Why Doesn't My Non-Void C Function Returning No Value Produce a Compiler Error?

Non-Void Function Does Not Return a Value in C Code

Question:

This C code below has a non-void function that does not return a value:

static tvec4 Min(const tvec4& a, const tvec4& b, tvec4& out)
{
    tvec3::Min(a,b,out);
    out.w = min(a.w,b.w);
}

Why does it compile without an error?

Answer:

This behavior is undefined according to the C 11 draft standard section 6.6.3 paragraph 2, which states that flowing off the end of a value-returning function results in undefined behavior.

Compiler Warnings and Errors:

• gcc and clang: Can generate a warning using the -Wall flag (warning: control reaches end of non-void function [-Wreturn-type]). This can be converted to an error using the -Werror=return-type flag.
• Visual Studio: Generates error C4716 ('Min' : must return a value) by default, or warning C4715 if not all code paths return a value.

Implications:

Undefined behavior can lead to unpredictable results, including program crashes. It is recommended to use compiler options such as -Wall and -Wextra to detect and fix instances of undefined behavior.

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