division by zero is not caught by catch block?

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Hi consider the following code block

#include<iostream>
int main()
{
    int i=0;
    try{
        int k=9/i;
    }
    catch(...)
    {
     std::cout<<"exception occurs"<<std::endl; //control should come here
    }

}

when I run above code unhandled exception is shown and control doesn't go to catch block
why is it like that?

Posted 7-Jan-14 1:14am

Rahul@puna

Updated 7-Jan-14 1:35am

v2

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uspatel 7-Jan-14 7:25am

Use int k=9/i;

Rahul@puna 7-Jan-14 7:35am

thanks for observing that

3 solutions

Solution 2

It does occur - I just tested it.

C++

int main()
    {
    int i=0;
    try{
        int k=9/i;
        }
    catch(...)
        {
        std::cout<<"exception occurs"<<std::endl; //control should come here
        }
    }

It didn't occur in your original version, because the compiler looked at the code, saw a constant divided by a constant and optimised it to a constant value. And then complained about the divide by zero at compile time instead of run time.

Posted 7-Jan-14 1:42am

OriginalGriff

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Rahul@puna 7-Jan-14 7:52am

@OriginalGriff I have tested the same code as mentioned by you but it stops execution at "int k=9/i" showing unhandled exception while debugging.

Albert Holguin 7-Jan-14 11:22am

Haven't tried it myself... but did you make sure any optimization is turned off in your compiler?

OriginalGriff 7-Jan-14 11:27am

Indeed - a good optimise could remove most of that code!

Albert Holguin 7-Jan-14 11:42am

Yep... and I believe it's on by default in VisualStudio isn't it?

OriginalGriff 7-Jan-14 11:57am

Not for debug code IIRC.
It is for release code.

Rahul@puna 8-Jan-14 0:58am

It's disabled in Visual studio. How does it matter?

OriginalGriff 8-Jan-14 4:24am

It optimisations are turned on, VS looks at your code and makes it work faster, or makes it smaller by moving things around: if your code ends up dividing one constant by another constant for example, VS does it at compile time to save time when it runs. So you won't get a run time "division by zero" error because the divide isn't done at run time.

Solution 3

Division by zero is not a C++ exception so a try-catch block cannot catch it.

Here are some readings for you:
Catching exception: divide by zero[^]
C++ : Catch a divide by zero error[^]

If you're using a VC++ compiler then you can use structured exception handling for this. Here is an example:

C++

#include <windows.h>
#include <Excpt.h>

int main()
{
   int i = 0;
   __try
   {
      int k = 9 / i;
   }
   __except(_exception_code() == EXCEPTION_INT_DIVIDE_BY_ZERO ? EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH)
   {
      std::cout << "exception occurs" << std::endl; //control should come here
   }

   return 0;
}

You can find more examples in MSDN[^].

Posted 7-Jan-14 21:29pm

Marius Bancila

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CPallini · Accepted Answer · 2014-01-07T01:40:00

Solution 1

Beacuse that's not a C++ exception, it is a floating point one, see, for instance, here: "How do I use try…catch to catch floating point errors?"[^].

Posted 7-Jan-14 1:40am

CPallini

Comments

Rahul@puna 7-Jan-14 7:44am

@CPallini catch(...) is for catching any and all types of exceptions thrown from try block.
or it is only for C++ exception as u mentioned.

CPallini 7-Jan-14 7:54am

Quoting linked page: "Some of the confusion here may be over the use of the word "exception". In C++, that's usually referring to the language built-in exception handling system. Floating point exceptions are a different beast altogether"

Stefan_Lang 8-Jan-14 4:10am

+5, very useful link.

This makes me wonder how to control and "catch" other types of system failures such as access violations, stack overflow, etc.. I know how to catch them in the debugger, but I'd much prefer to be able to catch them programmatically in the release version, rather than having the application crash to desktop!

CPallini 8-Jan-14 4:56am

Thank you.