如何获得的结构在C中动态创建数组的长度？ [英] How to get the length of a dynamically created array of structs in C?

问题描述

目前我正在试图获得一个动态生成的数组的长度。它是结构的数组：

I am currently trying to get the length of a dynamically generated array. It is an array of structs:

typedef struct _my_data_ 
{
  unsigned int id;
  double latitude;
  double longitude;
  unsigned int content_len;
  char* name_dyn;
  char* descr_dyn;
} mydata;

我intialize我的数组这样的：

I intialize my array like that:

mydata* arr = (mydata*) malloc(sizeof(mydata));

和再调整它使用的的realloc 并开始与数据来填充它。

And then resized it using realloc and started to fill it with data.

我然后试图用code描述<一个得到它的大小href=\"http://stackoverflow.com/questions/37538/how-do-i-determine-the-size-of-my-array-in-c\">here.

I then attempted to get its size using the code described here.

sizeof(arr) / sizeof(arr[0])

此操作返回 0 ，即使我的数组包含两个元素。

This operation returns 0 even though my array contains two elements.

可能有人请告诉我，我在做什么错了？

Could someone please tell me what I'm doing wrong?

推荐答案

如果你需要知道一个动态分配的数组的大小，你要跟踪它自己。

If you need to know the size of a dynamically-allocated array, you have to keep track of it yourself.

的的sizeof（ARR）/ sizeof的（ARR [0]）技术只适用于数组的大小在编译时是已知的，对C99的的variable-length阵列的。

The sizeof(arr) / sizeof(arr[0]) technique only works for arrays whose size is known at compile time, and for C99's variable-length arrays.

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