Retrieving the Last-Error Code

When many system functions fail, they set the last-error code. If your application needs more details about an error, it can retrieve the last-error code using theGetLastError function and display a description of the error using theFormatMessage function.

The following example includes an error-handling function that prints the error message and terminates the process. ThelpszFunction parameter is the name of the function that set the last-error code.

#include <windows.h>#include <strsafe.h>void ErrorExit(LPTSTR lpszFunction) {     // Retrieve the system error message for the last-error code    LPVOID lpMsgBuf;    LPVOID lpDisplayBuf;    DWORD dw = GetLastError();     FormatMessage(        FORMAT_MESSAGE_ALLOCATE_BUFFER |         FORMAT_MESSAGE_FROM_SYSTEM |        FORMAT_MESSAGE_IGNORE_INSERTS,        NULL,        dw,        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),        (LPTSTR) &lpMsgBuf,        0, NULL );    // Display the error message and exit the process    lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT,         (lstrlen((LPCTSTR)lpMsgBuf) + lstrlen((LPCTSTR)lpszFunction) + 40) * sizeof(TCHAR));     StringCchPrintf((LPTSTR)lpDisplayBuf,         LocalSize(lpDisplayBuf) / sizeof(TCHAR),        TEXT("%s failed with error %d: %s"),         lpszFunction, dw, lpMsgBuf);     MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK);     LocalFree(lpMsgBuf);    LocalFree(lpDisplayBuf);    ExitProcess(dw); }void main(){    // Generate an error    if(!GetProcessId(NULL))        ErrorExit(TEXT("GetProcessId"));}