Many functions return useful values whether or not the function has side effects. In most cases, this value is used to signify whether the function successfully completed its task or if some error occurred (see ERR02-A. Avoid in-band error indicators). Other times, this the value is the result of some computation and is a necessary output.
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Section 6.8.3 of C99 states that: \[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] states that |
The expression in an expression statement is evaluated as a
voidexpression for its side effects.
All expression statements, such as function calls with an ignored value, are implicitly cast to void. Since a return value often contains important information about possible errors, it should always be checked; otherwise, otherwise the cast should be made explicit to signify programmer intent. If a function returns no meaningful value, it should be declared with return type void.
This recommendation encompasses MEM32-C. Detect and handle memory allocation errors, FIO04-A. Detect and handle input and output errors, and FIO34-C. Use int to capture the return value of character IO functions.
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