C：函数指针、回调函数

函数指针

 是一个指针，指向函数的指针，指针存放的都是地址，所以函数指针存放的是函数的地址。数组名就是数组的首地址，函数名就是函数的首地址。与数组类似。

代码demo

   int (*p) (int ,int ) = NULL;

// int (*) (int ,int )   这就是指针变量的类型  (除了函数名)
    p = maxValue;   指针变量存储的是函数的地址（函数名）

//    定义一个有两个整形参数且返回为整型的函数指针

#import <Foundation/Foundation.h>

//    求两个数字的最大值
//    函数的类型就是由 返回值类型 + 参数个数及类型
int maxValue(int , int );
int maxValue(int a , int b ){
    return a > b ? a :b ;
}
int minValue(int ,int );
int minValue(int a, int b){
    return a < b ? a : b;
}
//char getString(); 不能这样写
char *getString();//类型 char *     函数名  getString  返回值类型为 char * 而且没有参数的函数
char *getString(){
//    char a[10] = "hello";
    char *a = "hello";
    return a;
}

void outputNumber(int a); // 类型 void （）
void outputNumber(int a){//void * 是一个泛型 返回泛型的指针 ？？？
    printf("
outputNumber 输出传入数字 %d	",a);
}


//    定义一个函数求两个浮点数的和
float requireTwoFloatSum(float a, float b);
float requireTwoFloatSum(float a, float b){
    return a + b;
}
int main(int argc, const char * argv[]) {
   
    
//    定义一个有两个整形参数且返回为整型的函数指针
    int (*p) (int ,int ) = NULL;
// int (*) (int ,int )   这就是指针变量的类型 (除了函数名)
    p = maxValue; // 指针变量存储的是函数的地址（函数名）
    int value = p (20,30);
    printf("
value = %d 	",value);
    int (*p0) (int , int ) = NULL;
    p0 = minValue;
    int min = p0(6 , 7);
    printf("
 min = %d
",min);
    
    
// 分别定义函数指针，来指向对应的函数，然后使用此指针实现函数的调用
//    char (*p1) = NULL;
//    p1 = getString;
    char * str = getString();//没有参数小括号 不能省略
//    练习：分别定义函数指针，来指向对应的函数，然后使用此指针实现函数的调用
    char *(*p1)() = NULL; //第二个 * 是标记 p1 是一个指针    p1的类型是char *(* )()
    printf("%s	",str);
    
    
    // outputNumber 输出传入数字
    int (*p2)(int) = NULL;
    p2 = outputNumber;
    p2(2);
    
    
//    定义一个函数求两个浮点数的和
    float (*p3)(float ,float) = NULL;
    p3 = requireTwoFloatSum;
    float a = p3(15.44,14.33);
    printf("
定义一个函数求两个浮点数的和 %.2f",a);
    return 0;
}

#import <Foundation/Foundation.h>

//    定义一个函数求两个整数的和
int requireTwoSum(int a, int b);
int requireTwoSum(int a, int b){
    return a + b;
}

//    求两个数字的最大值
int maxValue(int , int );
int maxValue(int a , int b ){
    return a > b ? a :b ;
}
//    求两个数字的最小值
int minValue(int ,int );
int minValue(int a, int b){
    return a < b ? a : b;
}

//函数当成一个函数形参
typedef int (*FUNCTION)(int ,int); //如果这里不写 typedef 的话，    typedef FUNCTION f;这句就要报错 ，typedef 只是为数据类型重命名
//这个 FUNCTION 可以指向任意一个  int (* )(int ,int) 这种类型的函数（上面的求和，求最大值，求最小值）
typedef FUNCTION f;
int getValue(int ,int ,f );//声明了一个可以传递函数的函数
int getValue(int a ,int b ,f f1 ){
    int q = f1(a,b);
    return q;
}

int main(int argc, const char * argv[]) {
   
    int arr = getValue(4, 8, maxValue);
    printf("maxValue = %d	",arr);
    int brr = getValue(23, 3, minValue);
    printf("minValue = % d	",brr);
    int crr = getValue(29, 76, requireTwoSum);
    printf("TwoSum = %d	",crr);
    
    
    return 0;
}

  typedef 给结构体 与 指针函数 定义新的名字的时候，要注意  把新名字存放正确的地方。typedef 只是给数据类型重新定义名字

应用实战

#import <Foundation/Foundation.h>
#import "runSort.h"
#import "teacher.h"

