std::basic_ios::copyfmt

 

C++

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Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

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basic_streambuf

basic_filebuf

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istrstream (deprecated in C++98)

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basic_osyncstream (C++20)

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streamoff

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iostream_category (C++11)

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std::basic_ios

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basic_ios::basic_ios

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basic_ios::copyfmt

basic_ios::fill

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basic_ios::init

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basic_ios::set_rdbuf

 

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())

Parameters

other

-

another stream to use as source

Return value

*this

Notes

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.

Example

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";
}

Output:

Hello, world