The 36th lesson function and pointer analysis

1. function Type

(1) A function in C has its own particular type , which is determined by the return value , the parameter type , and the number of parameters . such as int add (int i,int j) is of type int (int,int).

(2) renaming a function type by typedef in C language

typedef Type name(parameter list);//as TypeDef int F (INT,INT);

2. Function pointers

(1) A function pointer is used to point to a function, and the function name is the entry address of the execution body.

(2) Two methods for defining function pointers

① is defined by the function type: functype* pointer;

② Direct definition:type(*pointer) (parameter list);

Where type is the return value type , pointer is the function pointer variable name, parameter list is the parameter type

Use of the "instance analysis" function pointer (tip: Jump directly to a fixed address using a function pointer to start execution)

#include <stdio.h>typedefint(FUNC) (int);intTestinti) {    returnIi;}voidf () {printf ("Call f () ... \ n");}intMain () {FUNC* pt = test;//legal, the function name is the entry address of the function body.//directly defines the function pointer, &f is the old-fashioned notation. The function name is just a symbol (not a variable),//As with the array name, no memory is allocated for it, so &f and F are equal in value.     void(*PF) () = &F; //If you know the address of a function, this can be changed to a fixed address value, to achieve jump!  printf ("PF =%p\n", PF); printf ("f =%p\n", F); printf ("&f =%p\n", &f);//The result should be: PF = = f = &f;pf ();//call with a function pointer        (*PF) ();//old-fashioned notationprintf ("Function Pointer call:%d\n", PT (2)); return 0;}

3. Callback function

(1) callback function is a calling mechanism implemented by function pointers

(2) Principle of callback mechanism

① caller does not know the specific function to invoke when a specific event occurs

The ② function does not know when it is called, only the tasks that need to be done

③ when a specific event occurs, the caller invokes the specific function through the function pointer .

(3) The caller and callee in the callback mechanism are not dependent on each other.

Instance analysis callback function using example

#include <stdio.h>typedefint(*weapon) (int);//the function of manipulating a weapon//fight with a boss using some kind of weaponvoidFight (weapon WP,intArg//ARG is the parameter passed to the function pointer{    intresult =0; printf ("Fight boss!\n"); Result= WP (ARG);//call the callback function and pass in the parameter argprintf ("Boss loss:%d\n", result);//How much does boss bleed? }//using weapons--knivesintKnife (intN) {    intRET =0; inti =0;  for(i=0; i< N; i++) {printf ("Knife attack:%d\n",1); RET++; } printf ("\ n"); returnret; }//using weapons-swordsintSwordintN) {    intRET =0; inti =0;  for(i=0; i< N; i++) {printf ("Sword attack:%d\n",5); RET++; } printf ("\ n"); returnret; }//using weapons--gunsintGunintN) {    intRET =0; inti =0;  for(i=0; i< N; i++) {printf ("Gun attack:%d\n",Ten); RET++; } printf ("\ n"); returnret; }intMain () {Fight (knife,3);//cut it 3 times with a knife .Fight (Sword,4);//Stab 4 times with a sword .Fight (Gun,5);//shot 5 times .    return 0;}

4. Summary

(1) There are specific types of functions in the C language

(2) Function pointers can be defined using function types

(3) Function pointer is the key technique to implement callback mechanism

(4) Through the function pointer can be implemented in C program fixed address jump

The 36th lesson function and pointer analysis