How much null checking is enough?

Question

What are some guidelines for when it is not necessary to check for a null?

A lot of the inherited code I\'ve been working on as of late has null-checks

Answer 1

Older versions of Microsoft C++ (and probably others) did not throw an exception for failed allocations via new, but returned NULL. Code that had to run in both standard-conforming and older versions would have the redundant checking that you point out in your first example.

It would be cleaner to make all failed allocations follow the same code path:

if(obj==NULL)
    throw std::bad_alloc();