移动或交换字符串流 [英] Move or swap a stringstream

问题描述

我想移动一个字符串流，在现实世界的应用程序中，我有一些字符串流类数据成员，我想在操作过程中将其重用于不同的字符串.

I want to move a stringstream, in the real world application I have some stringstream class data member, which I want to reuse for different string's during operation.

stringstream没有复制分配或复制构造函数，这很有意义.但是，根据cppreference.com和cplusplus.com，std :: stringstream应该定义了移动分配和交换操作.我都尝试过，但都失败了.

stringstream does not have a copy-assignment or copy constructor, which makes sense. However, according to cppreference.com and cplusplus.com std::stringstream should have a move assignment and swap operation defined. I tried both, and both fail.

#include <string>       // std::string
#include <iostream>     // std::cout
#include <sstream>      // std::stringstream

int main () {

  std::stringstream stream("1234");

  //stream = std::move(std::stringstream("5678"));

  stream.operator=(std::move(std::stringstream("5678")));

  //stream.operator=(std::stringstream("5678"));

  return 0;
}

来源: http://ideone.com/Izyanb

prog.cpp:11:56: error: use of deleted function ‘std::basic_stringstream<char>& std::basic_stringstream<char>::operator=(const std::basic_stringstream<char>&)’
   stream.operator=(std::move(std::stringstream("5678")));

编译器指出，这三个语句都没有分配拷贝，这是正确的.但是，我看不到为什么不使用移动分配，特别是因为std :: move应该返回右值引用. Stringstream应该具有移动分配，如下所示: http://en.cppreference.com/w /cpp/io/basic_stringstream/operator％3D

The compiler states that there is no copy assignment for all three statements, which is true. However, I fail to see why it is not using the move-assignment, especially since std::move is supposed to return a rvalue reference. Stringstream should have a move assignment, as shown here: http://en.cppreference.com/w/cpp/io/basic_stringstream/operator%3D

PS:我正在使用c ++ 11，因此右值引用是世界"的一部分.

PS: I'm working with c++11, hence rvalue-references are part of the 'world'.

我发现这很奇怪，我从cplusplus.com复制了示例代码，但失败了:

This I found really strange, I copied example code from cplusplus.com and it failed:

// swapping stringstream objects
#include <string>       // std::string
#include <iostream>     // std::cout
#include <sstream>      // std::stringstream

int main () {

  std::stringstream foo;
  std::stringstream bar;

  foo << 100;
  bar << 200;

  foo.swap(bar);

  int val;

  foo >> val; std::cout << "foo: " << val << '\n';
  bar >> val; std::cout << "bar: " << val << '\n';

  return 0;
}

来源: http://ideone.com/NI0xMS cplusplus.com来源: http://www.cplusplus.com/reference/sstream/stringstream/swap/

source: http://ideone.com/NI0xMS cplusplus.com source: http://www.cplusplus.com/reference/sstream/stringstream/swap/

prog.cpp: In function ‘int main()’:
prog.cpp:14:7: error: ‘std::stringstream’ has no member named ‘swap’
   foo.swap(bar);

我想念什么?为什么不能移动或交换字符串流?我应该如何交换或移动字符串流?

What am I missing? Why can't I move or swap a stringstream? How should I swap or move a stringstream?

推荐答案

这是GCC上缺少的功能:请参见

This is a missing feature on GCC : see bug 54316 , it has been fixed (you can thank Jonathan Wakely) for the next versions (gcc 5)

Clang编译以下代码:

Clang with libc++ compiles this code :

int main () {

  std::stringstream stream("1234");

  std::stringstream stream2 = std::move(std::stringstream("5678"));

  return 0;
}

实时演示

并且 还使用std::stringstream::swap

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