MISRA.ASSIGN.SUBEXPR.2012

MISRA C 2012 Rule 13.4: The result of an assignment operator should not be used

The result of an assignment operator is used.

C90 [Unspecified 7, 8; Undefined 18], C99 [Unspecified 15, 18; Undefined 32]

[Koenig 6]

Category: Advisory

Analysis: Decidable, Single Translation Unit

Applies to: C90, C99

Amplification

This rule applies even if the expression containing the assignment operator is not evaluated.

Rationale

The use of assignment operators, simple or compound, in combination with other arithmetic operators is not recommended because:

• It can significantly impair the readability of the code;
• It introduces additional side effects into a statement making it more difficult to avoid the undefined behaviour covered by Rule 13.2.

Example

x = y;                                /* Compliant                           */ 
a[ x ] = a[ x = y ];                  /* Non-compliant - the value of x = y
                                       * is used                             */

/*
 * Non-compliant - value of bool_var = false is used but 
 * bool_var == false was probably intended 
 */ 
if ( bool_var = false ) 
{ 
}

/* Non-compliant even though bool_var = true isn't evaluated                 */ 
if ( ( 0u == 0u ) || ( bool_var = true ) ) 
{ 
}

/* Non-compliant - value of x = f() is used                                  */ 
if ( ( x = f ( ) ) != 0 ) 
{ 
}

/* Non-compliant - value of b += c is used                                   */ 
a[ b += c ] = a[ b ];


/* Non-compliant - values of c = 0 and b = c = 0 are used                    */ 
a = b = c = 0;

See also

Rule 13.2