MISRA.LOGIC.PRIMARY

Operand in a logical 'and' or 'or' expression is not a primary expression.

MISRA-C Rule 12.5 (required): The operands of a logical && or || shall be primary-expressions.

"Primary expressions" are defined in ISO/IEC 9899:1990 [2], section 6.3.1. Essentially they are either a single identifier, or a constant, or a parenthesised expression. The effect of this rule is to require that if an operand is other than a single identifier or constant then it must be parenthesised. Parentheses are important in this situation both for readability of code and for ensuring that the behaviour is as the programmer intended. Where an expression consists of either a sequence of only logical && or a sequence of only logical ||, extra parentheses are not required.

Example

if ( ( x == 0 ) && ishigh )   /* make x == 0 primary       */
if ( x || y || z )            /* exception allowed,
                                 if x, y and z are Boolean */
if ( x || ( y && z ) )        /* make y && z primary       */
if ( x && ( !y ) )            /* make !y primary           */
if ( ( is_odd (y) ) && x )    /* make call primary         */

Where an expression consists of either a sequence of only logical && or a sequence of only logical ||, extra parentheses are not required.

if ( ( x > c1) && (y > c2) && (z > c3) )   /* Compliant               */
if ( ( x > c1) && (y > c2) || (z > c3) )   /* not compliant           */
if ( ( x > c1) && ((y > c2) || (z > c3)) ) /* Compliant extra () used */

Note that this rule is a special case of Rule 12.1.