What Is Function Pointer

Function Pointer is a variable(a pointer) that holds the address  of another function. Function pointer is a pointer variable, just like a normal pointer. However, function pointer points to the address of the function. In C like all normal variables, functions also will be stored in the memory. So every function will have a valid address. Function pointer will point to this address.


Syntax:



DATA TYPE (*ptr) ();
DATA TYPE (*ptr) (Data Type);


When declaring a function pointer you must declaration the function's return type and the function's parameter type. Example supposes we had two functions.


Void read_emp (emp*e);
  and
Void print_emp(emp*e);


We can declare a variable that could pointer to either of these functions as follows:


void(*func_ptr) (emp*e);


(*func_ptr)  Is the name to the variable, void' is actual variable declaration void(*func-ptr) (emp*e); ,(*func-ptr)  is variable declaration, void * func-ptr(emp*e);


 Upper syntax it will return a void pointer


 (void * func-ptr(emp*e); is the function prototype)

Suppose  you to have third function;

Void print_integer (int x);

It would not be possible to assign func_ptr to pointer to print_integer as they are  different  function types   parameter is  different types.Using the example for the previous.

void(*func_ptr) (emp*e);,we could assign func_ptr to pointer to read_emp as follows,

 Func_ptr=read_emp,note that no  &  is required, note (extremely important) that,Func_ptrr=ead_emp is very different from,Func_ptr=read_emp();

(Func_ptr=read_emp; take  the function  pointer an address and assign to func_ptr variable)

(Func_ptr=read_emp(); is read_emp() run the program and return value is assigned  to func_ptr).Once func_ptr has been initialized.

Func_ptr=read_emp;


We can call the function read_emp via func_ptr, as follows.


  emp e;


 Func_ptr(&e);



  Example

static int add(int a,int b)                {                            return a+b;                 }  static int sub(int x,int y)              {                          return a-b;              }    main()                         {                     int x,y;                     int temp;                     int result;                     int(*func_ptr) (int,int);   // function pointer                     printf("please enter the first number");                    scanf("%d",&x);                     printf("please enter the second number");                    scanf("%d",&y);                    printf("you want to Add or Subb y/n");                   scanf("%c",temp);                   if(temp=='y')||(get char()=='a')                   func_ptr=int add; // pointing to function                   else                   func_ptr=int subb; // pointing to function                  return=func_ptr(x,y);                  printf("%d\n",result); }

Example 2

int fun ptr() {             static int s=10;               ++s;              Returns; } void main() {        int r;        int(*ptr) ();  // function pointer        ptr=funptr;       r=ptr();   //r=funptr();    //r=funptr()       printf("\n valu=%d",r); }

Posted in: C faq