Re: [C++] std::ostream::rdbuf()

From: Martin Henne (martin.henne_at_web.de)
Date: 10/25/03 

Date: Sat, 25 Oct 2003 20:00:26 +0200

Mike Wahler wrote:

> Show us exactly what you tried, and define 'doesn't work'.

This is the compile error:

 no match for `MyOstream& << <unknown type>' operator

Below is the code (as posted by Stefan before _plus_
the one line in main() that causes this error).

// Code example

 #include <iostream>

class setimportance {
  int imp;
public:
  setimportance(int i):imp(i) {}
  int get_importance() const {return imp;}
};

class MyOstream {
  std::ostream & out;
  int verbosity;
  int importance;
public:
  MyOstream(std::ostream& os)
    : out(os),
    verbosity(0),
    importance(0)
  {
  }
  void set_verbosity(int v) {
    verbosity=v;
  }
  friend MyOstream & operator << (MyOstream & o, setimportance & imp);

  template <typename T>
  MyOstream & operator << (T const & item) {
    if (importance<verbosity)
      out << item;
    return *this;
  }
};

template <>
MyOstream & MyOstream::operator << (setimportance const & imp) {
  importance=imp.get_importance();
  return *this;
}

int main() {
  MyOstream out (std::cout);
  for(int v=1;v<3;++v) {
    out.set_verbosity(v);
    std::cout << "verbosity set to " << v << std::endl;
    out << setimportance(0) << "Hah ... I dont care about verbosity!\n";
    out << setimportance(1) << "Uh ... but I have to!\n";

    out << "This endl causes a compilation error" << std::endl;

  }
}

// End of Code 

-- 
martin dot henne at web dot de

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