MISRA C:2023 Rule 11.1

Conversions shall not be performed between a pointer to a function and any other type

Since R2024a

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Description

Rule Definition

Conversions shall not be performed between a pointer to a function and any other type¹ .

Rationale

The rule forbids the following two conversions:

Conversion from a function pointer to any other type. This conversion causes undefined behavior.
Conversion from a function pointer to another function pointer, if the function pointers have different argument and return types.
The conversion is forbidden because calling a function through a pointer with incompatible type results in undefined behavior.

Polyspace Implementation

Polyspace^® considers both explicit and implicit casts when checking this rule. However, casts from NULL or (void*)0 do not violate this rule.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

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Cast between two function pointers

typedef void (*fp16) (short n);
typedef void (*fp32) (int n);

#include <stdlib.h>                     /* To obtain macro  NULL */

void func(void) {   /* Exception 1 - Can convert a null pointer 
                     * constant into a pointer to a function */
  fp16 fp1 = NULL;                 /* Compliant - exception  */
  fp16 fp2 = (fp16) fp1;           /* Compliant */
  fp32 fp3 = (fp32) fp1;           /* Non-compliant */
  if (fp2 != NULL) {}              /* Compliant - exception  */
  fp16 fp4 = (fp16) 0x8000;        /* Non-compliant - integer to 
                                    * function pointer */}

In this example, the rule is violated when:

The pointer fp1 of type fp16 is cast to type fp32. The function pointer types fp16 and fp32 have different argument types.
An integer is cast to type fp16.

The rule is not violated when function pointers fp1 and fp2 are cast to NULL.

Check Information

Group: Pointer Type Conversions

Category: Required

AGC Category: Required

Version History

Introduced in R2024a