in the DLL_PROCESS_DETACH section of its DllMain() procedure. However, if that procedure still returns TRUE, then the FreeLibrary() function will also return TRUE(i.e. it will signal that your DLL was unloaded).

Upvotes: 2

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