newbie..Exception Handling

[udit99]

here's a code I gleaned frrom a book...

#include<iostream.h>

class Bummer{};
class Dummer{};
class Dumm{};
void main()
{
try{

throw Dumm();
}
catch(Bummer)
{
cout<<"helo Bumer";
}
catch(Dummer)
{
cout<<"helo Dummer";
}
catch(...)
{
cout<<"helo rest of u";
}

}


what I wanna know is tt y is it necessary 2 create these Classes ..Bummer Dummer..I mean..y cant v just say sumthing lik

throw(5)

catch(int i)
{
select case i
{
//coding here...
}

[kedaman]

It's not nessesary, you can use it for simple error codes, but if you want to have an error container that stores additional data about what happened, say if you have an error class filenotfound, then you can store it's filename and in the catch you display the filename that wasn't found.

[parksie]

Anything can be thrown, but the best thing to throw is a class derived from the standard library's exception class. For example:

#include <iostream>
#include <stdexcept>

using std::cout;
using std::endl;

int main() {
    try {
        throw std::logic_error("Exception");
        throw std::bad_alloc;
    } catch(std::exception &ex) {
        cout << ex.what() << endl;
    }

    return 0;
}

I passed a reference in the exception handler because that means you can catch anything derived from std::exception, and still be able to get the proper information off it.

[kedaman]

what if you made something like this:

template <const char* T>class Exception{};
...
try{
throw Exception<"File not found">();
}
catch(Exception<"File not found">){
}

[parksie]

That won't work unless the compiler optimises the two strings down to exactly the same pointer (since they're the same string - it's the "Eliminate Duplicate Strings" option in MSVC).

And how do you catch any kind of Exception object?

[kedaman]

just regular inheritance, btw it didn't work :s

[parksie]

Didn't think it would - anyway, for exception handling virtual inheritance is perfectly okay. The performance aspect goes pretty much out of the window in an exceptional case.