[英]What does ifstream::rdbuf() actually do?
I have the following code and it works pretty good (other than the fact that it's pretty slow, but I don't care much about that).我有以下代码,它工作得很好(除了它很慢,但我不太关心这一点)。 It doesn't seem intuitive that this would write the entire contents of the infile to the outfile.
将 infile 的全部内容写入 outfile 似乎并不直观。
// Returns 1 if failed and 0 if successful
int WriteFileContentsToNewFile(string inFilename, string outFilename)
{
ifstream infile(inFilename.c_str(), ios::binary);
ofstream outfile(outFilename.c_str(), ios::binary);
if( infile.is_open() && outfile.is_open() && infile.good() && outfile.good() )
{
outfile << infile.rdbuf();
outfile.close();
infile.close();
}
else
return 1;
return 0;
}
Any insight?任何见解?
iostream
classes are just wrappers around I/O buffers. iostream
类只是 I/O 缓冲区的包装器。 The iostream
itself doesn't do a whole lot… mainly, it the provides operator>>
formatting operators. iostream
本身并没有做很多事情……主要是,它提供了operator>>
格式化操作符。 The buffer is provided by an object derived from basic_streambuf
, which you can get and set using rdbuf()
.缓冲区由从
basic_streambuf
派生的对象提供,您可以使用rdbuf()
获取和设置该对象。
basic_streambuf
is an abstract base with a number of virtual functions which are overridden to provide a uniform interface for reading/writing files, strings, etc. The function basic_ostream<…>::operator<<( basic_streambuf<…> )
is defined to keep reading through the buffer until the underlying data source is exhausted. basic_streambuf
是一个抽象基础,具有许多虚函数,这些虚函数被覆盖以提供用于读/写文件、字符串等的统一接口。函数basic_ostream<…>::operator<<( basic_streambuf<…> )
被定义为保持读取缓冲区,直到底层数据源耗尽。
iostream
is a terrible mess, though. iostream
是一团糟。
Yes, it's specified in the standard and it's actually quite simple.是的,它在标准中有规定,实际上很简单。
rdbuf()
just returns a pointer to the underlying basic_streambuf
object for the given [io]stream
object. rdbuf()
只是返回一个指向给定[io]stream
对象的基础basic_streambuf
对象的指针。
basic_ostream<...>
has an overload for operator<<
for a pointer to basic_streambuf<...>
which writes out the contents of the basic_streambuf<...>
. basic_ostream<...>
具有用于过载operator<<
指针是指向basic_streambuf<...>
其中写出的内容basic_streambuf<...>
快速查看源代码表明basic_ofstream
是basic_filebuf
的包装器。
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