Why should I always enable compiler warnings?

Question

I often hear that when compiling C and C++ programs I should \"always enable compiler warnings\". Why is this necessary? How do I do that?

Sometimes I also hear tha

Answer 1

Warnings consist of the best advice some of the most skilled C++ developers could bake into an application. They're worth keeping around.

C++, being a Turing complete language, has plenty of cases where the compiler must simply trust that you knew what you are doing. However, there are many cases where the compiler can realize that you probably did not intend to write what you wrote. A classic example is printf() codes which don't match the arguments, or std::strings passed to printf (not that that ever happens to me!). In these cases, the code you wrote is not an error. It is a valid C++ expression with a valid interpretation for the compiler to act on. But the compiler has a strong hunch that you simply overlooked something which is easy for a modern compiler to detect. These are warnings. They are things that are obvious to a compiler, using all the strict rules of C++ at its disposal, that you might have overlooked.

Turning warnings off, or ignoring them, is like choosing to ignore free advice from those more skilled than you. Its a lesson in huberis that ends either when you fly too close to the sun and your wings melt, or a memory corruption error occurs. Between the two, I'll take falling from the sky any day!

"Treat warnings as errors" is the extreme version of this philosophy. The idea here is that you resolve every warning the compiler gives you -- you listen to every bit of free advice and act on it. Whether this is a good model for development for you depends on the team and what kind of product you are working on. It's the ascetic approach that a monk might have. For some, it works great. For others, it does not.

On many of my applications we do not treat warnings as errors. We do this because these particular applications need to compile on several platforms with several compilers of varying ages. Sometimes we find it is actually impossible to fix a warning on one side without it turning into a warning on another platform. So we are merely careful. We respect warnings, but we don't bend over backwards for them.