c++ - g++ How to get warning on ignoring function return value

Question

lint produces some warning like:

foo.c XXX Warning 534: Ignoring return value of function bar()

From the lint manual

534 Ignoring return value of function

'Symbol' (compare with Location) A function that returns a value is called just for side effects as, for example, in a statement by itself or the left-hand side of a comma operator. Try: (void) function(); to call a function and ignore its return value. See also the fvr, fvo and fdr flags in §5.5 "Flag Options".

I want to get this warning, if there exists any, during compilation. Is there any option in gcc/g++ to achieve this? I had turned on -Wall but that apparently did not detect this.

Answer 1

Since C++17 you can use the [[nodiscard]] attribute.

Example:

[[nodiscard]] int bar() {
  return 42;
}