Contract-type constants, function pointers, callback functions

The definition of a contractual const object does not use the Const keyword, but is considered a const object, for example:

void ReadValue (constint& num) {    << num;} int Main (void) {    int0;    ReadValue (n);   // at this point n is considered a contractual constant }

A function pointer is a pointer to a function, declared as follows:

void (*FUNCP) (int  x); void (*FUNCP) (int);  // two different forms are available

A small example of a function pointer:

//function Pointers#include <stdio.h>void(*FUNCP) ();voidFilefunc ();voidEditfunc ();intMain () {FUNCP=Filefunc; (*FUNCP)    (); FUNCP=Editfunc; (*FUNCP)    (); return 0;}voidFilefunc () {printf ("filefunc\n");}voidEditfunc () {printf ("editfunc\n");}

The callback function is a kind of function which has the user's own definition and the operating system calls, and the callback function is usually implemented by the function pointer.

//callback function#include <stdio.h>//Defining callback FunctionsvoidFilefunc (intTime ) {printf ("filefunc--%d\n", time);}//implementation of callback functionvoidCallbackintTimesvoid(*print) (int)){    inti;  for(i =0; I < times; i++) {print (i); }}voidMainvoid) {Callback (2, Filefunc);}

Contract-type constants, function pointers, callback functions