MISRA C:2023 Rule 14.4

The controlling expression of an if statement and the controlling expression of an iteration-statement shall have essentially Boolean type

Since R2024a

Description

Rule Definition

The controlling expression of an if statement and the controlling expression of an iteration-statement shall have essentially Boolean type¹

Rationale

Strong typing requires the controlling expression on an if statement or iteration statement to have essentially Boolean type.

Polyspace Implementation

Polyspace^® does not flag integer constants, for example if(2).

The analysis recognizes the Boolean types, bool or _Bool (defined in stdbool.h)

You can also define types that are essentially Boolean using the option Effective boolean types (-boolean-types).

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

Controlling Expression in if, while, and for

#include <stdbool.h>
#include <stdlib.h>

#define TRUE 1

typedef _Bool bool_t;
extern bool_t flag;

void foo(void){
    int *p = 1;
    int *q = 0;
    int i = 0;
    while(p){}           /* Non-compliant - p is a pointer */

    while(q != NULL){}   /* Compliant */

    while(TRUE){}        /* Compliant */

    while(flag){}        /* Compliant */

    if(i){}              /* Non-compliant - int32_t is not boolean */

    if(i != 0){}         /* Compliant */

    for(int i=-10; i;i++){}   /* Non-compliant - int32_t is not boolean */

    for(int i=0; i<10;i++){}  /* Compliant */
}

This example shows various controlling expressions in while, if, and for statements.

The noncompliant statements (the first while, if, and for examples), use a single non-Boolean variable. If you use a single variable as the controlling statement, it must be essentially Boolean (lines 17 and 19). Boolean expressions are also compliant with MISRA™.

Check Information

Group: Control Statement Expressions

Category: Required

AGC Category: Advisory

Version History

Introduced in R2024a