MISRA C:2012 Rule 12.3

The comma operator should not be used

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Description

Note

Using Code Prover for checking coding rules is no longer supported. See Version History.

Rule Definition

The comma operator should not be used.

Rationale

The comma operator can be detrimental to readability. You can often write the same code in another form.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

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Comma Usage in C Code

typedef signed int abc, xyz, jkl;
static void func1 ( abc, xyz, jkl );       /* Compliant - case 1 */
int foo(void)
{
    volatile int rd = 1;                   /* Compliant - case 2*/
    int var=0, foo=0, k=0, n=2, p, t[10];  /* Compliant - case 3*/
    int abc = 0, xyz = abc + 1;            /* Compliant - case 4*/
    int jkl = ( abc + xyz, abc + xyz );    /* Noncompliant - case 1*/
    var = 1, foo += var, n = 3;          /* Noncompliant - case 2*/ 
    var = (n = 1, foo = 2);              /* Noncompliant - case 3*/
    for ( int *ptr = &t[ 0 ],var = 0 ;
          var < n; ++var, ++ptr){}    /* Noncompliant - case 4*/
    if ((abc,xyz)<0) { return 1; }         /* Noncompliant - case 5*/
}

In this example, the code shows various uses of commas in C code.

Noncompliant Cases

Case	Reason for noncompliance
1	When reading the code, it is not immediately obvious what `jkl` is initialized to. For example, you could infer that `jkl` has a value `abc+xyz`, `(abc+xyz)*(abc+xyz)`, `f((abc+xyz),(abc+xyz))`, and so on.
2	When reading the code, it is not immediately obvious whether `foo` has a value 0 or 1 after the statement.
3	When reading the code, it is not immediately obvious what value is assigned to `var`.
4	When reading the code, it is not immediately obvious which values control the `for` loop.
5	When reading the code, it is not immediately obvious whether the `if` statement depends on `abc`, `xyz`, or both.

Compliant Cases

Case	Reason for compliance
1	Using commas to call functions with variables is allowed.
2	Comma operator is not used.
3 & 4	When using the comma for initialization, the variables and their values are immediately obvious.

Check Information

Group: Expressions

Category: Advisory

AGC Category: Advisory

Version History

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R2024a: Using Code Prover to check for coding rule violations is no longer supported

Checking for coding rule violations and computing code metrics by using Code Prover is no longer supported. To check for coding rule violations and to compute code metrics, use Bug Finder. See Migrate Code Prover Workflows for Checking Coding Standards and Code Metrics to Bug Finder.

R2022a: Using Code Prover to check for coding rule violations is not recommended

Checking for coding rule violations and computing code metrics by using Code Prover is not recommended. This workflow will be removed in a future release. To check for coding rule violations and to compute code metrics, use Bug Finder. See Migrate Code Prover Workflows for Checking Coding Standards and Code Metrics to Bug Finder. To see how Bug Finder checks this rule, see MISRA C:2012 Rule 12.3.