MSC12-C. Detect and remove code that has no effect

Code that is executed but does not perform any action, or has an unintended effect, most likely results from a coding error and can result in unexpected behavior. Statements or expressions that have no effect should be identified and removed from code. Most modern compilers can warn about code that has no effect in many cases (see MSC00-C. Compile cleanly at high warning levels).

This recommendation is related to MSC07-C. Detect and remove dead code.

Noncompliant Code Example (Assignment)

In this noncompliant code example, the comparison of a to b has no effect.

int a;
int b;
/* ... */
a == b;

This is likely a case of the programmer mistakenly using the equals operator == instead of the assignment operator =.

Compliant Solution (Assignment)

The assignment of b to a is now properly performed.

int a;
int b;
/* ... */
a = b;

Noncompliant Code Example (Dereference)

In this example, p is incremented and then dereferenced. However, *p has no effect.

int *p;
/* ... */
*p++;

Compliant Solution (Dereference)

Correcting this example depends on the intent of the programmer. For instance, if dereferencing p was a mistake, then p should not be dereferenced.

int *p;
/* ... */
p++;

If the intent was to increment the value referred to by p, then parentheses can be used to ensure p is dereferenced and then incremented (see EXP00-C. Use parentheses for precedence of operation).

int *p;
/* ... */
(*p)++;

Compliant Solution (Memory Mapped Devices)

Another possibility is that p is being used to reference a memory-mapped device. In this case, the variable p should be declared as volatile.

volatile int *p;
/* ... */
(void) *p++;

Risk Assessment

The presence of code that has no effect can indicate logic errors that may result in unexpected behavior and vulnerabilities.

Automated Detection

The LDRA tool suite V 7.6.0 can detect violations of this recommendation.

Splint Version 3.1.1 can detect violations of this recommendation.

The Coverity Prevent NO_EFFECT checker finds statements or expressions that do not accomplish anything, or statements that perform an unintended action.

GCC Compiler can detect violations of this recommendation when the -Wall flag is used.

The Klocwork INC.EXTRA checker can detect violations of this rule.

Related Vulnerabilities

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

Other Languages

This rule appears in the C++ Secure Coding Standard as MSC12-CPP. Detect and remove code that has no effect.

References

[[Coverity 07]]
[[ISO/IEC PDTR 24772]] "BRS Leveraging human experience," "BVQ Unspecified Functionality," "KOA Likely incorrect expressions," and "XYQ Dead and Deactivated Code"
[[MISRA 04]] Rule 14.1 and Rule 14.2

      49. Miscellaneous (MSC)