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

c++ exception throw
Casey picture Casey · Jul 23, 2011 · Viewed 7.9k times · Source

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.

Answer

Sven picture Sven · Jul 23, 2011

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.

Related questions

Throwing exceptions from constructors

I'm having a debate with a co-worker about throwing exceptions from constructors, and thought I would like some feedback. Is it OK to throw exceptions from constructors, from a design point of view? Lets say I'm wrapping a POSIX mutex …

Read More
How do exceptions work (behind the scenes) in c++

I keep seeing people say that exceptions are slow, but I never see any proof. So, instead of asking if they are, I will ask how do exceptions work behind the scenes, so I can make decisions of when to …

Read More
Should I use an exception specifier in C++?

In C++, you can specify that a function may or may not throw an exception by using an exception specifier. For example: void foo() throw(); // guaranteed not to throw an exception void bar() throw(int); // may throw an exception of …

Read More