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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 value is the result of some computation and is a necessary output.

Section 6.8.3 of C99 states that: \[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\]

The expression in an expression statement is evaluated as a void expression 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 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 is a general recommendation encompassing 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.WRITE ME ALEX

Non-Compliant Code Example

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(void) strcpy(dst, src);

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Risk Assessment

Failure to handle error codes or other values returned by functions can lead to incorrect program flow and violations of data integrity.

Automated Detection

Splint Version 3.1.1 can detect violations of this rule.

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\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.8.3, "Expression and null statements"

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EXP11-A. Do not apply operators expecting one type to data of an incompatible type      03. Expressions (EXP)       EXP30-C. Do not depend on order of evaluation between sequence points