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A character pointer is a pointer to a character.
#include <stdio.h>
int main()
{
char ch = 'q';
char* p = &ch;
*p = 'a';
return 0;
}
Pointer array is an array used to store pointers
int* arr[10];//整型指针的数组
char* arr[4];//一级字符指针的数组
char** arr[5];//二级字符指针的数组
An array pointer is a pointer that can point to an array
arr represents the address of the first element of the array
&arr represents the address of the array
A function pointer is a pointer to a function
#include <stdio.h>
void text()
{
printf("hehe\n");
}
int main()
{
printf("%p\n", text);
printf("%p\n", &text);
return 0;
}
1. Array of function pointers
In the previous study, we already knew what a pointer array is
A pointer array is an array that stores pointers
int *arr[10];
Store the address of a function in an array, then this array is called a function pointer array
int (*parr1[10])();
Use of function pointer array: transfer table
Example: adder
#include <stdio.h>
void menu()
{
printf("****************************\n");
printf("*** 1. add 2. sub ***\n");
printf("*** 3. mul 4. div ***\n");
printf("*** 0. exit ***\n");
printf("****************************\n");
}
int Add(int x, int y)
{
return x + y;
}
int Sub(int x, int y)
{
return x - y;
}
int Mul(int x, int y)
{
return x * y;
}
int Div(int x, int y)
{
return x / y;
}
int main()
{
int input = 0;
int x = 0;
int y = 0;
int ret = 0;
do
{
menu();
printf("请选择>");
scanf("%d", &input);
switch(input)
{
case 1:
printf("请输入2个操作数");
scanf("%d %d", &x, &y);
ret = Add(x, y);
printf("ret=%d\n", ret);
break;
case 2:
printf("请输入2个操作数");
scanf("%d %d", &x, &y);
ret = Sub(x, y);
printf("ret=%d\n", ret);
break;
case 3:
printf("请输入2个操作数");
scanf("%d %d", &x, &y);
ret = Mul(x, y);
printf("ret=%d\n", ret);
break;
case 4:
printf("请输入2个操作数");
scanf("%d %d", &x, &y);
ret = Div(x, y);
printf("ret=%d\n", ret);
break;
case 0:
printf("退出计算器\n");
break;
default:
printf("输入错误，重新输入\n");
break;
}
} while (input);
return 0;
}
We can also implement this calculator using an array of function pointers:
#include <stdio.h>
void menu()
{
printf("****************************\n");
printf("*** 1. add 2. sub ***\n");
printf("*** 3. mul 4. div ***\n");
printf("*** 0. exit ***\n");
printf("****************************\n");
}
int Add(int x, int y)
{
return x + y;
}
int Sub(int x, int y)
{
return x - y;
}
int Mul(int x, int y)
{
return x * y;
}
int Div(int x, int y)
{
return x / y;
}
int main()
{
int input = 0;
int x = 0;
int y = 0;
int ret = 0;
do
{
menu();
printf("请选择>");
scanf("%d",&input);
int (*pfArr[])(int, int) = {
NULL, Add,Sub,Mul,Div };
if (0 == input)
{
printf("退出计算器\n");
}
else if (input >= 1 && input<= 4)
{
printf("请输入2个操作数");
scanf("%d %d", &x, &y);
ret = pfArr[input](x, y);
printf("ret=%d\n", ret);
}
else
{
printf("选择错误，重新选择\n");
}
}
while (input);
return 0;
}
2. Pointer to function pointer array
A pointer to an array of function pointers is a pointer, a pointer points to an array, and the elements of the array are all function pointers.
int a=10;
int b=20;
int c=30;
int *arr[]={
&a,&b,&c};//这是一个整型指针数组
int* (*p)[3]=&arr;//p是指针，是指向整型指针数组的指针
int (*pfArr[5])(int, int) = {
NULL, Add,Sub,Mul,Div };//pfArr是函数指针数组
int (*(*p)[5])(int ,int )=&pfArr;//p是指针，是指向函数指针数组的指针
3. Callback function
What is a callback function?
