std::basic_ios<CharT,Traits>::copyfmt (3) - Linux Manuals

std::basic_ios<CharT,Traits>::copyfmt: std::basic_ios<CharT,Traits>::copyfmt


std::basic_ios<CharT,Traits>::copyfmt - std::basic_ios<CharT,Traits>::copyfmt


basic_ios& copyfmt(const basic_ios& other);

If other refers to the same object as *this, has no effects. Otherwise, copies the state of the stream other into *this. This is done in the following sequence:
1) Calls every callback registered by register_callback() passing erase_event as parameter
2) Copies all member objects from other to *this except for rdstate(), the exception mask, and rdbuf(). In particular, makes copies of the locale, the formatting flags, the contents of the arrays std::ios_base::iword and std::ios_base::pword (but not the iword and pword pointers themselves), the callbacks, and the tied stream.
3) Calls every callback registered by register_callback() passing copyfmt_event as parameter
4) Copies the exception mask from other to *this as if by calling exceptions(other.exceptions())


other - another stream to use as source

Return value



The second pass through the callbacks may be used to deep-copy the user-defined objects pointed to by the pointers in std::ios_base::pword
copyfmt() may be used to save and restore the state of a stream. Boost provides a more fine-grained IO_state_savers library for the same purpose.


makes the ofstream object "out" behave exactly like std::cout, including formatting, tie() to std::cin, etc.
// Run this code

  #include <iostream>
  #include <fstream>

  int main()
      std::ofstream out;

      out.copyfmt(std::cout); // copy everything except rdstate and rdbuf
      out.clear(std::cout.rdstate()); // copy rdstate
      out.basic_ios<char>::rdbuf(std::cout.rdbuf()); // share the buffer

      out << "Hello, world\n";


  Hello, world