（C）将数组与动态内存分配一起使用

您不应该将每realloc()一个可能变得非常大，非常快的内存加倍。通常，您仅以小块形式扩展内存。realloc()如果旧的内存不能足够长的话，它也有讨厌的习惯来使用内存的另一部分。如果失败，则将旧存储器中的所有数据丢失。通过使用临时指针指向新内存并在成功分配之后交换它们，可以避免这种情况。这只需要额外的指针（最多4个或8个字节）和一个交换（最多只需要几个CPU周期）就可以了。要小心x86，xchg它在多个处理器的情况下会使用锁，这是非常昂贵的！）

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

// would normally be some small power of two, like
// e.g.: 64 or 256
#define REALLOC_GROW 10
int main()
{
  // a needs to be NULL to avoid a first malloc()
  int *a = NULL, *cp;
  // to avoid complications allocated is int instead of size_t
  int allocated = 0, length = 0, i, ch, r;

  printf("Fill up your array: ");
  while (1) {
    // Will also do the first allocation when allocated == length
    if (allocated <= length) {
      // realloc() might choose another chunk of memory, so
      // it is safer to work on copy here, such that nothing is lost
      cp = realloc(a, (allocated + REALLOC_GROW) * sizeof(int));
      if (cp == NULL) {
        fprintf(stderr, "Malloc failed\n");
        // but we can still use the old data
        for (i = 0; i < length; i++) {
          printf("%d ", a[i]);
        }
        // that we still have the old data means that we need to
        // free that memory, too
        free(a);
        exit(EXIT_FAILURE);
      }
      a = cp;
      // don't forget to keep the amount of memory we've just allocated
      allocated += REALLOC_GROW;
    }
    // out, if user typed in anything but an integer
    if ((r = scanf("%d", &ch)) != 1) {
      break;
    }
    a[length] = ch;
    length++;
  }

  printf("Your array is: \n");
  // keep informations together, set i=0 in the loop
  for (i = 0; i < length; i++) {
    printf("%d ", a[i]);
  }
  fputc('\n', stdout);
  // clean up
  free(a);

  exit(EXIT_SUCCESS);
}

如果你玩了一下周围用的启动值allocated，价值REALLOC_GROW和使用乘法，而不是加法的realloc()和更换if(allocated <= length)用if(1)，你可以触发没有内存不足的错误，看看它是否仍然打印你之前输入的内容。现在，通过a直接使用更改复制时的重新分配，并查看它是否打印数据。情况仍然可能如此，但现在不再保证。