# V2590. MISRA. Conversions should not be performed between pointer to function and any other type.

This diagnostic rule is based on the MISRA (Motor Industry Software Reliability Association) software development standard.

This rule applies only to C. Type casting between a pointer to function and any other type causes undefined behavior. Type casting between pointers to functions of incompatible types causes undefined behavior when this function is called.

The example below demonstrates type casting between pointers to functions of incompatible types. Both casts are potentially fatal:

    void foo(int32_t x);
    typedef void (*fp)(int16_t x);

    void bar(void)
    {
      fp fp1 = (fp)&foo;
      int32_t(*fp2)(void) = (int32_t (*)(void))(fp1);
    }

The following code is incorrect because a pointer to a function is cast to other types:

    void* vp = (void*)fp1;
    int32_t i32 = (int32_t)foo;
    fp fp3 = (fp)i32;

Calling the function through pointers obtained in that way may lead to segmentation errors.

Exceptions:

Type casting between a null pointer constant and a pointer to a function is possible:

    fp fp3 = NULL;

Casting between a pointer to a function and the 'void' type:

    (void) fp4;

Implicit casting between a function and a pointer to the same function:

    (void(*)(int32_t)) foo;

This diagnostic is classified as:

MISRA-C-2012-11.1 MISRA-C-2023-11.1