Function pointer, function pointer Definition

Function pointer, function pointer Definition
1. function pointer 1.1 function pointer:

Definition: pointer to a function. You can call the pointer to a function through the function pointer.

The pointer type must be the same as the data type to be pointed to. functions include: list of parameters of the return value function name.
Function pointer Declaration: Return Value Type (* function pointer name) (parameter list) = function name

The function name is the same as the array name.
// Example 1: int (* p) (int a, int B) = sumValue; // sumValue is a simple sum function of two numbers. // The variable name after * must be enclosed in parentheses printf ("% d \ n", p (5, 8 )); // result: 5 + 8 = 13 // Example 2. define a function to print "Hello" void (* p) () = printHello ;//The preceding figure is void.This is just a simple definition of p (); // function pointer call // example 3. define two functions, one for the least value, one for the sum, and the other for the maximum value of 3, 5 or char input [] = {0 }; scanf ("% s", input); int (* p) (int a, int B) = NULL; if (strcmp ("sumValue", input) = 0) {p = sumValue;} else if (strcmp ("maxValue", input) = 0) p = maxValue; printf ("% d", p (3, 5 )); // The result is correct. You can test it yourself.
 

1.2 callback function:

Callback Function Process: A bit similar to function nesting, but the callback function's parameter value is a function pointer. Through the function pointer, the corresponding function is called, and then the function pointer is returned.
For example, write a function to search for students with a score of 90 or higher and add "Gao fushuai" to the name using the callback function"
Student. h:
#import <Foundation/Foundation.h>typedef struct student{    char name[10];    float score;}Student;void search(Student *stu, void (*p) (Student *s));void addString(Student *s);

Student. m:
# Import "Student. h "void search (Student * stu, void (* p) (Student *) {if (stu-> score >=90) {p (stu );}} void addString (Student * s) {strcat (s-> name, "Gao fushuai ");}
 

Main. m:
int main(){    Student stu[3] = {{"zheng", 89}, {"chen", 91}, {"fang", 94}};    for (int i = 0; i < 3; i++) {        search(stu+ i, addString);        printf("%s   %.1f\n", stu[i].name, stu[i].score);    }    return 0;}
 

Result printing:
Zheng 89w.chen Gao fushuai 91.0fang Gao fushuai 94.0 Program ended with exit code: 0
 

1.3 dynamic sorting:

# Import <Foundation/Foundation. h> typedef struct student {char name [20]; int age; float score;} Student;# Pragma mark --------------- General Bubble Sorting START --------------------// Student name Ascending Order -------------------------------- void sortOfName (Student * stu, int count) {for (int I = 0; I <count-1; I ++) {for (int j = 0; j <count-1-I; j ++) {if (strcmp (stu [j]. name, stu [j + 1]. name)> 0) {Student temp = stu [j]; stu [j] = stu [j + 1]; stu [j + 1] = temp ;}}} for (int I = 0; I <count; I ++) {printf ("% s, % d, %. 1f \ n ", stu [I]. name, stu [I]. age, stu [I]. score) ;}}// age descending order ------------------------------ void sortOfAge (Student * stu, int count) {for (int I = 0; I <count-1; I ++) {for (int j = 0; j <count-1-I; j ++) {if (stu [j]. age <stu [j + 1]. age) {Student temp = stu [j]; stu [j] = stu [j + 1]; stu [j + 1] = temp ;}}} for (int I = 0; I <count; I ++) {printf ("% s, % d, %. 1f \ n ", stu [I]. name, stu [I]. age, stu [I]. score) ;}}// score in ascending order --------------------------------- void sortOfScore (Student * stu, int count) {for (int I = 0; I <count-1; I ++) {for (int j = 0; j <count-1-I; j ++) {if (stu [j]. score> stu [j + 1]. score) {Student temp = stu [j]; stu [j] = stu [j + 1]; stu [j + 1] = temp ;}}} for (int I = 0; I <count; I ++) {printf ("% s, % d, %. 1f \ n ", stu [I]. name, stu [I]. age, stu [I]. score );}}// ---------------------------------- END -------------------------------- # pragma mark --------------------- dynamic sorting START ---------------------------// Compare the size of the two age groups. The BOOL compareAge (Student * s1, Student * s2) {return s1-> age> s2-> age;} // compare the size of the two scores, in descending order, BOOL compareScore (Student * s1, Student * s2) {return s1-> score <s2-> score;} // sort BOOL compareName (Student * s1, student * s2) {return strcmp (s1-> name, s2-> name)> 0;} // compare two ages, descending order BOOL compareAge2 (Student * s1, student * s2) {return s1-> age <s2-> age;} typedef BOOL (* PFUN) (Student *, Student *); // PFUN = BOOL (*) (Student, Student)// Name the function pointer type PFUNVoid sortStudent (Student stus [], int count, PFUN pfun) {// This pfun can point to your own encapsulated sorting methods for (int I = 0; I <count-1; I ++) {for (int j = 0; j <count-1-I; j ++) {if (pfun (stus + j, stus + j + 1) = YES) {// call the sort method Student temp = stus [j]; stus [j] = stus [j + 1]; stus [j + 1] = temp ;}}for (int I = 0; I <count; I ++) {printf ("% s, % d, %. 1f \ n ", stus [I]. name, stus [I]. age, stus [I]. score) ;}} int main () {Student stu [5] = {"zhang", 23, 78}, {"zhao", 11, 89 }, {"bala", 22, 78.5 },{ "mouse", 7, 89 },{ "cat", 4,100 }}; // sortOfName (stu, 5 ); // sortOfAge (stu, 5); // sortOfScore (stu, 5); PFUN p = compareAge2; sortStudent (stu, 5, p ); // ------------------------------------- END -------------------------- return 0 ;}
 

1.4 function pointer:

Functions implemented by the Code: input any string of maxValue, minValue, addValue, and subtractValue to implement the functions of the corresponding code:
# Import <Foundation/Foundation. h> // four functions are used to obtain the maximum value, minimum value, sum, and int maxValue (int a, int B) {return a> B? A: B;} int minValue (int a, int B) {return a <B? A: B;} int addValue (int a, int B) {return a + B;} int subtractValue (int a, int B) {return a-B ;} typedef int (* PFUN) (int, int); // function pointer PFUNtypedef struct functionp {// struct, member: name: used to store the name of the corresponding function, func: store the address of the corresponding function char name [20]; PFUN func; // function pointer} Functionp; PFUN getFunctionByName (Functionp func [], int count, char funName []) {// string of the parameter struct array func [count], function string for (int I = 0; I <count; I ++) {if (strcmp (funName, func [I]. name) = 0) {// find the function pointer return func [I] in the corresponding struct. func ;}} return NULL;} int main () {Functionp f [4] ={{ "maxValue", maxValue}, // function string and function pointer {"minValue ", minValue },{ "addValue", addValue },{ "subtractValue", subtractValue }}; while (1) {char name [30] = {0 }; // The function string printf ("Input Function string: \ n"); scanf ("% s", name); getchar (); PFUN fun1 = NULL; // an empty function pointer fun1 = getFunctionByName (f, 4, name); if (fun1 = NULL) {printf ("please input again \ n ");} else printf ("% s = % d \ n", name, fun1 (3, 5);} return 0 ;}
 
Result:
Input Function string:
MaxValue
MaxValue = 5
Input Function string:
AddValue
AddValue = 8
Input Function string:
SubtractValue
SubtractValue =-2
Input Function string: