Question

我很想将此代码用作动态数组。不幸的是，我无法弄清楚为什么程序不使用分配的内存。可能是AddToArray函数的参数有问题吗？

可以将此代码直接复制并粘贴到IDE中并进行编译，以查看输出。内存似乎已分配但未使用？

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

typedef struct {
    float x;
    float y;
} DATA;

int AddToArray (DATA item, 
                DATA **the_array,
                int *num_elements,
                int *num_allocated)
{
  if(*num_elements == *num_allocated) 
  { // Are more refs required?

    // Feel free to change the initial number of refs
    // and the rate at which refs are allocated.
    if (*num_allocated == 0)
    {
      *num_allocated = 3; // Start off with 3 refs
    }
    else
    {
      *num_allocated *= 2;
    }// Double the number of refs allocated

    // Make the reallocation transactional by using a temporary variable first
    void *_tmp = realloc(*the_array, (*num_allocated * sizeof(DATA)));

    // If the reallocation didn't go so well, inform the user and bail out
    if (!_tmp)
    { 
      printf("ERROR: Couldn't realloc memory!\n");
      return(-1); 
    }
    // Things are looking good so far, so let's set the 
    *the_array = (DATA*)_tmp;   
  }

  (*the_array)[*num_elements] = item; 
  *num_elements++;

  return *num_elements;
}

int main()
{  
  DATA *the_array = NULL;
  int num_elements = 0; // To keep track of the number of elements used
  int num_allocated = 0; // This is essentially how large the array is

  // Some data that we can play with
  float numbers1[4] = {124.3,23423.4, 23.4, 5.3};
  float numbers2[4] = { 42, 33, 15, 74 };
  int i;    
  // Populate!
  for (i = 0; i < 4; i++)
  {
    DATA temp;
    temp.x = numbers1[i];
    temp.y = numbers2[i];
    if (AddToArray(temp, &the_array, &num_elements, &num_allocated) == -1)
    return 1;               // we'll want to bail out of the program.
  }

  for (i = 0; i < 4; i++)
  {
    printf("(x:%f,y:%f)\n", the_array[i].x, the_array[i].y);
  }
  printf("\n%d allocated, %d used\n", num_allocated, num_elements);
  // Deallocate!
  free(the_array);  
  // All done.
  return 0;
}

Answer 1

在您的代码中，您需要更改

*num_elements++;

到

(*num_elements)++;

因为没有明确的括号，++优先于*运算符。你想要的是增加存储在地址中的值，而不是相反。

检查运营商优先级here。

Answer 2

试

(*num_elements)++;

在功能

AddToArray()

Answer 3

代码中的错误是指针递增，而不是值。

..
    (*the_array)[*num_elements] = item; 
    (*num_elements)++;
..

这是某种编程任务吗？这里的代码可以在很多方面得到改进。这类问题有很多很好的算法，写得很好，优化得很好，我建议你在那个领域进行一些研究。

动态数组已分配，但无法使用它

3 个答案: