是std :: stringstream比std :: string更好的累积吗？ [英] Is std::stringstream better to accumulate than std::string?

问题描述

我知道 std :: stringstream 的优点之一是它是一个 std :: istream 因此它可以接受来自定义运算符<到 std :: istream 的任何类型的输入，原始类型。

I know one of the advantages of the std::stringstream is that it is a std::istream so it may accept input from any type that defines operator<< to std::istream, and also to the primitives type.

我不打算使用运算符<< ，我只是要连接很多字符串。 std :: stringstream 的实现是否使得它比 std :: string 更快，以连接很多字符串？ / p>

I am not going to use the operator<<, I am just going to concatenate a lot of strings. Does the implementation of std::stringstream make it faster than std::string to concatenate a lot of strings?

推荐答案

没有理由期望 std :: string 比 stringstream 的插入函数慢。 std :: string 通常只是一个可能的内存分配/复制，加上将数据复制到内存中。 stringstream 必须处理诸如locales等等，甚至是基本的写调用。

There's no reason to expect std::string's appending functions to be slower than stringstream's insertion functions. std::string will generally be nothing more than a possible memory allocation/copy plus copying of the data into the memory. stringstream has to deal with things like locales, etc, even for basic write calls.

此外， std :: string 提供了最小化或消除第一次内存分配的方法。如果你保留足够的空间，每个插入只是一个 memcpy 。这不是真正可能的 stringstream 。

Also, std::string provides ways to minimize or eliminate anything but the first memory allocation. If you reserve sufficient space, every insertion is little more than a memcpy. That's not really possible with stringstream.

即使它比 std :: string 的附加函数，您仍然可以从 stringstream 中复制字符串来执行操作。这是另一个分配+副本，你不需要 std :: string 。

Even if it was faster than std::string's appending functions, you still have to copy the string out of the stringstream to do something with it. So that's another allocation + copy, which you won't need with std::string.

std :: stringstream 如果您需要格式，而不仅仅是将一些字符串粘在一起。

You should use std::stringstream if you need formatting, not just for sticking some strings together.

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