MSDN

SetLastError function

Namespace: Win32

Sets the last-error code for the calling thread.

Syntax

VOID SetLastError(
    DWORD dwErrCode
);

Parameters

dwErrCode: The error code to be set for the calling thread. Use the GetLastError function to retrieve the error code later.

Return value

This function does not return a value.

Remarks

The error code set by SetLastError is thread‑local; each thread maintains its own last‑error value.
Use GetLastError to retrieve the error code that was set.
Most Windows API functions set the last‑error value on failure, but it should not be used for normal program flow.

Example

#include <windows.h>
#include <stdio.h>

int main(void)
{
    // Force an error
    SetLastError(ERROR_FILE_NOT_FOUND);
    DWORD err = GetLastError();
    printf("Last error: %lu\\n", err);
    return 0;
}

See also