MISRA.FUNC.MODIFIEDPAR.2012

MISRA C 2012 Rule 17.8: A function parameter should not be modified

A function parameter should not be modified

Category: Advisory

Analysis: Undecidable, System

Applies to: C90, C99

Rationale

A function parameter behaves in the same manner as an object that has automatic storage duration. While the C language permits parameters to be modified, such use can be confusing and conflict with programmer expectations. It may be less confusing to copy the parameter to an automatic object and modify that copy. With a modern compiler, this will not usually result in any storage or execution time penalty.

Programmers who are unfamiliar with C, but who are used to other languages, may modify a parameter believing that the effects of the modification will be felt in the calling function.

Example

int16_t glob = 0;

void proc ( int16_t para ) 
{
  para = glob;                /* Non-compliant */ 
}

void f ( char *p, char *q ) 
{
  p = q;                      /* Non-compliant */ 
  *p = *q;                    /* Compliant     */ 
}