VC++ exception handling - app crashes anyway

Question

Following is the code snippet I have written in the process of learning exception handling in C++(using visual studio 2010 compiler).

#include "stdafx.h" #include <iostream> using namespace std; void multi_double() { double first,second,product; try{ cout << "Enter the first number\n"; cin >> first; cout << "Enter the second number\n"; cin >> second; product = first * second; cout << product; } catch(...){cout << "Got an exceptional behaviour";} } void stud_age(){ int age; try{ cout << "Enter student's age\n"; cin >> age; if(age < 0) throw; cout << endl <<age; } catch(...) { cout << "Caught here\n"; } } class Model{ public: Model(){cout << "ctor\n";} ~Model(){cout << "dtor\n";} }; int _tmain(int argc, _TCHAR* argv[]) { //multi_double(); //stud_age(); int a; try{ Model obj; int *p = NULL; *p = 0;//expecting access violation exception } catch(...){ cout << "caught an exception\n"; } return 0; }

Enable C++ exception is set to Yes[/EHsc]. But when I run the application,it is still crashing anyway ! with following information:

Problem signature: Problem Event Name: APPCRASH Application Name: DataTypeConversions.exe Application Version: 0.0.0.0 Application Timestamp: 4ffd8c3d Fault Module Name: DataTypeConversions.exe Fault Module Version: 0.0.0.0 Fault Module Timestamp: 4ffd8c3d Exception Code: c0000005 Exception Offset: 00001051

Why is not control coming to catch block?!

You need to compile with /EHa to have catch(...) also catch processor exceptions. Which is a Really Bad Idea. — Hans Passant
– Hans Passant, Commented Jul 11, 2012 at 15:30

Nordic Mainframe · Accepted Answer · 2012-07-11 14:53:42Z

Access Violations and all other kinds of hardware exceptions are handled in Windows using a mechanism called "C Structured Exception Handling (SEH)". This was originally designed to give C programs a more "structured" way to handle exceptions than the usual signal()/sigaction() mechanism in Posix based systems.

SEH exceptions can be integrated into the C++ Exception system, by setting a translator function which is called before SEH stack unwinding takes place. The new translator function simply throws a C++ exception and, presto, C++ can catch the error!

See this Document from the MSDN for all the details:

http://msdn.microsoft.com/de-de/library/5z4bw5h5(v=vs.80).aspx

And here's a working example:

#include <windows.h> #include <iostream> #include <eh.h> // You need to enable the /EHa excpetion model to make this work. // Go to // Project|Properties|C/C++|Code Generation|Enable C++ Exceptions // and select "Yes with SEH Exceptions (/EHa)" void trans_func( unsigned int u, EXCEPTION_POINTERS* pExp ) { // printf( "In trans_func.\n" ); throw "Hardware exception encountered"; } int main() { _set_se_translator(trans_func); try { int *p = NULL; *p = 0;//expecting access violation exception } catch(const char *s) { std::cout << "caught an exception:" << s << "\n"; } return 0; }

Hampus Nilsson · Accepted Answer · 2012-07-11 14:28:36Z

The C++ exception handling system can not hardware-generated (ie. access violation etc) exceptions, only exceptions generated by code through throw exception;.

If you want to catch these exceptions, it is only possible in Windows through the use of structured exceptions. This is not compatible with other compilers and uses the __try __except construct rather than normal try / catch.

SEH exceptions and C++ exceptions can be fused together, see my answer.

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