Why Do C Compilers Treat Non-Void Functions Without Explicit Returns Differently?

Compiler Toleration of Non-Value-Returning Function

In C , a non-void function is expected to return a value. However, in certain scenarios, a function may appear to not return a value, leading to questions about its behavior.

Observed Behavior

The provided code snippet declares a non-void function, Min, that doesn't explicitly return a value. Instead, it updates a reference parameter, out, with the desired result.

Standard Compliance

According to the C 11 draft standard, not providing a return value in a non-void function constitutes undefined behavior. This means that the compiler is not obligated to issue an error or warning, as it may be difficult to accurately determine the intent in all cases.

Compiler Behavior

Despite the standard's ambiguity, certain compilers like GCC and Clang may issue warnings with the -Wall flag, notifying of a potential issue. By leveraging the -Werror=return-type flag, these warnings can be converted into errors.

Visual Studio Behavior

In Microsoft Visual Studio, code similar to the provided snippet would generate an error (C4716) by default, enforcing the expectation that non-void functions should return a value.

Undefined Behavior Alert

It's important to note that relying on undefined behavior is not recommended. While some compilers may provide warnings or errors, others may simply ignore the issue, potentially leading to unexpected or erroneous program execution.

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