MISRA C:2012 Dir 4.4

Sections of code should not be "commented out"

Description

Directive Definition

Sections of code should not be "commented out".

Rationale

C comments enclosed in /* */ do not support nesting. A comment beginning with /* ends at the first */ even when the */ is intended as the end of a later nested comment. If a section of code that is commented out already contains comments, you can encounter compilation errors (or at least comment out less code than you intend).

Commenting out code is not a good practice. The commented out code can remain out of sync with the surrounding code without causing compilation errors. Later, if you uncomment the code, you can encounter unexpected issues.

Use comments only to explain aspects of the code that are not apparent from the code itself.

Polyspace Implementation

The checker uses internal heuristics to detect commented out code. For instance, characters such as #, ;, { or } indicate comments that might potentially contain code. These comments are then evaluated against other metrics to determine the likelihood of code masquerading as comment. For instance, several successive words without a symbol in between reduces this likelihood.

The checker does not flag the following comments even if they contain code:

Doxygen comments beginning with /**, /*!, /// or //!.

Comments that repeat the same symbol several times, for instance, the symbol = here:

/* =====================================
 * A comment
 * =====================================*/

Comments on the first line of a file.
Comments that mix the C style (/* */) and C++ style (//).

The checker considers that these comments are meant for documentation purposes or entered deliberately with some forethought.

Troubleshooting

If you expect a rule violation but do not see it, refer to the documentation of Polyspace^® Code Prover™ or Polyspace Code Prover Server™.

Examples

expand all

Code Commented Out

#include <stdlib.h>

int32_t getRandInt();
void print32_t(int32_t);

/* Function to print32_t random int32_tegers*/ 
void print32_tInteger() {
    /* int32_t val = getRandInt(); 
     * val++; 
     * print32_t(val); */     
    print32_t(getRandInt());
}

This example contains a block of commented out code that violates the rule.

Check Information

Group: Code design

Category: Advisory

AGC Category: Advisory

Introduced in R2020b

Documentation