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

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:

# Declarations

basic_ios& copyfmt( const basic_ios& other );

# 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 I/O state savers library for the same purpose.

# Example

#include <bitset>
#include <climits>
#include <fstream>
#include <iostream>
 
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";
 
    auto bin = [](std::ios_base::fmtflags f)
    {
        return std::bitset<sizeof(std::ios_base::fmtflags) * CHAR_BIT>
            { static_cast<unsigned long long>(f) };
    };
    std::ofstream out2;
    std::cout << "1) out2.flags(): " << bin(out2.flags()) << '\n';
    std::cout << "2) cout.flags(): " << bin(std::cout.flags()) << '\n';
    std::cout.setf(std::ios::hex | std::ios::fixed | std::ios::boolalpha);
    std::cout << "3) cout.flags(): " << bin(std::cout.flags()) << '\n';
    out2.copyfmt(std::cout); // copy everything except rdstate and rdbuf
    std::cout << "4) out2.flags(): " << bin(out2.flags()) << '\n';
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 256	C++98	step 3 called the registered callbacks with theevent type copy_event, which is not defined	corrected tocopyfmt_event
LWG 292	C++98	if other refers to the same object as *this, the member objectswere still copied and the registered callbacks were still called	do nothingin this case