Why Does Omitting a Return Statement in a C Function Lead to Undefined Behavior?

Omitting Return Statement in C : Unexpected Behavior

In C , omitting a return statement in a non-void function can lead to Undefined Behaviour. However, in certain cases, it may appear that the code behaves correctly despite the missing return.

This seemingly innocuous omission arises from the fact that when the control flow of a function reaches its end without a return statement, the compiler interprets it as an implicit return statement with no value. This behavior is applicable to all non-void functions, excluding the main() function.

While this practice may occasionally result in seemingly correct output, it is crucial to understand that such code invokes Undefined Behaviour. As per ISO C -98 (Section 6.6.3/2), flowing off the end of a function in a value-returning function leads to Undefined Behaviour.

In the example provided, omitting the return statement in the getBound function should have resulted in a compiler error or warning. However, certain versions of g may allow this and compile the code without an error. It is important to note that this is not a standard behavior and should not be relied upon.

To ensure correct program execution and avoid Undefined Behaviour, it is essential to explicitly include a return statement in all non-void functions. Always use the -Wall option when compiling C code to catch potential warnings and avoid such issues.

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