1. Pointer variables occupy a certain amount of space in memory
2. You can define a pointer to save the address value of the pointer variable
3. Pointers are also variables in essence, and there are also call-by-value and call-by-reference for pointers
#include <stdio.h>#include <malloc.h>int reset(char**p, int size, int new_size){ int ret = 1; int i = 0; int len = 0; char* pt = NULL; char* tmp = NULL; char* pp = *p; if( (p != NULL) && (new_size > 0) ) { pt = (char*)malloc(new_size); tmp = pt; len = (size < new_size) ? size : new_size; for(i=0; i<len; i++) { *tmp++ = *pp++; } free(*p); *p = pt; } else { ret = 0; } return ret;}int main(){ char* p = (char*)malloc(5); printf("%0X\n", p); if( reset(&p, 5, 3) ) { printf("%0X\n", p); } return 0;}
Two-dimensional array and two-level pointer
1. Two-dimensional arrays are arranged in a one-dimensional manner in memory
2. The first dimension in a two-dimensional array is a one-dimensional array
3. The second dimension in the two-dimensional array is the specific value
4. The array name of a two-dimensional array can be regarded as a constant pointer
5. The name of the two-dimensional array represents an array pointer. The two-dimensional array can be regarded as a one-dimensional array. Each element in the two-dimensional array is a one-dimensional array of the same type.
#include <stdio.h>int main(){ int a[5][5]; int(*p)[4];//Array pointer p = a; printf("%d\n", &p[4 ][2] - &a[4][2]);//Offset 18 minus offset 22}
Summarize:
1. There is only one-dimensional array in C language, and the size of the array must be determined as a constant at compile time
2. Array elements in C language can be any type of data, that is, the elements of an array can be another array
3. In C language, only the size of the array and the address of the first element of the array are directly determined by the compiler