CODEWITHSUNDEEP
c++exception
Smithy
Smithy

Reputation: 1187

catch(...) does not catch all exceptions

I've run into a problem regarding exceptions.

The code is shown below,

try
{
    auto it = set_difference(allInterfaces.begin(), allInterfaces.end(), eths.begin(),   
    eths.end(), newCards.begin());
}  
catch(...)
{
  cout << "exception thrown << endl;
}

I know set_difference() is throwing an exception but the programs exits and the catch block doesn't catch the exception. Is there a way to catch the exception? I thought the catch all should always work.

Thanks for any help.

Upvotes: 0

Views: 336

Answers (2)

Praetorian
Praetorian

Reputation: 109089

set_difference will write the elements that are unique to either of the input sets to the output range you pass in. It's your responsibility to ensure that that range is large enough to contain the result. Otherwise, you'll walk off beyond the bounds of the range, resulting in undefined behavior. No exception is thrown when this happens, the best indicator you can hope for is an assertion failure in unoptimized builds (and there's no guarantee for that either).

Assuming newCards is a container that supports push_back, the easiest way to prevent this is to use std::back_insert_iterator, which will call push_back every time an object is assigned to it.

auto it = set_difference(allInterfaces.begin(), allInterfaces.end(), 
                         eths.begin(), eths.end(), std::back_inserter(newCards));

The other options available are std::front_insert_iterator (calls push_front()) and std::insert_iterator (calls insert()). Choose the one that suits your needs best.

Upvotes: 2

Some programmer dude
Some programmer dude

Reputation: 409136

With the help of your comment, it's very likely that you increase and iterate the iterator returned from newCards.begin(), even beyond the bounds of the vector. This leads to undefined behavior (which in your case causes a crash) and not to a thrown C++ exception. Iterator access is not bounds-checked in C++ (very few things are).

To solve this you need to pass in the end of the newCards vector as well, and make sure you don't step out of bounds.

Upvotes: 1

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