有没有一种方法可以从string_view创建一个stringstream而不复制数据？ [英] Is there a way to create a stringstream from a string_view without copying data?

问题描述

我认为这是一个非常简单的问题。我特别想使用 std :: get_time ，但是它需要使用某种流。我在 string_view 中传递数据，并希望避免为了分析日期而复制它。

I think that's a pretty straighforward question. I'd specifically like to use std::get_time, but it requires some sort of a stream to be used with. I am passing the data in a string_view and would like to avoid copying it just to parse the date.

推荐答案

您可以使用Boost.Iostreams库轻松做到这一点：

You can do that easily with Boost.Iostreams library:

#include <boost/iostreams/device/array.hpp>
#include <boost/iostreams/stream.hpp>

#include <iostream>
#include <string>

int main() {
    std::string_view buf{"hello\n"};
    boost::iostreams::stream<boost::iostreams::basic_array_source<char>> stream(buf.begin(), buf.size());

    std::string s;
    stream >> s;
    std::cout << s << '\n';
}

---

您应该能够使用 std :: stringstream 和 std :: basic_stringbuf< CharT，Traits，Allocator> :: setbuf ，但C ++标准降低了其要求：

---

You should be able to do that with std::stringstream and std::basic_stringbuf<CharT,Traits,Allocator>::setbuf but the C++ standard botched its requirements:

[ setbuf ]的效果是实现定义的：某些实现不执行任何操作，而某些实现则清除 std :: string 成员当前用作缓冲区，并开始使用用户提供的大小为 n 的字符数组，其第一个元素为 s 指向的缓冲区和输入/输出字符序列。

The effect [of setbuf] is implementation-defined: some implementations do nothing, while some implementations clear the std::string member currently used as the buffer and begin using the user-supplied character array of size n, whose first element is pointed to by s, as the buffer and the input/output character sequence.

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