How Can I Convert Windows GetLastError() Error Codes into Human-Readable Textual Messages?

Retrieving Textual Error Messages from GetLastError() Error Codes

When performing Windows API calls, the GetLastError() function provides an integer-valued error code indicating any encountered issues. To obtain a more informative error message, follow these steps:

1. Utilize FormatMessageA:

The FormatMessageA function allows you to convert an error code into a textual error message. It requires the following parameters:

• FORMAT_MESSAGE_ALLOCATE_BUFFER: Allocates a buffer to store the message.
• FORMAT_MESSAGE_FROM_SYSTEM: Uses system-supplied error messages.
• FORMAT_MESSAGE_IGNORE_INSERTS: Ignores message modifiers (e.g., "%1").
• NULL: Indicates that the message will be formatted without any parameters.
• &messageBuffer: Pointer to the allocated buffer for the message.

2. Invoke the Function:

Call FormatMessageA with the appropriate parameters, including the error code:

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);

3. Copy and Free the Error Message:

After retrieving the message, copy its contents into a string and free the Win32's allocated buffer:

std::string message(messageBuffer, size);
LocalFree(messageBuffer);

By following these instructions, you can obtain a detailed error message in textual form from the error code returned by GetLastError(), enhancing your understanding of encountered issues during Windows API calls.

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