Hi,

I would be surprised if this hasn’t been proposed before. Now that we have std::format, I think it’s hard to make an argument for adding anything formatting-related to iostreams.

Cheers,

Jeremy

On Mon, Feb 10, 2025 at 12:01 Javier Estrada via Std-Proposals <std-proposals_at_[hidden]> wrote:

There is a manipulator gap to read/write integer numbers in binary. As you well know, the standard manipulators are std::oct, std::dec, std::hex, which is essentially a format flag onto ios_base::basefield.

Having a dedicated manipulator would close that gap and would eliminate the current "trick" of using  std::bitset. The (abbreviated) example in cppreference .com reads:

#include <bitset>
#include <iostream>

int main()
{
    std::cout << "The number 42 in octal:   " << std::oct << 42 << '\n'
              << "The number 42 in decimal: " << std::dec << 42 << '\n'
              << "The number 42 in hex:     " << std::hex << 42 << '\n';
 
    // Note: there is no I/O manipulator that sets up a stream to print out
    // numbers in binary format (e.g. bin). If binary output is necessary
    // the std::bitset trick can be used:
    std::cout << "The number 42 in binary:  " << std::bitset<8>{42} << '\n'; 

} 

With a std::bin manipulator:

#include <iostream>
#include <sstream>
 
int main()
{

    // This yields 101010 
    std::cout << "The number 42 in binary:  " << std::bin << 42 << '\n';

}

It would also take advantage of other manipulators, like std::setw and std::setfill:

#include <iostream>
#include <sstream>
 
int main()
{
    // This yields 00101010
    std::cout << std::setw(8) << std::setfill('0');
    std::cout << "The number 42 in binary:  " << std::bin << 42 << '\n';
}

Reading binary numbers would also be addressed by the input streams. 

IF this proposal is considered, I see changes in:

- A new bin flag in ios_base::basefield.

- Support for the flag in ios_base::setf, ios_base::unsetf and ios_base::flags member functions.

- Creation of the manipulator (similar to other manipulators) for the different char_traits

- Support for binary parsing for input streams

- Support for binary output for ostreams.

std::ios_base in cppreference.com:

https://en.cppreference.com/w/cpp/io/ios_base

Integer I/O manipulators

https://en.cppreference.com/w/cpp/io/manip/hex

Regards,

—Javier

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