How to Translate Windows API Error Codes into Human-Readable Error Messages?

Retrieving Error Messages from Error Codes: Demystifying GetLastError()

Question:

After invoking Windows API functions, how can we access the corresponding error message in a comprehensible textual format? GetLastError() merely provides numeric error codes.

Answer:

To convert the numerical error code reported by GetLastError() into a meaningful string representation, we employ the following steps:

//Returns the last Win32 error, in string format. Returns an empty string if there is no error.
std::string GetLastErrorAsString()
{
    //Fetch the error message ID (if any)
    DWORD errorMessageID = ::GetLastError();
    if (errorMessageID == 0) {
        return std::string(); //No error message recorded
    }

    LPSTR messageBuffer = nullptr;

    //Request Win32 to translate the error ID into a string representation
    //We specify options to allocate the message buffer dynamically and retrieve the localized system message
    size_t size = FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
                                 NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&messageBuffer, 0, NULL);

    //Copy the error message into a string
    std::string message(messageBuffer, size);

    //Release the dynamically allocated buffer used by Win32
    LocalFree(messageBuffer);

    return message;
}

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