c++ - 重定向后重置 cout

Question

我有一个 C++ 程序，在我使用的程序中:

static ofstream s_outF(file.c_str());
if (!s_outF)
{
    cerr << "ERROR : could not open file " << file << endl;
    exit(EXIT_FAILURE);
}
cout.rdbuf(s_outF.rdbuf());

意思是我将我的 cout 重定向到一个文件。将 cout 返回到标准输出的最简单方法是什么？

谢谢。

Answer 1

在更改 cout 的 streambuf 之前保存旧的 streambuf:

auto oldbuf = cout.rdbuf();  //save old streambuf

cout.rdbuf(s_outF.rdbuf());  //modify streambuf

cout << "Hello File";        //goes to the file!

cout.rdbuf(oldbuf);          //restore old streambuf

cout << "Hello Stdout";      //goes to the stdout!

---

你可以写一个 restorer 来自动完成:

class restorer
{
   std::ostream   & dst;
   std::ostream   & src;
   std::streambuf * oldbuf;

   //disable copy
   restorer(restorer const&);
   restorer& operator=(restorer const&);
  public:   
   restorer(std::ostream &dst,std::ostream &src): dst(dst),src(src)
   { 
      oldbuf = dst.rdbuf();    //save
      dst.rdbuf(src.rdbuf());  //modify
   }
  ~restorer()
   {
      dst.rdbuf(oldbuf);       //restore
   }
};

现在基于作用域使用它:

cout << "Hello Stdout";      //goes to the stdout!

if ( condition )
{
   restorer modify(cout, s_out);

   cout << "Hello File";     //goes to the file!
}

cout << "Hello Stdout";      //goes to the stdout!

最后一个 cout 将输出到 stdout 即使 condition 为 true 且 if block 被执行。