/CLR 下的异常处理行为的差异
使用托管异常中的基本概念 在托管应用程序中讨论异常处理。 在本主题中，从标准行为的不同处理异常和限制一些详细讨论。 有关 SE 转换函数的更多信息，请参见 _set_se_translator。
Finally 块跳出
在本机 C/C++ 代码，跳出finally 块使用结构化异常处理，但允许 (SEH) 将产生警告。在 /clr下，跳出 finally 块产生错误：
// clr_exception_handling_4.cpp
// compile with: /clr
int main() {
try {}
finally {
return 0; // also fails with goto, break, continue
}
} // C3276
引发在异常筛选器中的异常
当一个异常被引发时 异常筛选器 在托管的代码中，异常被捕获并当做筛选器返回了0值。
这与产生嵌入的异常的本机代码的行为是相反的EXCEPTION_RECORD 结构的 ExceptionRecord 字段和 ExceptionFlags 字段返回 (如 GetExceptionInformation) 设置集使用位。 下面的示例中阐释了这种差异。
// 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");
}
}
Output
Caught a nested exception
We should execute this handler if compiled to native
分离的 Rethrows
/clr 不支持在 catch 处理程序外再次引发该异常 (这被称为分离的再次引发。) 此类型异常视为一标准 C++ 异常的再次引发。 如果已分离的再次引发，遇到活动的托管异常时，异常包装为 C.C++ 异常然后再次引发。 此此类型异常只能作为异常System::SEHException被被捕获
以下示例演示托管异常重抛出为C++ 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" );
}
}
Output
caught an SEH Exception
EXCEPTION_CONTINUE_EXECUTION (–1) 异常消除。
如果筛选器在托管应用程序中返回 EXCEPTION_CONTINUE_EXECUTION，它将被视作返回了 EXCEPTION_CONTINUE_SEARCH 有关这些常量的更多信息，请参见 try-except语句。
下面的示例展示了这一主要差异。
// 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);
}
Output
Counter=-3
函数_set_se_translator
转换器函数，通过调用**_set_se_translator**来设置，仅仅会影响非托管代码中的catches。 以下示例展示了这一限制：
// 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();
}
Output
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