C语言详细讲解多维数组与多维指针

#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("%p\n", p);
    if(reset(&p, 5, 3))
    {
        printf("%p\n", p);
    }
    
   free(p);
   
   return 0;
}

#include <stdio.h>
#include <malloc.h>
 
void printArray(int a[], int size)
{
    int i = 0;
    
    printf("printArray: %d\n", sizeof(a));
 
    for(i = 0; i < size; i++)
    {
        printf("%d\n", a[i]);
    }
}
 
int main()
{
    int a[3][3] = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
    int* p = &a[0][0];
    
    int i = 0;
    int j = 0;
    
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            printf("%d, ", *(*(a+i) + j));
        }
        
        printf("\n");
    }
    
    printf("\n");
    
    printArray(p, 9);
    
    return 0;
}

#include <stdio.h>
 
int main(void)
{
    int a[3][3] = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };
    printf("%p %p %p %p\n", &a[0][0], a, a[0], *a);
    printf("%p %p %p %p %p\n", &a[0][0] + 1, a + 1, a[1], *(a + 1), &a[1][0]);
    printf("%p %p %p %p\n", (a + 1) + 1, a + 1 + 1, &a[1][1], &a[2][0]);
    printf("%d %d\n", *(*(a + 1) + 1), a[1][1]);
    return 0;
}
 

#include <stdio.h>
#include <malloc.h>
 
int** malloc2d(int row, int col)
{
    int** ret = NULL;
    
    if( (row > 0) && (col > 0) )
    {
        int* p = NULL;
        
        ret = (int**)malloc(row * sizeof(int*));
        p = (int*)malloc(row * col * sizeof(int));
        
        if( (ret != NULL) && (p != NULL) )
        {
            int i = 0;
            
            for(i = 0; i < row; i++)
            {
                ret[i] = p + i * col;
            }
        }
        else
        {
            free(ret);
            free(p);
            
            ret = NULL;
        }
        
    }
    
    return ret;
}
 
void free2d(int** p)
{
    if( *p != NULL )
    {
        free(*p);
    }
    
    free(p);
}
 
int main()
{
    int** a = malloc2d(3, 3);
    int i = 0;
    int j = 0;
    
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            printf("%d, ", a[i][j]);
        }
        
        printf("\n");
    }
    
    free2d(a);
    
    return 0;
}