How can we rename a function in c?

Question

Used the sizeof of function, which gives 1; why?
I want to know the size of the entire function. How to achive it?

#include <stdio.h>
void (*p)(int); 
void test_func(int data)
{
  printf("%d\n",data);
}

main(void)
{
    p = test_func;
    (*p)(4);
    printf("%d",sizeof(test_func));
}

Answer 1

Its simple, as per what I understand.

1. Open your .c file 
2. goto the function which you want to rename,
3. rename it with the new name,
4. replace the new name, where ever this fucntion previously called.

Answer 2

Agree with Arshad, not sure what is the meaning of change the name of function but if you are looking a function to be identified with two names then try typedef.