Hantering av fel (Windows Internet)

Funktionen GetLastError hämtar den sista felkoden för alla WinINet-funktioner. Om ERROR_INTERNET_EXTENDED_ERROR returneras finns det en sträng eller buffert som innehåller ett detaljerat felmeddelande. Anropa funktionen InternetGetLastResponseInfo för att hämta den utökade feltexten.

För att få feltexten för ett fel anropar du funktionen FormatMessage och skickar den ett HMODULE- handtag till Wininet.dll, som kan hämtas med hjälp av funktionen GetModuleHandle.

Följande är ett exempel på en funktion för felhantering.

#include <windows.h>
#include "strsafe.h"
#include "wininet.h"
#include <stdlib.h>
#pragma comment(lib, "wininet.lib")
#pragma comment(lib, "user32.lib")

#define  INET_ERR_OUT_MSG_BOX_BUFFER_SIZE      512
#define  INET_ERR_OUT_FORMAT_BUFFER_SIZE       256

#ifdef  _UNICODE
#define _itot _itow_s
#else
#define _itot _itoa_s
#endif

// Forward declaration of helper function
void WINAPI addLastErrorToMsg( LPTSTR szMsgBuffer, DWORD dwSize );

// Function for displaying Internet Error information in a message box
BOOL WINAPI InternetErrorOut(
                              HWND hWnd,
                              DWORD dwError,
                              LPCTSTR szFailingFunctionName )
{
  HANDLE hProcHeap;
  TCHAR  szMsgBoxBuffer[INET_ERR_OUT_MSG_BOX_BUFFER_SIZE],
         szFormatBuffer[INET_ERR_OUT_FORMAT_BUFFER_SIZE],
         szConnectiveText[]  = { TEXT( "\nAdditional Information: " )},
        *szExtErrMsg         = NULL,
        *szCombinedErrMsg    = NULL;
  DWORD  dwInetError,
         dwBaseLength,
         dwExtLength = 0;

  if( ( hProcHeap = GetProcessHeap( ) ) == NULL )
  {
    StringCchCopy( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
      TEXT( "Call to GetProcessHeap( ) failed..." ) ); 
    goto InetErrorOutError_1;
  }

  dwBaseLength = FormatMessage(
    FORMAT_MESSAGE_FROM_HMODULE,             // dwFlags
    GetModuleHandle( TEXT("wininet.dll") ),  // lpSource
    dwError,                                 // dwMessageId
    0,                                       // dwLanguageId
    (LPTSTR)szFormatBuffer,                  // lpBuffer
    INET_ERR_OUT_FORMAT_BUFFER_SIZE,         // nSize
    NULL );                                  // * arguments

  if( !dwBaseLength )
  {
    StringCchCopy( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
                   TEXT( "Call to FormatMessage( ) failed..." ) ); 
    addLastErrorToMsg( szMsgBoxBuffer, 
                       INET_ERR_OUT_MSG_BOX_BUFFER_SIZE );
    goto InetErrorOutError_1;
  }

  if( FAILED( StringCchPrintf( szMsgBoxBuffer, 
                INET_ERR_OUT_MSG_BOX_BUFFER_SIZE,
                TEXT( "%s error; code: %d\nDescription: %s\n" ),
                szFailingFunctionName, dwError, szFormatBuffer ) ) )
  {
    StringCchCopy( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
      TEXT( "Call to StringCchPrintf( ) failed...\n" ) ); 
    goto InetErrorOutError_1;
  }

  StringCchLength( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE,
                (size_t*) &dwBaseLength );
  // Adjust base-length value to count the number of bytes:
  dwBaseLength *= sizeof( TCHAR );

  if( dwError == ERROR_INTERNET_EXTENDED_ERROR )
  {
    InternetGetLastResponseInfo( &dwInetError, NULL, &dwExtLength );
    // Adjust the extended-length value to a byte count 
    // that includes the terminating null:
    ++dwExtLength *= sizeof( TCHAR );
    if( ( szExtErrMsg = (TCHAR*)HeapAlloc( hProcHeap, 0, dwExtLength)) 
         == NULL )
    {
      StringCchCat( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
        TEXT("\nFailure: Could not allocate buffer for addional details.")); 
      addLastErrorToMsg( szMsgBoxBuffer, 
                         INET_ERR_OUT_MSG_BOX_BUFFER_SIZE );
      goto InetErrorOutError_1;
    }

    if( !InternetGetLastResponseInfo( &dwInetError, 
                                      szExtErrMsg, 
                                      &dwExtLength ) )
    {
      StringCchCat( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
        TEXT( "\nCall to InternetGetLastResponseInfo( ) failed--" ) ); 
      addLastErrorToMsg( szMsgBoxBuffer, 
                         INET_ERR_OUT_MSG_BOX_BUFFER_SIZE );
      goto InetErrorOutError_2;
    }
    dwBaseLength += dwExtLength + sizeof( szConnectiveText );
  }

  if( ( szCombinedErrMsg = (TCHAR*)HeapAlloc( hProcHeap, 0, 
                                              dwBaseLength + sizeof(TCHAR) ) ) 
                         == NULL )
  {
    StringCchCat( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
      TEXT( "\nFailure: Could not allocate final output buffer." ) ); 
    addLastErrorToMsg( szMsgBoxBuffer, 
                       INET_ERR_OUT_MSG_BOX_BUFFER_SIZE );
    goto InetErrorOutError_2;
  }

  if( FAILED( StringCchCopy( szCombinedErrMsg, 
                dwBaseLength, szMsgBoxBuffer ) ) ||
      ( dwExtLength && 
        ( FAILED( StringCchCat( szCombinedErrMsg, 
                    dwBaseLength, szConnectiveText ) ) ||
          FAILED( StringCchCat( szCombinedErrMsg, 
                    dwBaseLength, szExtErrMsg ) ) ) ) )
  {
    StringCchCat( szMsgBoxBuffer, INET_ERR_OUT_MSG_BOX_BUFFER_SIZE, 
      TEXT( "\nFailure: Could not assemble final message." ) ); 
    goto InetErrorOutError_3;
  }

  MessageBox( hWnd, 
    szCombinedErrMsg, 
    TEXT( "Internet Error Message" ),
    MB_OK | MB_ICONERROR );
  HeapFree( hProcHeap, 0, szExtErrMsg );
  HeapFree( hProcHeap, 0, szCombinedErrMsg );

  return( TRUE );

InetErrorOutError_3:
  HeapFree( hProcHeap, 0, szCombinedErrMsg );
InetErrorOutError_2:
  HeapFree( hProcHeap, 0, szExtErrMsg );
InetErrorOutError_1:
  MessageBox( hWnd,
    (LPCTSTR) szMsgBoxBuffer,
    TEXT( "InternetErrorOut( ) Failed" ),
    MB_OK | MB_ICONERROR );
  return( FALSE );
}


void WINAPI addLastErrorToMsg( LPTSTR szMsgBuffer, DWORD dwSize )
{
  TCHAR szNumberBuffer[32];

  _itot( GetLastError( ), szNumberBuffer, 10 );
  StringCchCat( szMsgBuffer, dwSize, 
        TEXT( "\n   System Error number: " ) ); 
  StringCchCat( szMsgBuffer, dwSize, szNumberBuffer );
  StringCchCat( szMsgBuffer, dwSize, TEXT( ".\n" ) ); 
}