The C99 language standard provides a mechanism for the programmer to inform the compiler that an array parameter contains a specified minimum number of elements. Some compilers are able to take advantage of this information to generate more efficient code for some types of processor.

If the guarantee made by the programmer is not honoured, and the number of elements is less than the minimum specified, the behaviour is undefined.

The processors used in typical embedded applications are unlikely to provide the facilities required to take advantage of the additional information provided by the programmer. The risk of the program failing to meet the guaranteed minimum number of elements outweighs any potential performance increase.

Example

There is no use of this C99 language feature that is compliant with this rule. The examples show some of the undefined behaviour that can arise from its use.

/* Non-compliant - uses static in array declarator */ 
uint16_t total ( uint16_t n, uint16_t a[ static 20 ] ) 
{
  uint16_t i;
  uint16_t sum = 0U;

  /* Undefined behaviour if a has fewer than 20 elements */ 
  for ( i = 0U; i < n; ++i ) 
  {
    sum = sum + a[ i ]; 
  }

  return sum; 
}
extern uint16_t v1[ 10 ]; 
extern uint16_t v2[ 20 ];

void g ( void ) 
{
  uint16_t x;

  x = total ( 10U, v1 );  /* Undefined - v1 has 10 elements but needs 
                           *             at least 20                   */ 
  x = total ( 20U, v2 );  /* Defined but non-compliant                 */ 
}

MISRA.FUNC.ARRAY.PARAM.STATIC.2012

MISRA C 2012 Rule 17.6: The declaration of an array parameter shall not contain the static keyword between the [ ]

Rationale

Example

See also