Detailed explanation of the advanced part of C language (advanced pointers 2)

Hello everyone! I quickly wrote the pointer part part 2. See the first part: Detailed explanation of the advanced part of C language (Advanced pointer 1)_In short, it is a very ugly blog-CSDN Blog

For the preliminary part of pointers, see: Detailed explanation of the advanced part of C language (preliminary pointers)_In short, it is a very awkward blog-CSDN Blog 

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1. Function pointer 

1.Explanation and examples 

Function pointer: In C language, function pointer is a pointer variable pointing to a function. It can be stored in memory like other variables, and the corresponding function can be called through a function pointer.

Declare function pointer: returnType (*pointerName)(parameterTypes);

in:

• returnType is the return type of the function.
• pointerName is the name of the function pointer.
• parameterTypes is the parameter type of the function

// 定义一个函数
int add(int a, int b) {
    return a + b;
}

int main()
{
    // 声明一个函数指针
    int (*funcPtr)(int, int);

    // 将函数指针指向add函数
    funcPtr = add;

    // 通过函数指针调用函数
    int result = funcPtr(2, 3);  // 结果为5   平时调用函数时都是函数名（地址），也可以想通
    int result = (*funcPtr)(2, 3);  // 这两种均可以，funcPtr是地址，通过*解引用来找到
    return 0;
}

 2. Two classic pieces of code in "C Traps and Defects"

2.1 ( * ( void  ( * )( ) ) 0 ) ( );

//Code 1 ( * ( void ( * )( ) ) 0 ) ( );

1. void ( * )( ) This is a type declaration of a function pointer. It represents a voidfunction pointer with no parameters and a return type of
2. ( void ( * )( ) ) 0 This is a forced type conversion of 0 into a function pointer type.
3. * ( void ( * )( ) ) 0 dereferences the function address at address 0
4.  ( * ( void ( * )( ) ) 0 ) ( ) call this function

2.2void ( * signal( int , void( * ) ( int ) ) ) (int); 

//代码2 void ( * signal( int , void( * ) ( int ) ) ) (int); 

 

void (*signal(int, void (*)(int)))(int): This is the syntax for a function declaration. It represents signala function that accepts two parameters: a inttype parameter and a pointer to a function that accepts intthe type parameter and returns voidit. This function returns a result pointer to a function that accepts inta type parameter and returnsvoid

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2. Array of function pointers

1.Explanation and examples

Array of function pointers: An array of function pointers is an array in which each element is a function pointer. You can store different function pointers in an array and use them as needed 

 

Declare an array of function pointers: return_type (*array_name[size])(parameter_list); 

1. return_type: The return type of the function pointed to by the function pointer.
2. (*array_name): The name of the function pointer array. It is a pointer to an array.
3. [size]: The size of the function pointer array. It represents the number of function pointers in the array.
4. (parameter_list): The parameter list of the function pointed to by the function pointer

 Compared with function pointers, there is just one more [ ] after the function name.

// 定义函数1
void func1(int num) {
    printf("This is function 1. Number: %d\n", num);
}

// 定义函数2
void func2(int num) {
    printf("This is function 2. Number: %d\n", num);
}

// 定义函数3
void func3(int num) {
    printf("This is function 3. Number: %d\n", num);
}

int main() {
    // 将函数指针赋值给函数指针数组的元素
    void(*pf[3])(int) = { &func1,&func2, &func3 };

    // 调用函数指针数组中的函数
    for (int i = 0; i < 3; i++) {
        pf[i](i);
    }
    return 0;
}

 

2. Use to implement the calculator

 

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 = 1;
    int result = 0;
    int a = 0;
    int b = 0;
    while (input)
    {
        menu();
        printf("请输入:\n");
        scanf("%d", &input);//根据menu来输入数字啦
        int(*pf[5])(int, int) = { NULL,add,sub,mul,div };//第一个是NUll是为了使数字与菜单对应
        if (input >= 1 && input <= 4)
        {
            printf("请输入两个数\n");
            scanf("%d %d", &a, &b);
            result = pf[input](a, b);
            printf("%d\n", result);
        }
        else if(input==0)
        {
            printf("退出计算器");
        }
        else
        {
            printf("输入有误，请重新输入");
        }
    }
    return 0;
}

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3. 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.
 

The syntax for a pointer to an array of function pointers is as follows:

return_type (*(*pointer_name)[size])(parameter_list);

1. return_type: The return type of the function pointed to by the function pointer.
2. (*pointer_name): The name of a pointer to an array of function pointers. It is a pointer to an array of function pointers.
3. [size]: The size of the function pointer array. It represents the number of function pointers in the array.
4. (parameter_list): The parameter list of the function pointed to by the function pointer

Compared with the function pointer array, there is only one more * in front of the name to indicate that it is a pointer.

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4. Callback function

1.Explain 

A 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.

 2. Case study

int add(int x, int y)
{
    return x + y;
}

// 定义一个回调函数
void callback(int result) 
{
    printf("回调函数被调用，结果为：%d\n", result);
}

// 定义一个函数，接受一个函数指针作为参数
void performOperation(int (*operation)(int, int), int a, int b, void (*callback)(int)) 
{
    int result = operation(a, b);
    callback(result);
}

int main()
{
    // 调用函数，并传递回调函数作为参数
    performOperation(add, 2, 3, callback);
	return 0;
}

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 Today’s content ends here first. As expected, the next time will be a more detailed example demonstration and simulation of the callback function.

thanks for your support! !