realloc对性能的影响（） [英] Performance impact of realloc ()

问题描述

我有一个记录列表，一开始我不知道记录数。我需要将它们读入数组。
，因此建议一一阅读所有记录。一一重新分配&继续随着元素的出现而增加数组的大小，或者我应该花一遍时间来确定记录数吗？ malloc只做一次吗？哪一个将在计算上更便宜？

I have a list of records, at the starting I dont know the number of records. I need to read them into array. so is it advisable to read all record one by one & doing realloc one by one & go on increasing the array size as the element comes OR should I spend one pass in identifying the number of records & do malloc only once ? Which one will be be less computationally expensive ?

推荐答案

A realloc 不是真的不是很贵。但是为每个元素调用 realloc 有点多。我建议您这样做：

A realloc isn't really very expensive. But calling realloc for each element is a bit much. I suggest you do this:

• 以大小开头


• 添加元素时，请选中如果您有足够的空间


• 当您没有足够的空间时，将当前金额加倍

正确猜测适当的初始大小也有帮助。因此，如果60％的输入少于100条记录，则从此开始。

Correctly guessing an adequate initial size also helps. So if 60% of your inputs are less than 100 records, start with that.

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