使用<<运算符写入文件和cout

Question

我想重载<<运算符来写一个文件和cout所需的值.我试图使用以下代码来完成它,但无法成功.它只是将值写入文本文件.任何帮助,将不胜感激.谢谢.

void operator<<(std::ostream& os, const string& str)
{
    std::cout << str;
    os << str;
}

int main() {
    ofstream fl;
    fl.open("test.txt");
    fl << "!!!Hello World!!!" << endl;
    return 0;
}

Answer 1

创建一个帮助程序类和重载运算符,负责传输到两个流.使用辅助类而不是尝试覆盖重载operator<<函数的标准库实现.

这应该工作:

#include <iostream>
#include <fstream>

struct MyStreamingHelper
{
    MyStreamingHelper(std::ostream& out1,
                      std::ostream& out2) : out1_(out1), out2_(out2) {}
    std::ostream& out1_;
    std::ostream& out2_;
};

template <typename T>
MyStreamingHelper& operator<<(MyStreamingHelper& h, T const& t)
{
   h.out1_ << t;
   h.out2_ << t;
   return h;
}

MyStreamingHelper& operator<<(MyStreamingHelper& h, std::ostream&(*f)(std::ostream&))
{
   h.out1_ << f;
   h.out2_ << f;
   return h;
}

int main()
{
   std::ofstream fl;
   fl.open("test.txt");
   MyStreamingHelper h(fl, std::cout);
   h << "!!!Hello World!!!" << std::endl;
   return 0;
}