What Happens When You Omit a Return Statement in a Non-Void C Function?

Omitting Return Statement in C : A Risky Endeavor

In C , omitting a return statement in a non-void function (except for the main function) can lead to unpredictable consequences. Contrary to the confusion experienced by the user, g by default does not guess to return the last defined variable.

The C standard explicitly states that flowing off the end of a function without a return statement invokes undefined behavior in value-returning functions. This means that the compiler is not obligated to return any specific value, and the program may behave erratically or even crash.

Consider the example provided:

struct boundTag Box::getBound(int side) {
    struct boundTag retBoundTag;
    retBoundTag.box = this;
    // ... (code omitted)
}

Although this function lacks a return statement, it was observed that g compiled it without warnings. This is because the C compiler often generates a default return statement to handle the end of non-void functions without explicit returns. However, this practice is not guaranteed and can lead to unexpected results.

To ensure proper behavior, it is imperative to always include an explicit return statement in non-void functions. If the function is meant to return a value, such as a boundTag, the return statement should assign that value to the function's return type.

It is also recommended to compile C code with stricter options, such as -Wall, which will typically warn about the absence of return statements in non-void functions and other potential issues.

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