Exception specification is not running for me?

Question

4.00/5 (1 vote)

See more:

Hi,

Thanks in advance.
I am trying to restrict exception object data-types from in one of my function. But not able to do it.
As per my understanding, below code should not throw "char" type exception. But still my program is unable to restrict "char" type throw?
I am using visual studio 2008.

Please see the code below:

void FuncThrow(int choice)throw(int, float)
{
switch(choice)
{
case 1: throw 10;
break;
case 2: throw 10.0f;
break;
case 3: throw 'x';
break;
default:
break;
}
}
int main()
{
try
{
FuncThrow(3);
}

catch(int)
{
cout << "Exception from int"<<endl;
}
catch(float)
{
cout << "Exception from float"<<endl;
}
catch(char)
{
cout << "Exception from character"<<endl;
}


}

Posted 14-Jul-11 0:10am

ggupta2009

Updated 14-Jul-11 3:51am

Albert Holguin

v2

Add a Solution

Comments

Richard MacCutchan 14-Jul-11 10:59am

What do you mean by per my understanding, below code should not throw "char" type exception., when that is exactly what your code is doing?

5 solutions

Solution 2

The restriction of the type to be thrown would abuse the structural exception handling. There are no situations where is can be helpful.

—SA

Posted 14-Jul-11 10:10am

Sergey Alexandrovich Kryukov

Comments

Philippe Mori 16-Jul-11 17:16pm

Probably one of the biggest mistake in C++ standard was the exception specification... Complicate for almost no benefits and a few problem like what to do with virtual function... Generally, the base class should not know what exception a derived class would throw.

Another problem is when the code need to be redesigned and a new exception must be thrown, all calling functions must be modified if they themselves have a specification that do not include the new exception. It might even be worst when an application is composed of multiple dynamic libraries (DLL).

In pratice, the only usefull thing to know is that a function would not throw...

Sergey Alexandrovich Kryukov 17-Jul-11 13:09pm

Thank you, Philippe. I agree with your notes.
--SA

Solution 3

See http://msdn.microsoft.com/en-us/library/wfa0edys.aspx[^]

for more information on Visual C++ implementation.

Posted 16-Jul-11 11:50am

Philippe Mori

Solution 4

If you want to simulate exception specification, you can write something like:

void myfunction() throw(int)
try
{
   // Code here
}
catch(int)    // Repeat for each exception in specification
{
    throw;
}
catch(...)
{
    try
    {
        unexpected();
    }
    catch(int)  // Repeat for each exception in specification
    {
    }
    catch(...)
    {
        if (/* std::bad_exception in throw specification */)
            throw std::bad_exception();
        else
            terminate();
    }
}

This would be very similar to what would happen on a conforming compiler...

You can see that for specification with multiple types, the code can rapidly become complex. A compiler might implement that in a more optimal fashion but it does give an idea of what happen under the hood.

Posted 16-Jul-11 12:26pm

Philippe Mori

Comments

Philippe Mori 16-Jul-11 18:31pm

Here I have used a function-try-block. I don't know if it was supported in VS 2008. If not, then you can simply add a pair of { } around the external try-catch block.

Solution 5

An interesting artice on exception specification (why they are evil)

http://www.linuxprogrammingblog.com/cpp-exception-specifications-are-evil[^]

Posted 16-Jul-11 12:34pm

Philippe Mori

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

lewax00 · Accepted Answer · 2011-07-14T04:07:00

Solution 1

Microsoft's compiler doesn't support exception specification except throw().

Source

Posted 14-Jul-11 4:07am

lewax00

Comments

ggupta2009 14-Jul-11 10:50am

Thank you very much...
can you please suggest which would be better alternate to do this?

lewax00 14-Jul-11 11:45am

You can still add them, just make sure you follow them yourself I guess. Or use a different compiler that supports them. I haven't really used them much myself (because I use Visual Studio mostly so there's no point).

Philippe Mori 16-Jul-11 18:04pm

Exception specifications are not really helpful (except maybe an empty throw specification) so the best suggestion is to not uses them.

If you really want, you can simulate the effect by writting a try/catch block and handling exception in a similar way that would happen on a conforming compiler.

Richard MacCutchan 14-Jul-11 10:58am

This is not correct, you can throw any type.

lewax00 14-Jul-11 11:45am

Yes you can throw any type, but Microsoft's compiler does not allow you to restrict which types can be thrown, with the exception of throwing nothing.

Richard MacCutchan 14-Jul-11 11:52am

OK, I misunderstood your comment. Not sure why the OP cares about this.

Sergey Alexandrovich Kryukov 14-Jul-11 16:11pm

I expressed my string opinion in my solution -- please see.
--SA