- Character pointer
- Array pointer
- Pointer array
- Array parameter passing and pointer parameter passing
- Function pointer
- Function pointer array
- Pointer to array of function pointers
- Callback function
- Pointer and array analysis of interview questions
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Character pointer
- One of the pointer types is character pointer char*
- General use
char* p="abcde"; //Constant string, cannot be changed //The starting address of the stored string p is The exact way of writing is plus const modification const char* p="abcde";
Face to face questions:
int main()
{
char arr1[] = "abcdef";
char arr2[] = "abcdef";
const char* p1 = "abcdef";
const char* p2 = "abcdef"; //P1 and P2 have the same address
if (arr1 == arr2)
{
printf("hehe\n");
}
else
{
printf("haha\n");
}
if (p1 == p2)
{
printf("hehe\n");
}
else
{
printf("haha\n");
}
return 0;
}-
Array pointer
- Is a pointer that can point to the array. It is used to store the address of the array. Int (* P) [n] = & arr; *p==arr
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char* parr[5]; char* (*pa)[5] = &parr;
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Basic usage;
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#include <stdio.h> //Parameters are arrays void print1(int arr[3][5],int x,int y) { int i = 0; int j = 0; for (i = 0; i < x; i++) { for (j = 0; j < y; j++) { printf("%d ", arr[i][j]); } printf("\n"); } } //Parameters are pointers void print2(int(*p)[5], int x, int y) { int i = 0; for (i = 0; i < x; i++) { int j = 0; for (j = 0; j < y; j++) { //arr[i] == *(arr+i) == *(p+i) == p[i] //*(p+i) == p[i] *(p[i]+j) == p[i][j] printf("%d ", *(*(p + i)+j)); } printf("\n"); } } int main() { int arr[3][5] = { {1,2,3,4,5},{2,3,4,5,6},{3,4,5,6,7} }; print1(arr, 3, 5);//The address of the first row of the first element address of the arr array name print2(arr, 3, 5); return 0; }
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Pointer array
- Is an array used to store pointers
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#include <stdio.h> int main() { int i = 0; int j = 0; int arr1[] = { 1,2,3,4,5 }; int arr2[] = { 2,3,4,5,6 }; int arr3[] = { 3,4,5,6,7 }; int* arr[] = { arr1,arr2,arr3 }; for (i = 0; i < 3; i++) { for (j = 0; j < 5; j++) { printf("%d\t", *(arr[i] + j)); } printf("\n"); } return 0; } -
Array parameter passing and pointer parameter passing
- One dimensional array parameters can be passed by array or pointer, and the array size can be omitted
- void test( int arr[ ] ) void test( int* arr )
- Two dimensional array parameters can be transferred by two-dimensional array or array pointer. The rows of the array can be omitted and the columns cannot be omitted
- void test( int arr[ ][ N ] ) void test( int (*arr)[ 5 ])
- The primary pointer is used to transfer parameters
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int a = 10; int* p = &a; test(p); void test(int* p) { }
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- The second level pointer or the first level pointer array is used for parameter transfer
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int n = 10; int* p = &n; int** pp = &p; test(pp); test(&p); int* arr[10]; test(arr); void test(int** ptr) { }
- One dimensional array parameters can be passed by array or pointer, and the array size can be omitted
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Function pointer
- Is a pointer to a function, where the address of the function is stored / / & both the function name and the function name are the address of the function
- Definition: return type (* p) (parameter type) p is the function pointer
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#include <stdio.h> int add(int x,int y) { int z = x + y; return z; } int main() { int (*pa)(int, int) = add; //Both are OK printf("%d\n", (pa)(2, 3)); printf("%d\n", (*pa)(2, 3));//*It doesn't work return 0; } -
//Code 1 //void(*) () 0 converts the mandatory type of 0 to the type of void(*) () function pointer. 0 is a function address //Call the function at address 0 (* (void (*)())0 )(); //Code 2 //signal is a function declaration //The return type of signal is a function pointer void (* signal(int,void(*)(int)) )(int); typedef void(* pfun_t)(int); pfun_t signal(int,pfun_t); typedef unsigned int uint;
C traps and defects
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Function pointer array
- An array of function pointers
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Purpose: transfer table
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#include <stdio.h> 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 menu() { printf("********************\n"); printf("***1.add 2.sub***\n"); printf("***3.mul 4.div***\n"); printf("****** 0.exit ******\n"); } int main() { int input = 0; int x = 0; int y = 0; //pfarr is a function pointer array -- transfer table int (*pfarr[5])(int, int) = {0, add,sub,mul,div }; do { menu(); printf("Please select mode:\n"); scanf_s("%d", &input); if (input >= 1 && input <= 4) { printf("Please enter two operands:\n"); scanf_s("%d%d", &x, &y); int ret = pfarr[input](x, y); printf("The result is:%d\n", ret); } else if (input == 0) { printf("sign out.......\n"); } else { printf("Input error, please reselect:\n"); } } while (input); }
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- An array of function pointers
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Pointer to array of function pointers
- The pointer to the array of function pointers is a pointer, the pointer points to an array, and the array elements are function pointers
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int arr[10] = { 0 }; //Pointer array int (*p)[10] = &arr; //Array of function pointers int(*parr[10])(int, int); //pparr is an array pointer. The array pointed to by the pointer has 10 elements. The element type is function pointer int(*(*pparr)[10])(int, int) = &parr;
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Callback function
- A callback function is a function called through a function pointer. If you pass the pointer (address) of the function as a parameter to another function, when the 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 function, but by another party when a specific event or condition occurs, Used to respond to this event condition
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#include <stdio.h> //Callback function void print(char* str) { printf("hehe:%s\n", str); } void test(void (*p)(char*)) { printf("test\n"); p("bit"); } int main() { test(print); return 0; }Pointer of void * type cannot be dereferenced
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Pointer and array analysis of interview questions