Safe C++

Chapter 2. When to Catch a Bug

Why the Compiler Is Your Best Place to Catch Bugs

Given the choice of catching bugs at compile time vs. catching bugs at runtime, the short answer is that you want to catch bugs at compile time if at all possible. There are multiple reasons for this. First, if a bug is detected by the compiler, you will receive a message in plain English saying exactly where, in which file and at which line, the error has occurred. (I may be slightly optimistic here, because in some cases—especially when STL is involved—compilers produce error messages so cryptic that it takes an effort to figure out what exactly the compiler is unhappy about. But compilers are getting better all the time, and most of the time they are pretty clear about what the problem is.)

Another reason is that a complete compilation (with a final link) covers all the code in the program, and if the compiler returns with no errors or warnings, you can be 100% sure that there are no errors that could be detected at compile time in your program. You could never say the same thing about run-time testing; with a large enough piece of code, it is difficult to guarantee that all the possible branches were tested, that every line of code was executed at least once.

And even if you could guarantee that, it wouldn’t be enough—the same piece of code could work correctly with one set of inputs and incorrectly with another, so with runtime testing you are never completely sure that you have tested everything. ...