std::basic_ios::copyfmt - cppreference.com

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# std::basic_ios::copyfmt

From cppreference.com
< cpp‎ | io‎ | basic ios

basic_ios& copyfmt(const basic_ios& other); |  |

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())

### [edit] Parameters

other | - | another stream to use as source

### [edit] Return value

*this

### [edit] 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.

### [edit] 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

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