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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-AC. Avoid in-band error indicators). Other times, the value is the result of some computation and is a necessary output.

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This recommendation encompasses MEM32-C. Detect and handle memory allocation errors, FIO04-AC. 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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Noncompliant Code Example

This non-compliant noncompliant code example calls puts() and fails to check whether a write error occurs.

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However, puts() can fail and return EOF. If the output were determined to be critical, then the return value should have been checked.

Compliant Solution

This compliant solution checks to make sure no output error occurred (see FIO04-AC. Detect and handle input and output errors).

if (puts("foo") == EOF) {
  /* Handle Error */
}

Exceptions

EXP12-EX1: If the return value is inconsequential or if any errors can be safely ignored, such as for functions called because of their side effects, the function should be explicitly cast to void to signify programmer intent. See the compliant solution for removing an existing destination file in FIO10-AC. Take care when using the rename() function for an example of this exception.

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strcpy(dst, src);

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 recommendation.

Compass/ROSE can detect violations of this recommendation.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.8.3, "Expression and null statements"
\[[ISO/IEC PDTR 24772|AA. C References#ISO/IEC PDTR 24772]\] "CSJ Passing Parameters and Return Values"

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