C language learning diary 3 - realloc function

Catalog

One 、 Small expansion

1.1 Code

1.2 result

Two 、 Large capacity expansion

2.1 Code

2.2 result

2.3 Explain

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One 、 Small expansion

1.1 Code

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int* arr1 = (int*)malloc(10 * 4);
    for (int i = 0; i < 10; i++) {
        arr1[i] = i;
    }
    for (int i = 0; i < 10; i++) {
        printf("%d ", arr1[i]);
    }
    printf("\n");

    int* arr2 = (int*)realloc(arr1, 20 * 4);
    for (int i = 0; i < 20; i++) {
        printf("%d ", arr2[i]);
    }
    printf("\n");

    printf("%p %p\n", arr1, arr2);

    return 0;
}

1.2 result

0 1 2 3 4 5 6 7 8 9 
0 1 2 3 4 5 6 7 8 9 2080374908 47324 -457679488 407 -457703088 407 1174430068 1113543504 1398230866 1096766021
00000197e4b813d0 00000197e4b813d0

Two 、 Large capacity expansion

2.1 Code

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int* arr1 = (int*)malloc(10 * 4);
    for (int i = 0; i < 10; i++) {
        arr1[i] = i;
    }
    printf("\n");

    int* arr2 = (int*)realloc(arr1, 100000 * 4);

    printf("%p %p\n", arr1, arr2);

    return 0;
}

2.2 result

0000023f788313d0 0000023f78a10080

2.3 Explain

Small expansion increases memory on the original basis

Large expansion is to delete the original memory and reallocate a piece of memory , The suggestion is not to use the original pointer to operate the memory

We can use the following form  

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int* arr1 = (int*)malloc(10 * 4);
    for (int i = 0; i < 10; i++) {
        arr1[i] = i;
    }
    printf("\n");

    arr1 = (int*)realloc(arr1, 100000 * 4);

    printf("%p\n", arr1);

    return 0;
}