如何在函数内部为数组分配内存 [英] How can I allocate memory for array inside a function

问题描述

我正在尝试从用户那里收到一个电话号码. 并在函数内创建一个具有该数字的数组. 这是我的一些尝试，我遇到了运行时错误. 非常感谢您的帮助.

I am trying to receive a number from the user. And create an array with that number, but, inside a function. Here are my few attempts, I get into run time errors. Help is very much appreciated.

#include <stdio.h>
#include <stdlib.h>
int* Init(int* p, int num);
int main() {
    int *p;
    int num, i;
    puts("Enter num of grades:");
    scanf("%d", &num);

    Init(&p, num);
    //for (i = 0; i < num; i++)
    //{
    //  scanf("%d", &p[i]);
    //}
    free(p);
}
int* Init(int* p, int num)
{
    int *pp;
    p = (int *)malloc(num*sizeof(int));
    if (!pp)
    {
        printf("Cannot allocate memory\n");
        return;
    }
    p = pp;
    free(pp);
}

推荐答案

到目前为止，您已经做得很好，您需要将指针传递给指针.但是您的函数签名不带int **.您要么传递一个指向该指针的指针，然后将分配的内存存储在其中:

You have done well upto the point you understood you need to pass a pointer to pointer. But your function signature doesn't take an int **. Either you pass a pointer to pointer and store the allocated memory in it:

void Init(int **pp, int num)
{
    int *p;
    p = malloc(num*sizeof(int));
    if (!p)
    {
        printf("Cannot allocate memory\n");
    }
    *pp = p;
}

并检查Init()是否返回正确的指针:

And check if the Init() returns a proper pointer:

   Init(&p, num);
   if(p == NULL) {
      /*Memory allocation failed */
   }

---

或分配内存并返回指针:

---

Or allocate memory and return the pointer:

int* Init(int num)
{
    int *p;
    p = malloc(num*sizeof(int));
    if (!p)
    {
        printf("Cannot allocate memory\n");
    }

    return p;
}

并从main()调用为:

int * p = Init(num);
if(p == NULL) {
   /*Memory allocation failed */
}

---

相应地更改Init()的原型.

---

Change the prototype of Init() accordingly.

在任何情况下，都不能在Init()中使用free()指针.这只会立即取消分配内存，您将剩下一个 悬挂指针 .

In any case, you must not free() the pointer in Init(). That just de-allocates memory immediately and you'll be left with a dangling pointer.

完成后，您需要在main()中的free().

And you need to free() in the main() after you are done with it.

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