int main(int argc, const char * argv[]) {
    /*
    Student stu[5] ={
        {"zhang san", 12 , 89},
        {"li si", 15 , 98},
        {"wang wu", 45 , 78},
        {"liu guang dan ", 18, 45},
        {"hei li qi", 11, 49}
    };
    match fun[3] = {
        {compaerByAge,"age"},
        {compaerByName,"name"},
        {compaerByScore,"score"}
    };
    compareMethood pp = getFunction(fun, 2, "name");
    sortArrAccending(stu, 5 ,pp);
     */
    Teacher teacher[5]={
        {"wang ma zi",'m',12,101,8.9},
        {"li si",'m',48,102,9.6},
        {"huang xing",'f',45,110,4.9},
        {"zhang ming",'f',46,106,10},
        {"zhang san",'f',23,109,7.5}

    };
    match2 fun2[6]={
        {compareNameByAscending,"namesx"},
        {compareNmaeByDescending,"namejx"},
        {compareNumByAscending,"numsx"},
        {compareNumByDescending,"numjx"},
        {compareMarkByAscending,"marksx"},
        {compareMarkByDescending,"marksx"},
    };
    compareMethood2 p2 = getFounction(fun2, 6, "numsx");
    sortTeachers(teacher,5,p2);

    return 0;
}

#import <Foundation/Foundation.h>

typedef struct teacher{
    char name[20];
    char gender;
    int  age;
    int  num;
    float mark;
}Teacher;
//指针函数（对比下面好多升序降序的函数）
typedef BOOL (* compareMethood2)(Teacher teacher1,Teacher teacher2) ;
typedef struct Match2{
    compareMethood2 Function2;
    char fname2[20];
}match2;

//打印 teacher 信息
void  printTeacher(Teacher *  teacher);
//函数指针类型
typedef BOOL(*compareFunctionPointer)(Teacher teacher1,Teacher teacher2);
//老师数组排序函数
void sortTeachers(Teacher *teacher,int count ,compareFunctionPointer cfp);
//声明一个打印数组中所有老师的函数
void printTeachers(Teacher *teachers,int count);
//两个比较姓名的函数 升序
BOOL compareNameByAscending(Teacher teacher1, Teacher teacher2);
//降序
BOOL compareNmaeByDescending(Teacher teacher1, Teacher teacher2);
//分别声明两个比较Teacher员工编号的函数 升序
BOOL compareNumByAscending(Teacher taecher1, Teacher teacher2);
//降序
BOOL compareNumByDescending(Teacher teacher1,Teacher teacher2);
//分别声明两个比较Teacher员工评分的函数 升序
BOOL compareMarkByAscending(Teacher teacher1,Teacher teacher2);
//降序
BOOL compareMarkByDescending(Teacher teacher1,Teacher teacher2);
//声明一个输出教师数组中全部男老师的函数
void printMaleTeacher(Teacher *teacher,int count);
//声明一个输出教师数组中全部女老师的函数
void printFemaleTeacher(Teacher *teacher,int count);
//条件匹配函数
compareMethood2 getFounction(match2 * match2, int count ,char * frame2);

#import "teacher.h"

