<iostream> Support

The following stream operators are available and work similarly to the built-in integer types.

#include <boost/int256/iostream.hpp>
namespace boost {
namespace int256 {

template <typename charT, typename traits>
std::basic_ostream<charT, traits>& operator<<(std::basic_ostream<charT, traits>& os, const uint256& v);

template <typename charT, typename traits>
std::basic_istream<charT, traits>& operator>>(std::basic_istream<charT, traits>& is, uint256& v);

template <typename charT, typename traits>
std::basic_ostream<charT, traits>& operator<<(std::basic_ostream<charT, traits>& os, const int256& v);

template <typename charT, typename traits>
std::basic_istream<charT, traits>& operator>>(std::basic_istream<charT, traits>& is, int256& v);

} // namespace int256
} // namespace boost

These are host-only functions: they are not annotated with BOOST_INT256_HOST_DEVICE and are not available in device code.

Sign, Base Prefix and showpos

int256 is sign-magnitude in every base: on output, the sign (if any) is written first, before any base prefix from showbase, so -0xff and -0377, never 0x-ff. std::showpos prints a leading + for a non-negative int256 in decimal only; it has no effect in hex or oct mode, and it has no effect on uint256 at all, matching the built-in unsigned types.

On extraction, operator>> accepts an optional leading - before the digits (and before a 0x or 0 prefix, when the active base allows one) but rejects a leading +, matching from_chars. A value outside int256’s range, including one whose magnitude overflows during the parse, sets `failbit.

Flags

The following flags from <ios> are honored. The base flags (std::oct, std::dec, std::hex) affect both input and output; the remaining flags affect output only.

  • std::oct - Octal numbers (input and output)

  • std::dec - Decimal numbers (input and output)

  • std::hex - Hexadecimal numbers (input and output)

  • std::uppercase - Uppercase hexadecimal digits on output (e.g. FFFF)

  • std::nouppercase - Lowercase hexadecimal digits on output (e.g. ffff)

  • std::showbase - Adds a leading base prefix for hex or oct numbers on output (e.g. 0xffff)

  • std::noshowbase - Omits the leading base prefix on output (e.g. ffff)

The width and fill manipulators (std::setw, std::setfill) work with std::left, std::right, and std::internal exactly as they do for the built-in integer types: std::left and std::right pad before or after the whole output (sign and base prefix included), while std::internal places the fill between the sign/prefix and the digits. std::setw(12) << std::internal << std::hex << std::showbase << int256{-255} prints "-0x ff", not "-0xff " (std::left) or " -0xff" (std::right). The internal buffer is sized for the longest possible output, which is 256 characters in base 2.

On extraction (operator>>) a leading 0x or 0 base prefix is accepted and consumed for the active base regardless of showbase, and hexadecimal input is parsed case-insensitively. A value that does not fit in a uint256 sets failbit.

See the IO streaming example for usage demonstrations, including the sign, prefix, and showpos rules above.

Edit this Page