Should Compilers Throw Errors for Functions Lacking Return Values in C ?

Is it Acceptable for Compilers to Return Garbage When a Function Declares a Non-Void Return Type but Fails to Return a Value?

The absence of a return statement in a function with a non-void return type raises questions about compiler behavior. While the compiler may seem to return garbage in such cases, this is not an ideal solution.

Why Isn't it an Error?

In C , functions without a return value exhibit undefined behavior. However, most compilers issue warnings instead of errors. This is because it's not always straightforward for compilers to determine whether a function actually runs off the end or exits through an exception.

Consider the following example:

int func1() {
    return; // error
}

int func2() {
    // does not return anything
}

In this case, func2 should theoretically trigger an error, but it doesn't. This is because the compiler cannot guarantee that func2 won't exit via an exception, making it difficult to prove that it actually runs off the end of the function.

Why Shouldn't it Throw an Error?

Unlike uninitialized variables, which are clearly problematic, a function's lack of a return value may not always be an issue. For example:

int func3() {
    func4();
}

If func4 throws an exception, then func3's missing return value is immaterial. However, the compiler cannot always determine whether func4 will throw or not, especially when considering separately compiled code.

In conclusion, while C 's undefined behavior for functions without a return value is not ideal, compilers generally issue warnings rather than errors to avoid potential false positives due to the complexity of determining a function's actual execution path.

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