为什么我不能移动std :: ofstream？ [英] Why can't I move std::ofstream?

问题描述

看看之前的答案，看起来虽然 std :: ostream 不是可移动的， std :: ofstream 应该是。但是，此代码

Looking at previous answers on SO, it seems that while std::ostream is not be movable, std::ofstream should be. However, this code

#include <fstream>

int main()
{
    std::ofstream ofs;
    std::ofstream ofs2{std::move(ofs)};
}

似乎没有在任何版本的gcc或clang中编译我试过--std = c ++ 11或--std = c ++ 14）。编译器错误有点不同，但这是我得到的gcc 4.9.0

does not seem to compile in any version of gcc or clang I tried (with either --std=c++11 or --std=c++14). The compiler error varies somewhat, but here's what I get for gcc 4.9.0

6 : error: use of deleted function 'std::basic_ofstream::basic_ofstream(const std::basic_ofstream&)'

根据标准？

请注意，之前问过一个非常类似的问题（是std :: ofstream可移动吗？），但似乎标准已经改变了自那以后（详细在
为什么不能std :: ostream被移动？）渲染这些答案过时。当然，没有这些答案解释为什么上面的代码不编译。

Note that a very similar question was asked before ( Is std::ofstream movable? ) but seems the standard has changed since then ( as detailed in Why can't std::ostream be moved? ) rendering those answers outdated. Certainly, none of those answers explains why the code above does not compile.

当尝试使用 ofstream 的容器时遇到此问题，由于上述原因，它不工作。 / p>

Came across this issue when trying to use containers of ofstream, which does not work because of the above.

推荐答案

根据标准

27.9.1.11 basic_ofstream构造函数

27.9.1.11 basic_ofstream constructors

或者，它更可读的版本 http://en.cppreference.com/w/cpp/io/basic_ofstream/basic_ofstream ， std :: basic_ostream<> 有一个移动构造函数，因此代码应该编译。

or, its more "readable" version http://en.cppreference.com/w/cpp/io/basic_ofstream/basic_ofstream , std::basic_ostream<> has a move constructor, so the code should compile.

clang ++ 3.5使用 -std = c ++ 11 或 -std = c ++ 1y 。也gcc5编译它，所以可能它没有实现在libstdc ++ gcc< 5

clang++ 3.5 compiles it with -std=c++11 or -std=c++1y. Also gcc5 compiles it, so probably it is not implemented in libstdc++ for gcc < 5

有趣的是，缺少move语义在gcc的stdlibc ++实现中没有提及 https://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2014

Interestingly, the lack of move semantics is not mentioned on gcc's stdlibc++ implementation https://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2014

请参阅 https：//gcc.gnu .org / bugzilla / show_bug.cgi？id = 54316 的错误报告，感谢@BoBTFish指出。已确认问题已在gcc5中修复。

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54316 for a bug report, thanks to @BoBTFish for pointing out. It is confirmed that the issue was fixed in gcc5.

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