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c++exceptionthrow
Casey
Casey

Reputation: 10946

C++: Throwing exceptions, use 'new' or not?

Is it proper to use throw new FoobarException(Baz argument); or throw FoobarException(Baz argument);?

When catching I always use catch(FoobarException& e) "just in case" but I never could find a solid answer whether I had to use new or not in C++ (Java definitely) or if it was just a preference of the programmer.

Upvotes: 28

Views: 8897

Answers (2)

Sven
Sven

Reputation: 22693

Exceptions in C++ should be thrown by value, and caught by reference.

So this is the proper way:

try
{
    throw FoobarException(argument);
}
catch( const FoobarException &ex )
{
    cout << ex.what() << endl;
}

Don't throw an exception created with new, since who's responsible for deleting it is not well-defined. In addition, performing allocations during error handling can throw another exception, obscuring the original problem.

You don't have to catch by const reference (non-const will work fine), but I like doing it anyway. You should however always by reference (not by value) to catch the exception polymorphically. If you don't, the exception's type could be sliced.

Upvotes: 35

Evan Teran
Evan Teran

Reputation: 90503

unless there is some special requirement not to, I always throw by value and catch by const reference. This is because the new itself could throw an exception as well, during error handling, it is best to avoid things which can cause exceptions.

Upvotes: 8

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