//打印 teacher 信息
void  printTeacher(Teacher * teacher){
    printf("姓名: %s 性别: %c 年龄: %d 工号: %d 评分: %.2f 
",teacher->name,teacher->gender,teacher->age,teacher->num,teacher->mark);
}
//老师数组排序函数
void sortTeachers(Teacher *teacher,int count ,compareFunctionPointer cfp){
    if (cfp == NULL) {
        printf("没有匹配");
    }else{
        for (int i = 0; i < count - 1; i++) {
            for (int j = 0; j < count - 1 - i; j++) {
                if (cfp(*(teacher + j),*(teacher + j + 1))) {
                    Teacher temp = *(teacher + j);
                    *(teacher + j) = *(teacher + j + 1);
                    *(teacher + j + 1) = temp;
                }
            }
        }
    }
    printTeachers(teacher ,count);
}
//声明一个打印数组中所有老师的函数
void printTeachers(Teacher *teachers,int count){
    for (int i = 0; i < count ; i++) {
        printf("姓名: %s 性别: %c 年龄: %d 工号: %d 评分: %.2f 
",(teachers + i)->name,(teachers + i)->gender,(teachers + i)->age,(teachers + i)->num,(teachers + i)->mark);
    }
}
//两个比较姓名的函数 升序
BOOL compareNameByAscending(Teacher teacher1, Teacher teacher2){
    return strcmp(teacher1.name,teacher2.name);
}
//降序
BOOL compareNmaeByDescending(Teacher teacher1, Teacher teacher2){
    return strcmp(teacher2.name, teacher1 .name);
}
//分别声明两个比较Teacher员工编号的函数 升序
BOOL compareNumByAscending(Teacher teacher1, Teacher teacher2){
    return teacher1.num > teacher2.num;
}
//降序
BOOL compareNumByDescending(Teacher teacher1,Teacher teacher2){
    return teacher2.num > teacher1.num;
}
//分别声明两个比较Teacher员工评分的函数 升序
BOOL compareMarkByAscending(Teacher teacher1,Teacher teacher2){
    return teacher1.mark > teacher2.mark;
}
//降序
BOOL compareMarkByDescending(Teacher teacher1,Teacher teacher2){
    return teacher2.mark > teacher1.mark;
}
//声明一个输出教师数组中全部男老师的函数
void printMaleTeacher(Teacher *teacher,int count){
    for (int i = 0; i < count; i++) {
        if ((teacher + i)->gender == 'm') {
            printTeacher((teacher + i));
        }
    }
}
//声明一个输出教师数组中全部女老师的函数
void printFemaleTeacher(Teacher *teacher,int count){
    for (int i = 0; i < count; i++) {
        if ((teacher + i)->gender == 'f') {
            printTeacher((teacher + i));
        }
    }
}
//条件匹配函数
compareMethood2 getFounction(match2 * match2, int count, char *fname2){
    for (int i = 0; i < count; i++) {
        if (strcmp(match2[i].Function2, fname2)) {
            return match2[i].Function2;
            break;
        }else{
             return NULL;
        }
    }
    return 0;
}

#import <Foundation/Foundation.h>

typedef struct{//学生信息
    char name[20];
    int  age;
    float score;
}Student;
typedef BOOL(*compareMethood)(Student,Student);
typedef struct Match{
    compareMethood Function ;
    char fname[20];
}match;
//打印学生信息
void outputAllStuInfo(Student *stu,int count);
//升序排序信息
void sortArrAccending(Student *stu,int count ,compareMethood Condition);
//比较两者年龄
BOOL compaerByAge(Student stu1, Student stu2);
//比较两者成绩
BOOL compaerByScore(Student stu1,Student stu2);
//比较两者姓名
BOOL compaerByName(Student stu1,Student stu2);
//条件匹配函数
compareMethood getFunction(match * match ,int count , char *Fname);

#import "runSort.h"

//打印学生信息
void outputAllStuInfo(Student *stu,int count){
    for (int i = 0; i < count; i++) {
        printf("name = %s ,age = %d score = %.2f
",(stu  + i)->name,(stu + i)->age,(stu + i)->score);
    }
}

//升序排序信息
void sortArrAccending(Student *stu,int count,compareMethood Condition){
    if (Condition == NULL) {
        printf("没有匹配");
    }else{
        for (int i = 0; i < count - 1 ; i++) {
            for (int j = 0;j < count - 1 - i; j++) {
                if (Condition(*(stu + j),*(stu + j + 1))) {
                    Student temp = *(stu + j);
                    *(stu + j ) =   *(stu + j + 1);
                    *(stu + j + 1) = temp;
                }
            }
        }
    }
    outputAllStuInfo(stu, 5);
}

//比较两者年龄
BOOL compaerByAge(Student stu1, Student stu2){
    return stu1.age > stu2.age;
}

//比较两者成绩
BOOL compaerByScore(Student stu1,Student stu2){
    return stu1.score > stu2.score;
}

//比较两者姓名
BOOL compaerByName(Student stu1,Student stu2){
    return strcmp(stu1.name ,stu2.name);
}

//条件匹配函数
compareMethood getFunction(match * match ,int count , char *Fname){
    for (int i = 0; i < count; i++) {
        if (strcmp( match[i].Function , Fname)) {
            return match[i].Function;
        }else{
            return NULL;
        }
    }
    return 0;
}