Typecasting a function pointer

Question

I know this is a duplicate. I've searched already but none address the problem I'm having. NOTE in an attempt to single out my confusion I have tried to simplify the typecast from the original. Hopefully it isn't undefined behaviour Declaring a pointer to a function ``` Int (*funcPtr)(void*,void*); ``` Strcmp declaration ``` int strcmp (char *, char *); ``` Typecasting a function pointer ``` FuncPtr = (int (*)(void*, void*))strcmp ``` This is where I get confused. I understand Typecasting a function pointer we have created. So type casting FuncPtr for example just changes what type of function funcPtr can point to. I have also read that the name of a function Is a function pointer to itself so Typecasting strcmp and using my understanding from above, ``` int (*)(void*, void*))strcmp ``` Strcmp can now point to a function that takes two pointers to void and returns an int which Is clearly wrong as like arrays I think the function name can't be a pointer to another function. Because of…

Accepted Answer

There are functions and there are function pointers. `strcmp` is a function, linked to your project. When the identifier `strcmp` is used in an expression, you get a function pointer to that function. But you cannot change "where strcmp points to" because `strcmp` is a function and not a pointer.

C allows conversions between different function pointer types. However, should you try to call a function through a function pointer of incompatible type, you invoke undefined behavior.

```
int (*funcPtr)(void*,void*);
```

is not compatible with `strcmp`, which has the following format:

```
int strcmp(const char *s1, const char *s2);
```

Meaning:

```
funcPtr = (int(*)(void*, void*))strcmp; // this is ok but not very meaningful
funcPtr(); // this is NOT ok, invokes undefined behavior
```

In order to actually call the function `strcmp` through that function pointer, you would have to cast back to the correct type, which is `int (*)(const char*, const char*)`.

Typecasting a function pointer

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