CODEWITHSUNDEEP
cfunctionreturnbooleanc89
user12316583
user12316583

Reputation:

Not using the returned values sometimes returns both true and false in similar conditions

According to C89 standard the following code is legit:

A_Function_that_returns_true();

But the following is false (Since the returned value is not used-This can be solved simply by declaring a bool variable)

(5>3) && (7>6);

But what’s the difference between both examples? In both I didn’t use the returned value so why one is true and one is false that doesn’t sound right

Upvotes: 0

Views: 63

Answers (1)

Steve Summit
Steve Summit

Reputation: 47923

It is not a violation of the C Standard to discard the result of an expression. Neither of the two expression statements in the question violates any rule or constraint.

Whether a compiler chooses to emit helpful warnings about various things is a quality-of-implementation issue, not governed by the Standard.

Calling a function but then not using its return value usually isn't a problem, because many (though certainly not all) functions do something other than just compute and return a value. (The formal term for this is that many functions have side effects.)

The expression

(5>3) && (7>6);

is, on the other hand, perfectly useless. It's clear that it doesn't do anything (it has no side effects), so the compiler is well advised to warn against it.

If a compiler writer decided to also helpfully warn about function return values that were ignored, there would be an immediate problem: virtually every C program contains multiple calls to printf, for which the return value is not checked. So there would be so many false positives that the warning would be useless.

Upvotes: 2

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