MISRA C:2012 Rule 13.4

The result of an assignment operator should not be used

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Description

Rule Definition

The result of an assignment operator should not be used.

Rationale

The rule is violated if the following happens in the same line of code:

The assignment operator acts on a variable.
Another read or operation is performed on the result of the assignment.

For example, the line a[x]=a[x=y]; violates this rule. The [] operator acts on the result of the assignment x=y.

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

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Result of Assignment Used

int x, y, b, c, d;
int a[10];
unsigned int bool_var, false=0, true=1;

int foo(void) {

    x = y;            /* Compliant - x is not used */

    a[x] = a[x = y];  /* Non-compliant - Value of x=y is used */

    if ( bool_var = false )/* Non-compliant - bool_var=false is used */
{}


    if ( bool_var == false ) {}   /* Compliant */

    if ( ( 0u == 0u ) || ( bool_var = true ) )/* Non-compliant */
                    /*- even though (bool_var=true) is not evaluated */
 {} 
    

    if ( ( x = f () ) != 0 )/* Non-compliant - value of x=f() is used */
 {} 
    a[b += c] = a[b];/* Non-compliant - value of b += c is used */
    b = c = d = 0; /* Non-compliant - value of d=0 and c=d=0 are used */

}

In this example, the rule is violated when the result of an assignment is used.

Check Information

Group: Side Effects

Category: Advisory

AGC Category: Advisory

Documentation