用C的realloc双二维数组 [英] Realloc double 2D array in C

问题描述

我写这应该realloc的每个输入数组的功能。我认为，功能效果很好，但是当我试图用我得到段错误的阵列的工作。

I wrote an function which should realloc the array for each input. I think that function works well, but when I'm trying to work with the array I got segmentation fault.

输入：

[1,2] [6,3] [2.5,3.5]

我要检查，如果用户以正确形式'['号'，'数']'进入输入。我必须至少有2项。输入的到底是不是新的生产线，但EOF（<大骨节病> CTRL + <大骨节病> D 或<大骨节病> CTRL + <大骨节病>以Z ）。

I have to check if the user enters input in the correct form '[' number ',' number ']'. I have to have at least 2 entries. The end of input isn't new line, but EOF (CTRL+D or CTRL+Z).

我的code：

double ** allocation (double ** field, int i)
{
   double x = 0, y = 0;
   char obr[1], cbr[1], col[1];

   while (scanf("%c%lf%c%lf%c", &obr, &x, &col, &y, &cbr) == 5)
   {
       if (col[0] != ',' || obr[0] != '[' || cbr[0] != ']')
           return 0;

       field = (double **) realloc(field, (i + 1) * sizeof(*field));
       if (field == NULL)
           return 0;

       field[i] = (double *)malloc(2 * sizeof(double));
       if (field[i] == 0)
           return 0;

       field[i][0] = x;
       field[i][1] = y;
       i++;
  }
  if (feof (stdin))
      return 0;

  return field;
}

而当我想用这样的：

And when I want to use this:

double min = sqrtf(powf(field[0][0] - field[1][0], 2) + powf(field[0][1] - field[1][1], 2));

我会得到我的分段错误。

I will get my segmentation fault.

推荐答案

从男人的realloc （重点煤矿）：

该realloc（）的函数试图改变分配的大小指出
  通过PTR大小，并返回PTR。如果没有足够的空间来
  加大内存分配由ptr指向，的realloc（）创建一个新的
  分配，复制尽可能多的旧数据由ptr为适合
  新的分配，释放旧的分配，并返回一个指针
  分配的内存。

The realloc() function tries to change the size of the allocation pointed to by ptr to size, and returns ptr. If there is not enough room to enlarge the memory allocation pointed to by ptr, realloc() creates a new allocation, copies as much of the old data pointed to by ptr as will fit to the new allocation, frees the old allocation, and returns a pointer to the allocated memory.

你不能保证，当你使用使用相同的内存的realloc ，你需要通过指针回的情况下，它的被移动到新位置。您可以通过检查它是否是一个空指针或没有，太检查成功。

You're not guaranteed to be using the same memory when you use realloc, you need to pass the pointer back for the case that it's been moved to a new location. You can check for success by checking whether it's a NULL pointer or not, too.

TL;博士：您需要使用返回字段而不是收益1 或返回0 。

tl;dr: You need to use return field instead of return 1 or return 0.

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