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Comment Ratio

Ratio of number of lines that contain comments to the total number of lines in a file, expressed as percentage

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Description

This metric calculates the ratio of lines containing comments to total number lines in a file, expressed as a percentage.

This metric is equivalent to the Comment Frequency metric defined by European Cooperation for Space Standardization (ECSS). As defined by EECS, Polyspace® calculates the Comment ratio metric using this formula

Comment ratio = 100 * Number of lines containing comments / (Number of code lines without comments + Number of lines containing comments)
A line containing any syntactical token is considered a code line. Consider this code:
int foo() {
    // Comment line 1
    // Comment Line2
    // Comment line 3
    
    int x = 0; // Inline comment ignored for comment density but considered for comment ratio

    return x;
}
This code contains three code lines without comment:

  • int foo(){

  • return x

  • }

There are four lines containing comment:

  • // Comment line 1

  • // Comment line 2

  • // Comment line 3

  • int x = 0; // Inline comment ignored for comment density but considered for comment ratio

Polyspace calculates the Comment Frequency as 4/(4+3) × 100% or 57%

This metric is calculated differently than the Comment Density metric, which calculates comment density as defined by the Hersteller Initiative Software (HIS) code complexity standard:

  • Polyspace calculates the comment density after the preprocessing stage whereas the comment ratio is calculated before preprocessing.

  • When calculating the comment density, Polyspace counts the three consecutive comments in foo() as a single comment. When calculating comment ratio, each line of comment is counted separately.

  • When calculating comment density, Polyspace ignores comments that are appended to lines of code. Such comments are counted when calculating comment ratio.

Examples

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This example has two functions foo() and bar(). The code has 21 lines that contain comments, and 11 code lines that do not contain any comments.

/*=============================*/
/* external linkage functions  */
/*=============================*/

// routine foo
/* arg1:
 *
 * arg2:
 */
// return a negative in case of error
// Polyspace counts these consecutive lines of comments as a single comment for comment density, but counts them separately for comment ratio.


int /* return int type, counted as comment line
     counted as comment line*/ foo (
         /* void */ // counted as comment line
         ) { // counted as comment line 
    /* local variables */ // counted as comment line 
    int
        x; /* uninitailized at the declaration */ // counted as comment line 

    int r =
#if 1
        0;
#else
    -1;
#endif

    return r;
    /* same line as '}' counted as comment line   */ } /* this line still considered as containing comment
                                                       * As is this line
                                                       */
			 /* This is counted as a comment line 
                                        * even if not correctly indented. */
int bar() {
    return 1;
}

The comment ratio is therefore 100 × (21/(21+11)) = 66%.

Metric Information

Group: File
Acronym: COMR
HIS Metric : No

See Also