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?
[17.17] When I throw this object, how many times will it be copied?

Depends. Might be "zero."

Objects that are thrown must have a publicly accessible copy-constructor. The compiler is allowed to generate code that copies the thrown object any number of times, including zero. However even if the compiler never actually copies the thrown object, it must make sure the exception class's copy constructor exists and is accessible.