Rule Definition
The conversion of a function pointer into or from any of: • Pointer to object; • Pointer to incomplete; • void * results in undefined behaviour. If a function is called by means of a pointer whose type is not compatible with the called function, the behaviour is undefined. Conversion of a pointer to a function into a pointer to a function with a different type is permitted by The Standard. Conversion of an integer into a pointer to a function is also permitted by The Standard. However, both are prohibited by this rule in order to avoid the undefined behaviour that would result from calling a function using an incompatible pointer type.

Violation Code Sample

typedef void ( *fp16 ) ( int16_t n );
typedef void ( *fp32 ) ( int32_t n );
#include <stdlib.h> /* To obtain macro NULL */

fp32 fp2 = ( fp32 ) fp1; /* Non-compliant - function
* pointer into different
* function pointer */

fp16 fp3 = ( fp16 ) 0x8000; /* Non-compliant - integer into
* function pointer */
fp16 fp4 = ( fp16 ) 1.0e6F; /* Non-compliant - float into
* function pointer */

Fixed Code Sample

fp16 fp1 = NULL; /* Compliant - exception 1 */

if ( fp2 != NULL ) /* Compliant - exception 1 */
{
}


typedef fp16 ( *pfp16 ) ( void );
pfp16 pfp1;
( void ) ( *pfp1 ( ) ); /* Compliant - exception 2 - cast function
* pointer into void




extern void f ( int16_t n );
f ( 1 ); /* Compliant - exception 3 - implicit conversion
* of f into pointer to function */
fp16 fp5 = f; /* Compliant - exception 3

Standards Reference: MISRA 2012 C - 11.1: Conversions shall not be performed between a pointer to a function and any other type MISRA 2008, C++,5-2-6: A cast shall not convert a pointer to a function to any other pointer type, including a pointer to function type. AUTOSAR 2014, C++, Rule M5-2-6: A cast shall not convert a pointer to a function to any other pointer type, including a pointer to function type.