详解C语言中动态内存管理及柔性数组的使用

int main()
{
    int* p = (int*)malloc(40);
    if (p == NULL)
    {
        printf("%s\n", strerror(errno));
        return 1;
    }
    free(p);
    p = NULL;
    return 0;
}

int main()
{
    int* p = (int*)realloc(NULL, 40);
    return 0;
}

void text()
{
    int* p = (int*)realloc(NULL, 40);
    if (p == NULL)//判断p是否为空指针
    {
        return;
    }
    *p = 20;
}

void text()
{
    int* p = (int*)realloc(NULL, 40);
    int* m = p;
    if (p == NULL)
    {
        return;
    }
    for (int i = 0; i <= 10; i++)
    {
        p[i] = i;//越界
        p++;
    }
}

void text()
{
    int arr[] = {1,2,3};
    int* p = arr;
    free(p);//不能对非动态开辟的空间进行free
}

void text()
{
    int* p = (int*)malloc(40);
    p++;
    free(p);//p不再指向动态开辟空间的起始位置
}

void text()
{
    int* p = (int*)realloc(NULL, 40);
    free(p);
    //p = NULL;
 
    free(p);
}

void text()
{
    int* p = (int*)realloc(NULL, 40);
    int a = 0;
    scanf("%d", &a);
    if (a == 5)
        return;
    free(p);
    p = NULL;
}

struct S
{
    int a;
    int arr[0];//这里的arr[0]代表未知大小的数组
};
//或者如下写法：
struct S
{
    int a;
    int arr[];
};

struct S
{
    int a;
    int arr[0];
};
int main()
{
    struct S s;
    struct S* ps = &s;
    ps = (struct S*)realloc(NULL,sizeof(s) + 40);//首次开辟空间，传NULL
    if (ps == NULL)
    {
        exit(-1);
    }
    free(ps);
    ps = NULL;
    return 0;
}

struct S
{
    int a;
    int* parr;
};
int main()
{
    struct S* p = (struct S*)malloc(sizeof(struct S));//对结构体动态开辟空间
    if (p == NULL)
    {
        exit(-1);
    }
    int* tmp= (int*)malloc(sizeof(int) * 2);//在堆区动态开辟一块空间
    if (tmp == NULL)
    {
        exit(-1);
    }
    p->parr = tmp;
    free(p->parr);//释放时，需要先释放p->parr指向的空间
    p->parr = NULL;
    free(p);//再将结构体指针p指向的空间释放
    p = NULL;
    return 0;
}