Contents of this article:
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- 1. Understanding of two-dimensional arrays
- (1) Understanding of two-dimensional array array[i] and array[i][j]
- (2) Understanding of array[i]+j, *array[i]+j
- (3) Understanding of the two-dimensional array name array
- 2. Various "forms" of pointers
- (1) Array pointer
- (2) Function pointer
- 3. "Stupidly unclear" about arrays, pointers and functions
- (1) Pointer array
- (2) Function pointer array
- (3) Pointer function
- (4) Definitions of various "demons" (classic written test questions):
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1. Understanding of two-dimensional arrays
(1) Understanding of two-dimensional array array[i] and array[i][j]
- Two-dimensional array: essentially an array with arrays as array elements, that is, an "array of arrays". Also called a matrix, when the number of rows and columns is equal, it is called a square matrix.
- array[i]: represents the address (address, address, address) of the one-dimensional array in the i-th row of the two-dimensional array.
- array[i] [j]: represents the value of the element in row i and column j of the two-dimensional array.
#include <stdio.h>
int main() {
int array[3][4] = {
{
1,2,3,4},
{
5,6,7,8},
{
9,10,11,12},
};
/* 1.array[i]是每一行的数组（一维）的地址 */
int i,j;
for(i=0;i<3;i++){
printf("%p\n",array[i]);
}
/* 2.array[i][j]是每一行数组（一维）的值 */
for(i=0;i<3;i++){
for(j=0;j<4;j++){
printf("%d ",array[i][j]);
}
putchar('\n');
}
return 0;
}
(2) Understanding of array[i]+j, *array[i]+j
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array[i]+j: The address of the i-th row and j-th column of the two-dimensional array
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*array[i]+j: The value of the address of the i-th row and j-th column of the two-dimensional array
注意:*array[i]+j和*（array[i]+j）写法不同，表示意思相同
#include <stdio.h>
int main() {
int array[3][4] = {
{
1,2,3,4},
{
5,6,7,8},
{
9,10,11,12},
};
/* 1.array[i]+j:二维数组的i行第j列的地址 */
/* 2.*array[i]+j:二维数组第i行第j列的地址的值（元素的值） */
/* PS：*array[i]+j和*(array[i]+j)意思一样(*和+运算符优先级一样，遵循从右往左计算) */
int i,j;
for(i=0;i<3;i++){
for(j=0;j<4;j++){
printf("%d\t",*array[i]+j);
}
putchar('\n');
}
return 0;
}
(3) Understanding of the two-dimensional array name array
在前面一维数组的认知中，我们知道数组名就是数组的首地址，可以通过数组首地址来操作数组元素。同样地，在二维数组中，二维数组名array也表示二维数组的首地址，只是该地址存放的是每一组一维数组的首地址。也就是说，二维数组名是一个存放其一维数组首地址的地址（"地址的地址"）。所以array[i]也可以写成*（array+i)；array[i]+j可以写成(*(array+i))+j；可以理解成以array为基地址，*(array+i)偏移i得到第i行的首地址，(*(array+i))+j再偏移j得到第i行第j列元素的地址；或许有亿点点绕，亿点点晕，继续体会下面的代码吧
- Array: Two-dimensional array name, which is the address that stores the first address of its one-dimensional array (although the two-dimensional array name is somewhat similar to the second-level pointer in understanding, the two-dimensional array name is not different from the second-level pointer)
#include <stdio.h>
int main() {
int array[3][4] = {
{
1,2,3,4},
{
5,6,7,8},
{
9,10,11,12},
};
int i,j;
for(i=0;i<3;i++){
for(j=0;j<4;j++){
printf("%d\t",*array[i]+j); //写法一
printf("%d\t",*(*(array+i))+j); //写法二（输出结果可以看到，两种写法等价）
}
putchar('\n');
}
return 0;
}
2. Various "forms" of pointers
(1) Array pointer
-
Array pointer: A pointer to an array, that is, the address pointing to the first address of the array. (In fact, it is similar to the array mentioned above)
-
int (*p)[4] = array (array is the name of a two-dimensional array): Define a pointer variable pointing to the first address of a two-dimensional array with four elements.
（二维数组实质上同一维数组一样，在内存中的地址空间连续，可以通过指针进行操作） -
Output the specified row and column elements in the two-dimensional array according to the row and column values input by the user, which requires the use of array pointers.
#include <stdio.h>
void getInput(int *i,int *j){
printf("请输入行、列值(从1开始):");
scanf_s("%d %d",i,j);
printf("input done\n");
}
int findTargetValue(int (*p)[4],int i,int j){
int targetValue;
// targetValue = p[i][j];
targetValue = *(*(p+i))+j;
return targetValue;
}
int main() {
int array[3][4] = {
{
1,2,3,4},
{
5,6,7,8},
{
9,10,11,12},
};
int i,j;
int targetValue;
getInput(&i,&j);
targetValue = findTargetValue(array,i-1,j-1);
printf("矩阵%d行%d列的数据是:%d",i,j,targetValue);
return 0;
}
(2) Function pointer
【2-1】Understanding of function pointers
- Function pointer: A pointer to a function, a pointer variable that stores the address of the function.
- Definition: int (*p)(const char *format, …);
- Assignment (initialization so that it points to a function - the function name is also the address): p = printf;
- Call: (*p)(“Hello World”);
#include <stdio.h>
int main() {
int (*p)(const char *format, ...) = printf;
(*p)("Hello World\n");
return 0;
}
【2-2】Application of function pointers
- Application: According to different situations during program running, different functions are called (similar to the interface in Java) +
- Example: There are two integers a and b. The user inputs 1, 2 or 3. If you input 1, the program will give the larger of a and b. If you input 2, it will give the smaller of a or b. If you input 3, it will find a and b. of and.
