是否移动分配 std::fstream 关闭原始流
Does move assign an std::fstream close the original stream
从 c++11 开始，我们可以将一个 std::fstream 对象分配给另一个对象，但我找不到说明如果 fstream 对象已经与一个文件 (is_open()==true).
所以我的问题是在下面的代码中，File1.txt 是否会正确关闭，或者我是否必须手动关闭它。如果我必须手动完成，如果我不这样做会怎样？
std::fstream file("File1.txt");
file = std::fstream("File2.txt"); //will this implicitly call file.close()?
由于实际的文件相关机制 'hidden' 在相应的缓冲区内（流实际上主要提供格式化 IO），您应该查看 std::basic_filebuf 文档：
First calls close() to close the associated file, then moves the
contents of rhs into *this: the put and get buffers, the associated
file, the locale, the openmode, the is_open flag, and any other state.
After the move, rhs is not associated with a file and rhs.is_open() ==
false.
复制自http://en.cppreference.com/w/cpp/io/basic_filebuf/operator%3D
fstream 对象的移动分配将导致其关联的 filebuf 的移动分配。该文档非常清楚地表明旧文件首先关闭（好像 file.rdbuf()->close() 而不是 file.close()）：
basic_filebuf& operator=(basic_filebuf&& rhs);
- Effects: Calls
this->close() then move assigns from rhs. After the move assignment *this has the observable state it would have had if it had been move constructed from rhs.
- Returns:
*this.
basic_fstream& operator=(basic_fstream&& rhs);
- Effects: Move assigns the base and members of
*this from the base and corresponding members of rhs.
- Returns:
*this.
（这是草案 n4527 中的措辞，至少自 n3485 以来未更改）
从 c++11 开始，我们可以将一个 std::fstream 对象分配给另一个对象，但我找不到说明如果 fstream 对象已经与一个文件 (is_open()==true).
所以我的问题是在下面的代码中，File1.txt 是否会正确关闭，或者我是否必须手动关闭它。如果我必须手动完成，如果我不这样做会怎样？
std::fstream file("File1.txt");
file = std::fstream("File2.txt"); //will this implicitly call file.close()?
由于实际的文件相关机制 'hidden' 在相应的缓冲区内（流实际上主要提供格式化 IO），您应该查看 std::basic_filebuf 文档：
First calls close() to close the associated file, then moves the contents of rhs into *this: the put and get buffers, the associated file, the locale, the openmode, the is_open flag, and any other state. After the move, rhs is not associated with a file and rhs.is_open() == false.
复制自http://en.cppreference.com/w/cpp/io/basic_filebuf/operator%3D
fstream 对象的移动分配将导致其关联的 filebuf 的移动分配。该文档非常清楚地表明旧文件首先关闭（好像 file.rdbuf()->close() 而不是 file.close()）：
basic_filebuf& operator=(basic_filebuf&& rhs);
- Effects: Calls
this->close()then move assigns fromrhs. After the move assignment*thishas the observable state it would have had if it had been move constructed fromrhs.- Returns:
*this.
basic_fstream& operator=(basic_fstream&& rhs);
- Effects: Move assigns the base and members of
*thisfrom the base and corresponding members ofrhs.- Returns:
*this.
（这是草案 n4527 中的措辞，至少自 n3485 以来未更改）