C++ ifstream::rdbuf() 实际上是做什么的？
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What does ifstream::rdbuf() actually do?
提问by Brian T Hannan
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). It doesn't seem intuitive that this would write the entire contents of the infile to the outfile.
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）。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？
采纳答案by CB Bailey
Yes, it's specified in the standard and it's actually quite simple. rdbuf()just returns a pointer to the underlying basic_streambufobject for the given [io]streamobject.
是的，它在标准中有规定，实际上很简单。rdbuf()只返回一个指向给basic_streambuf定[io]stream对象的底层对象的指针。
basic_ostream<...>has an overload for operator<<for a pointer to basic_streambuf<...>which writes out the contents of the basic_streambuf<...>.
basic_ostream<...>有一个operator<<指针的重载，用于basic_streambuf<...>写出basic_streambuf<...>.
回答by Potatoswatter
iostreamclasses are just wrappers around I/O buffers. The iostreamitself doesn't do a whole lot… mainly, it the provides operator>>formatting operators. The buffer is provided by an object derived from basic_streambuf, which you can get and set using rdbuf().
iostream类只是 I/O 缓冲区的包装器。它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。缓冲区由派生自 的对象提供basic_streambuf，您可以使用 获取和设置该对象rdbuf()。
basic_streambufis 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。该函数basic_ostream<…>::operator<<( basic_streambuf<…> )被定义为继续读取缓冲区，直到底层数据源耗尽。
iostreamis a terrible mess, though.
iostream然而，这是一个可怕的混乱。
