在 /CLR 之下例外狀況處理行為的差異

文章
10/12/2023

使用受控例外狀況的基本概念會討論 Managed 應用程式中的例外狀況處理。在本主題中會詳細討論例外狀況處理之標準行為差異和一些限制。如需詳細資訊，請參閱 _set_se_translator 函式。

跳出最後一個區塊

在原生 C/C++ 程式碼中，雖然它會產生警告，但允許使用結構化例外狀況處理（SEH）跳出 __ finally 區塊。在 /clr 下，跳出 finally 區塊會導致錯誤：

// clr_exception_handling_4.cpp
// compile with: /clr
int main() {
   try {}
   finally {
      return 0;   // also fails with goto, break, continue
    }
}   // C3276

在例外狀況篩選內引發例外狀況

在 Managed 程式碼中處理例外狀況篩選期間引發例外狀況時，會攔截例外狀況，並視為篩選準則傳回 0。

這與引發巢狀例外狀況的原生程式程式碼為相反， 已設定EXCEPTION_RECORD 結構中的 ExceptionRecord 欄位（如 GetExceptionInformation 所傳回），而 ExceptionFlags 欄位會設定0x10位。以下範例說明行為中的差異：

// clr_exception_handling_5.cpp
#include <windows.h>
#include <stdio.h>
#include <assert.h>

#ifndef false
#define false 0
#endif

int *p;

int filter(PEXCEPTION_POINTERS ExceptionPointers) {
   PEXCEPTION_RECORD ExceptionRecord =
                     ExceptionPointers->ExceptionRecord;

   if ((ExceptionRecord->ExceptionFlags & 0x10) == 0) {
      // not a nested exception, throw one
      *p = 0; // throw another AV
   }
   else {
      printf("Caught a nested exception\n");
      return 1;
    }

   assert(false);

   return 0;
}

void f(void) {
   __try {
      *p = 0;   // throw an AV
   }
   __except(filter(GetExceptionInformation())) {
      printf_s("We should execute this handler if "
                 "compiled to native\n");
    }
}

int main() {
   __try {
      f();
   }
   __except(1) {
      printf_s("The handler in main caught the "
               "exception\n");
    }
}

輸出

Caught a nested exception
We should execute this handler if compiled to native

解除關聯重新擲回

/clr 不支援在 catch 處理常式之外重新擲回例外狀況（稱為解除關聯重新擲回）。這個類型的例外狀況會視為標準 C++ 重新擲回。若在發生作用中 Managed 例外狀況時遇到取消關聯重新擲回，例外狀況會包裝為 C ++. 例外狀況，然後重新擲回。此類型的例外狀況只能攔截為類型的 SEHException 例外狀況。

下列範例示範 Managed 例外狀況重新擲回為 C ++. 例外狀況：

// clr_exception_handling_6.cpp
// compile with: /clr
using namespace System;
#include <assert.h>
#include <stdio.h>

void rethrow( void ) {
   // This rethrow is a dissasociated rethrow.
   // The exception would be masked as SEHException.
   throw;
}

int main() {
   try {
      try {
         throw gcnew ApplicationException;
      }
      catch ( ApplicationException^ ) {
         rethrow();
         // If the call to rethrow() is replaced with
         // a throw statement within the catch handler,
         // the rethrow would be a managed rethrow and
         // the exception type would remain
         // System::ApplicationException
      }
   }

    catch ( ApplicationException^ ) {
      assert( false );

      // This will not be executed since the exception
      // will be masked as SEHException.
    }
   catch ( Runtime::InteropServices::SEHException^ ) {
      printf_s("caught an SEH Exception\n" );
    }
}

輸出

caught an SEH Exception

例外狀況篩選和EXCEPTION_CONTINUE_EXECUTION

如果篩選條件在 Managed 應用程式中傳回 EXCEPTION_CONTINUE_EXECUTION，則會視為篩選條件已傳回 EXCEPTION_CONTINUE_SEARCH。如需這些常數的詳細資訊，請參閱 try-except Statement 。

下列範例示範此差異：

// clr_exception_handling_7.cpp
#include <windows.h>
#include <stdio.h>
#include <assert.h>

int main() {
   int Counter = 0;
   __try {
      __try  {
         Counter -= 1;
         RaiseException (0xe0000000|'seh',
                         0, 0, 0);
         Counter -= 2;
      }
      __except (Counter) {
         // Counter is negative,
         // indicating "CONTINUE EXECUTE"
         Counter -= 1;
      }
    }
    __except(1) {
      Counter -= 100;
   }

   printf_s("Counter=%d\n", Counter);
}

輸出

Counter=-3

_set_se_translator函式

由呼叫 _set_se_translator 設定的翻譯工具函式，只影響 Unmanaged 程式碼中的攔截。下列範例示範此限制：

// clr_exception_handling_8.cpp
// compile with: /clr /EHa
#include <iostream>
#include <windows.h>
#include <eh.h>
#pragma warning (disable: 4101)
using namespace std;
using namespace System;

#define MYEXCEPTION_CODE 0xe0000101

class CMyException {
public:
   unsigned int m_ErrorCode;
   EXCEPTION_POINTERS * m_pExp;

   CMyException() : m_ErrorCode( 0 ), m_pExp( NULL ) {}

   CMyException( unsigned int i, EXCEPTION_POINTERS * pExp )
         : m_ErrorCode( i ), m_pExp( pExp ) {}

   CMyException( CMyException& c ) : m_ErrorCode( c.m_ErrorCode ),
                                      m_pExp( c.m_pExp ) {}

   friend ostream& operator <<
                 ( ostream& out, const CMyException& inst ) {
      return out <<  "CMyException[\n" <<
             "Error Code: " << inst.m_ErrorCode <<  "]";
    }
};

#pragma unmanaged
void my_trans_func( unsigned int u, PEXCEPTION_POINTERS pExp ) {
   cout <<  "In my_trans_func.\n";
   throw CMyException( u, pExp );
}

#pragma managed
void managed_func() {
   try  {
      RaiseException( MYEXCEPTION_CODE, 0, 0, 0 );
   }
   catch ( CMyException x ) {}
   catch ( ... ) {
      printf_s("This is invoked since "
               "_set_se_translator is not "
               "supported when /clr is used\n" );
    }
}

#pragma unmanaged
void unmanaged_func() {
   try  {
      RaiseException( MYEXCEPTION_CODE,
                      0, 0, 0 );
   }
   catch ( CMyException x ) {
      printf("Caught an SEH exception with "
             "exception code: %x\n", x.m_ErrorCode );
    }
    catch ( ... ) {}
}

// #pragma managed
int main( int argc, char ** argv ) {
   _set_se_translator( my_trans_func );

   // It does not matter whether the translator function
   // is registered in managed or unmanaged code
   managed_func();
   unmanaged_func();
}

輸出

This is invoked since _set_se_translator is not supported when /clr is used
In my_trans_func.
Caught an SEH exception with exception code: e0000101

另請參閱

例外狀況處理
 safe_cast
MSVC 中的例外狀況處理

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