C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 17:
17.1 What are some ways try / catch / throw can improve software quality?
17.2 Do the benefits of exceptions show up with tiny programs?
17.3 How do exceptions simplify my function return type and parameter types?
17.4 Do exceptions separate the "happy path" from the "bad path"?
17.5 Okay, so you're saying exception handling is easy and simple, right?
17.6 Mindset and discipline for exception handling?
17.7 I have too many try blocks; what can I do about it?
17.8 How can I handle a constructor that fails?
17.9 How can I handle a destructor that fails?
17.10 How should I handle resources if my constructors may throw exceptions?
17.11 How to prevent memory leaks when exceptions are thrown?
17.12 What should I throw?
17.13 What should I catch?
17.14 But MFC seems to encourage the use of catch-by-pointer; should I do the same?
17.15 Meaning and use of throw; (without an object)?
17.16 How do I throw polymorphically?
17.17 When I throw this object, how many times will it be copied?
[17.13] What should I catch?

In keeping with the C++ tradition of "there's more than one way to do that" (translation: "give programmers options and tradeoffs so they can decide what's best for them in their situation"), C++ allows you a variety of options for catching.

  • You can catch by value.
  • You can catch by reference.
  • You can catch by pointer.

In fact, you have all the flexibility that you have in declaring function parameters, and the rules for whether a particular exception matches (i.e., will be caught by) a particular catch clause are almost exactly the same as the rules for parameter compatibility when calling a function.

Given all this flexibility, how do you decide what to catch? Simple: unless there's a good reason not to, catch by reference. Avoid catching by value, since that causes a copy to be made and the copy can have different behavior from what was thrown. Only under very special circumstances should you catch by pointer.