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

It depends on the situation. The rest of my answer assumes C++.

• I never test the return value of new since all the implementations I use throw bad_alloc on failure. If I see a legacy test for new returning null in any code I'm working on, I cut it out and don't bother to replace it with anything.
• Unless small minded coding standards prohibit it, I assert documented preconditions. Broken code which violates a published contract needs to fail immediately and dramatically.
• If the null arises from a runtime failure which isn't due to broken code, I throw. fopen failure and malloc failure (though I rarely if ever use them in C++) would fall into this category.
• I don't attempt to recover from allocation failure. Bad_alloc gets caught in main().
• If the null test is for an object which is collaborator of my class, I rewrite the code to take it by reference.
• If the collaborator really might not exist, I use the Null Object design pattern to create a placeholder to fail in well defined ways.