#include <stdio.h>
#include <stdlib.h>
int getMax(int data1,int data2){
return data1>data2 ? data1:data2;
}
int getMin(int data1,int data2){
return data1<data2 ? data1:data2;
}
int getSum(int data1,int data2){
return (data1+data2);
}
int getCommandAndHandle(int data1,int data2,int (*p)(int, int)){
int choise = 0;
printf("请输入1-取大值、2-取小值、3-求和:\n");
scanf_s("%d",&choise);
switch (choise) {
case 1:
p = getMax;
break;
case 2:
p = getMin;
break;
case 3:
p = getSum;
break;
default:
printf("error\n");
exit(-1);
}
return (*p)(data2,data1);
}
int main() {
int data1 = 10;
int data2 = 20;
int result;
int (*command)(int, int) = NULL;
result = getCommandAndHandle(data1,data2,command);
printf("%d\n",result);
return 0;
}
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Linux thread creation function: int pthread_create(pthread_t *th, const pthread_attr_t *attr, void ( func)(void *), void *arg);
And the underlying logic of C++ QT's signal and slot callback functions - function pointer implementation.
3. "Stupidly unclear" about arrays, pointers and functions
(1) Pointer array
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Pointer array: An array whose elements are all pointer type variables is called a pointer array (① is an array; ② array elements are pointers)
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How to define: a pointer array with 4 integer variable elements: int *p[4]
区别前面的数组指针int (*p)[4],可以知道优先级[]比*高
(2) Function pointer array
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Array of function pointers: ① is an array; ② array elements are pointers; ③ pointers point to the address of the function
-
How to define: int (*p[4])(int,int)
优先级：() > [] > *；到了这里，优先级对理解记忆这些东西显得十分关键 -
Example: Pass in two values and output the maximum value, minimum value and the sum of the two numbers (array of function pointers).
#include <stdio.h>
int getMax(int data1,int data2){
return data1>data2 ? data1:data2;
}
int getMin(int data1,int data2){
return data1<data2 ? data1:data2;
}
int getSum(int data1,int data2){
return (data1+data2);
}
void getAllResult(int data1,int data2,int (*p[3])(int,int)){
printf("Max Min Sum\n");
for(int i=0;i<3;i++){
printf("%d ",(*p[i])(data1,data2));
}
}
int main() {
//函数指针
//int (*p)(int,int);
//函数指针数组
int (*p[3])(int,int) = {
getMax, getMin, getSum};
getAllResult(88,99,p);
return 0;
}
(3) Pointer function
- Pointer function: a function whose return value is a pointer type (① is a function; ② the function return value is a pointer)
- Definition: int *p(int i,int j)
- Outputs the elements of a column of a given two-dimensional array (matrix) based on a user-specified row number.
#include <stdio.h>
int *findTargetSubArray(int (*parray)[4],int target){
return (int *)parray+target;
}
int main() {
int array[3][4] = {
{
11,22,33,44},
{
55,66,77,88},
{
99,110,220,330},
};
int targetNumber;
int *subArray;
puts("输入要查询的行号（0-2）");
scanf_s("%d",&targetNumber);
subArray = findTargetSubArray(array,targetNumber);
for (int i = 0; i < 4; i++) {
printf("%d ",*subArray++);
}
}
(4) Definitions of various "demons" (classic written test questions):
- It is recommended to copy it to the IDE and practice it.
1. Define an integer
2. Define a pointer to an integer
3. Define a pointer to a pointer that points to an integer
4. Define an array of 10 integers
5. Definition An array of 10 pointers, each pointing to an integer.
6. Define a pointer to an array of 10 integers.
7. Define a pointer to a pointer. The pointed pointer points to an array of 10 integers. Array of type
8. Define a pointer to the array, there are 10 integer pointers in the array
9. Define a pointer to the function, the function has only one integer parameter and returns an integer
10. Define a pointer with 10 An array of pointers. Each array points to a function. The function has only one integer parameter and returns an integer. 11.
Define a function pointer. The function pointed to has two integer parameters and returns a function pointer. The returned function pointer Pointer to a function that takes an integer parameter and returns an integer
定义一个整型数 int a;
定义一个指向整型数的指针 int *a;
定义一个指向指针的指针，它指向的指针指向一个整型数 int **a;
定义一个有10个整型数的数组 int a[10];
定义一个有10个指针的数组，每个指针指向一个整型数 int *p[10];
定义一个指向有10个整型数的数组的指针 int (*p)[10];
定义一个指向指针的指针，被指向的指针指向一个有10个整型数的数组 int *(*p)[10];(错) / int (**a)[10];（对）
定义一个指向数组的指针，数组中有10个整型指针 int *((*p1)[10]);(我的答案) / int *(*p2)[10];（参考答案）
定义一个指向函数的指针，该函数只有一个整型参数且返回一个整型数 int (*p)(int);
定义一个有10个指针的数组，每个数组指向一个函数，该函数只有一个整型参数且返回一个整型数 int (*p[10])(int);
定义一个函数指针，指向的函数有两个整型参数且返回一个函数指针，返回的函数指针指向有一个整型参数且返回整型数的函数 int(* (*p)(int,int))(int)
- Regarding question 8: I really don’t understand question 8. I still think int *(( *p1)[10]); and int *( *p2)[10]; are the same. I hope someone can shed some light on this!
