std :: string及其自动调整内存大小 [英] std::string and its automatic memory resizing

问题描述

我对C ++很新，但我知道你不能只是使用内存似的std :: string类似乎让你做。例如：

I'm pretty new to C++, but I know you can't just use memory willy nilly like the std::string class seems to let you do. For instance:

std::string f = "asdf";
f += "fdsa";

字符串类如何处理越来越大？我假设它分配一个默认的内存量，如果需要更多，它 new 是一个更大的内存块，并复制本身。但是，这不是很低效，以至于必须复制整个字符串每次它需要调整大小？我不能真正想到另一种方式可以做（但显然有人做了）。

How does the string class handle getting larger and smaller? I assume it allocates a default amount of memory and if it needs more, it news a larger block of memory and copies itself over to that. But wouldn't that be pretty inefficient to have to copy the whole string every time it needed to resize? I can't really think of another way it could be done (but obviously somebody did).

对于这个问题，所有的stdlib类如vector，queue，stack等是如何处理增长和收缩这么透明？

And for that matter, how do all the stdlib classes like vector, queue, stack, etc handle growing and shrinking so transparently?

推荐答案

通常，有一个加倍的算法。换句话说，当它填充当前缓冲区时，它分配一个大两倍的新缓冲区，然后复制当前数据。这导致比通过单个分配块生长的替代方案更少的分配/复制操作。

Usually, there's a doubling algorithm. In other words, when it fills the current buffer, it allocates a new buffer that's twice as big, and then copies the current data over. This results in fewer allocate/copy operations than the alternative of growing by a single allocation block.

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