-clr 下的异常处理行为区别

项目
10/19/2023

使用托管异常的基本概念讨论托管应用程序中的异常处理。本主题中详细讨论了异常处理的标准行为中的差异以及某些限制。有关详细信息，请参阅 _set_se_translator 函数。

跳出 Finally 块

在本机 C/C++ 代码中，允许使用结构化异常处理 (SEH) 跳出 __finally 块，但将产生警告。在 /clr 下，跳出 finally 块将导致错误：

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

引发异常筛选器中的异常

在托管代码中的异常筛选器处理过程中引发异常时，将会捕获异常并将其按照筛选器返回 0 来对待。

这与本机代码中的行为是相反的：将引发嵌套异常，设置 EXCEPTION_RECORD 结构中的 ExceptionRecord 字段（由 GetExceptionInformation 返回），并且 ExceptionFlags 字段将设置 0x10 位。以下示例阐释了这种行为差异：

// 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");
    }
}

输出

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

解除关联的重新引发

/clr 不支持在 catch 处理程序外部重新引发异常（这称为“解除关联的重新引发”）。此类型的异常被视为一个标准的 C++ 重新引发。如果在存在活动的托管异常时遇到解除关联的重新引发，则此异常将包装为 C++ 异常，然后重新引发。此类型的异常只能作为 SEHException 类型的异常被捕获。

以下示例演示了作为 C++ 异常重新引发的托管异常：

// 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" );
    }
}

输出

caught an SEH Exception

异常筛选器和 EXCEPTION_CONTINUE_EXECUTION

如果筛选器在托管应用程序中返回 EXCEPTION_CONTINUE_EXECUTION，则将按照筛选器返回 EXCEPTION_CONTINUE_SEARCH 对其进行处理。有关这些常量的详细信息，请参阅 try-except 语句。

以下示例演示了这一差异：

// 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);
}

输出

Counter=-3

_set_se_translator 函数

通过调用 _set_se_translator 设置的转换器函数仅会影响非托管代码中的 catch 语句。以下示例演示了这一限制：

// 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();
}

输出

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

另请参阅

异常处理
 safe_cast
MSVC 中的异常处理

通过