The callback function is a function called through a function pointer. If you pass a function pointer (address) as a parameter to another function, and when this pointer is used to call the function it points to, we say it is a callback function. The callback function is not called directly by the implementer of the function, but is called by another party when a specific event or condition occurs to respond to the event or condition
Next we use the callback function to implement the calculator function:
#include <stdio.h>
void menu()
{
printf("****************************\n");
printf("*** 1. add 2. sub ***\n");
printf("*** 3. mul 4. div ***\n");
printf("*** 0. exit ***\n");
printf("****************************\n");
}
int Add(int x, int y)
{
return x + y;
}
int Sub(int x, int y)
{
return x - y;
}
int Mul(int x, int y)
{
return x * y;
}
int Div(int x, int y)
{
return x / y;
}
void calc(int (*pf)(int, int))
{
int x = 0;
int y = 0;
int ret = 0;
printf("请输入2个操作数");
scanf("%d %d", &x, &y);
ret = pf(x, y);
printf("ret=%d\n", ret);
}
int main()
{
int input = 0;
do
{
menu();
printf("请选择>");
scanf("%d", &input);
switch(input)
{
case 1:
calc(Add);
break;
case 2:
calc(Sub);
break;
case 3:
calc(Mul);
break;
case 4:
calc(Div);
break;
case 0:
printf("退出计算器\n");
break;
default:
printf("输入错误，重新输入\n");
break;
}
} while (input);
return 0;
}
Next we are going to use qsort for sorting, but before that we first use bubble sort to sort an integer array in ascending order.
#include <stdio.h>
void print(int arr[], int sz)
{
int i = 0;
for (i = 0; i < sz; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
}
void bubble_sort(int arr[],int sz)
{
int i = 0;
for (i = 0; i < sz; i++)
{
int j = 0;
for (j = 0; j <sz-1-i; j++)
{
if (arr[j] > arr[j + 1])
{
int tmp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = tmp;
}
}
}
}
int main()
{
int arr[] = {
9,8,7,6,5,4,3,2,1,0 };
int sz = sizeof(arr) / sizeof(arr[0]);
print(arr, sz);
bubble_sort(arr, sz);
print(arr, sz);
return 0;
}
The above bubble sorting is only suitable for sorting integer arrays
Before using qsort to sort, we must first understand the qsort function
void qsort(void* base, //待排序数组的第一个元素的地址
size_t num, //待排序数组的元素个数
size_t size,//待排序数组中一个元素的大小
int (* c0mpar)(const void*, const void*)//函数指针-compar指向了一个函数，这个函数是用来比较两个元素的
//1. 排序整型数组, 两个整型可以直接使用>比较
//2. 排序结构体数组，两个结构体的数据不能直接使用>比较也就是不同类型的数据，比较出大小，方法是有差异的
//void* 类型的指针不能进行解引用操作符，也不能进行+-整数的操作
//void* 类型的指针是用来存放任意类型数据的地址
//void* 无具体类型的指针
#include <stdio.h>
#include <stdlib.h>
void print(int arr[], int sz)
{
int i = 0;
for (i = 0; i < sz; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
}
int cmp_int(const void* e1, const void* e2)//e1和e2中存放的是需要比较的两个元素的地址
{
return *(int*)e1 - *(int*)e2;
}
//qsort排序整型数据
void text1()
{
int arr[] = {
9,8,7,6,5,4,3,2,1,0 };
int sz = sizeof(arr) / sizeof(arr[0]);
print(arr, sz);
qsort(arr, sz, sizeof(arr[0]), cmp_int);
print(arr, sz);
}
int main()
{
text1();
return 0;
}
qsort sorting structure
Sort by age
#include <stdio.h>
#include <stdlib.h>
struct Stu
{
char name[20];
int age;
};
int age(const void* e1, const void* e2)
{
return((struct Stu*)e1)->age - ((struct Stu*)e2)->age;
}
void text2()
{
struct Stu arr[] = {
{
"zhangsan",24},{
"lisi",16},{
"wangwu",30} };
int sz = sizeof(arr) / sizeof(arr[0]);
qsort(arr, sz, sizeof(arr[0]), age);
}
int main()
{
text2();
return 0;
}
Sort by name
struct Stu
{
char name[20];
int age;
};
int name(const void* e1, const void* e2)
{
return strcmp(((struct Stu*)e1)->name, ((struct Stu*)e2)->name);
}
void text3()
{
struct Stu arr[] = {
{
"zhangsan",24},{
"lisi",16},{
"wangwu",30} };
int sz = sizeof(arr) / sizeof(arr[0]);
qsort(arr, sz, sizeof(arr[0]), name);
}
int main()
{
text3();
return 0;
}