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Showing posts from February, 2006

Functions inside constructor should throw (if they fail)

This is a for constructors, which do non-trivial resource allocation and initialization using helper member functions in the class. Exceptions raised in such member functions should be propagated upto the constructor and not eat them. In other words, such member functions should throw exception if they can't satisfy their contract even though they provide strong exception safety guarantee. Exception propagated upto the constructor will be automatically propagated where the object is being constructed indicating failure in object construction. Otherwise, silently eating exceptions during object initialization will create an object in an inconsistent state. The scope in which it is created will never know that actually the object construction failed. If object construction can be reasonably performed even in the face of exception, then it need not be propagated out. Example, LStack: A Stack implemented as a linked-list. LStack::LStack (const LStack & s) { this->copy_all_

Why overloaded ++ operator signatures are different?

The canonical form of overloaded pre-increment and post-increment operators for class Foo are declared in the following way in C++. /// Preincrement operator Foo & operator++ (void); /// Postincrement operator const Foo operator++ (int); The int in the post-increment operator is obviously to disambiguate between post and pre forms of the operator. Then, why is the return type different? As many other C++ features, this one also has a subtle meaning! In C++, for ints, you can write ++i = k; but not, i++ = k; This is because, i++ results in a Rvalue to which you can't assign. Unlike i++, ++i results in a Lvalue to which you can assign which is infact ( incremented ) i itself. Not that ++i = k; has a great importance, but it is a fact that C++ has been designed that way. I would be interested in knowing the reason. One reason is that i++ = k; is not allowed is that it is just ambiguous. but ++i = k; is not ambiguous. A const in the return type is also requir