seqan3::detail::fast_ostreambuf_iterator< char_t, traits_t > Class Template Reference

Functionally the same as std::ostreambuf_iterator, but offers writing a range more efficiently. More...

#include <seqan3/io/stream/detail/fast_ostreambuf_iterator.hpp>

Public Types
Associated types
using	difference_type = ptrdiff_t
	Defaults to ptrdiff_t.
using	value_type = char_t
	The char type of the stream.
using	reference = char_t
	The char type of the stream.
using	pointer = void
	Has no pointer type.
using	iterator_category = std::output_iterator_tag

Public Member Functions
bool	failed () const noexcept
	Returns true if this iterator has encountered the end-of-file condition on output,false` otherwise.
fast_ostreambuf_iterator &	operator* ()
	no op.
fast_ostreambuf_iterator &	operator= (char_t const c)
	Writes a character to the associated output stream.
void	write_end_of_line (bool const add_cr)
	Write "\n" or "\r\n" to the stream buffer, depending on arguments.
template<typename number_type > requires std::is_arithmetic_v<number_type>
auto	write_number (number_type num)
	Writes a number to the underlying stream buffer using std::to_chars.
template<std::ranges::forward_range range_type> requires std::ranges::borrowed_range<range_type>
auto	write_range (range_type &&rng)
	Writes a range to the associated output.
Constructors, destructor and assignment
	fast_ostreambuf_iterator () noexcept=default
	Defaulted.
	fast_ostreambuf_iterator (fast_ostreambuf_iterator const &) noexcept=default
	Defaulted.
	fast_ostreambuf_iterator (fast_ostreambuf_iterator &&) noexcept=default
	Defaulted.
fast_ostreambuf_iterator &	operator= (fast_ostreambuf_iterator const &) noexcept=default
	Defaulted.
fast_ostreambuf_iterator &	operator= (fast_ostreambuf_iterator &&) noexcept=default
	Defaulted.
	~fast_ostreambuf_iterator () noexcept=default
	Defaulted.
	fast_ostreambuf_iterator (std::basic_streambuf< char_t, traits_t > &ibuf)
	Construct from a stream buffer.
Arithmetic operators
fast_ostreambuf_iterator &	operator++ ()
	no op.
fast_ostreambuf_iterator &	operator++ (int)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Private Attributes
stream_buffer_exposer< char_t, traits_t > *	stream_buf = nullptr
	Down-cast pointer to the stream-buffer.

Detailed Descriptionno-api

template<typename char_t, typename traits_t = std::char_traits<char_t>>
class seqan3::detail::fast_ostreambuf_iterator< char_t, traits_t >

Functionally the same as std::ostreambuf_iterator, but offers writing a range more efficiently.

Template Parameters

char_t	The stream's character type.
traits_t	The stream's traits type.

The functions seqan3::fast_ostreambuf_iterator::write_range and seqan3::fast_ostreambuf_iterator::write_n allow more efficient writing of ranges by writing in chunks that avoiding overflow checks.

// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: CC0-1.0
 
#include <sstream>
 
#include <seqan3/io/stream/detail/fast_ostreambuf_iterator.hpp>
 
int main()
{
    std::string id{"seq1"};
    std::string sequence{"ACTGACTGACTGACTAGCATGACTAGCATGC"};
 
    // construct iterator from stream buffer
    std::ostringstream ostr{};
    auto stream_it = seqan3::detail::fast_ostreambuf_iterator{*ostr.rdbuf()};
 
    // You can do anything you could do with a regular std::ostreambuf_iterator
    stream_it = '>';  // writes '>' to stream
    *stream_it = ' '; // writes ' ' to stream
 
    // Additionally, there is an efficient write_range member function
 
    // Example 1: Write a range completely
    stream_it.write_range(id); // return value can be ignored
 
    // Example 2: Write a range in chunks of 10
    auto it = std::ranges::begin(sequence);
    while (it != std::ranges::end(sequence))
    {
        /* Note that you need cannot use stream_it.write_range(rng | std::views::take(10)) here
         * because the returned iterator is not of the correct type.
         */
        auto current_end = it;
        size_t steps = std::ranges::advance(current_end, 10u, std::ranges::end(sequence));
        using subrange_t =
            std::ranges::subrange<decltype(it), decltype(current_end), std::ranges::subrange_kind::sized>;
        // Be aware that your range_type must model std::ranges::borrowed_range in order to use the return value!
        it = stream_it.write_range(subrange_t{it, current_end, 10u - steps});
        stream_it = ' ';
    }
}

Member Typedef Documentation

iterator_category [no-api]

using seqan3::detail::fast_ostreambuf_iterator< char_t, traits_t >::iterator_category = std::output_iterator_tag

no-api

Pure output iterator.

Member Function Documentation

write_number() [no-api]

template<typename char_t , typename traits_t = std::char_traits<char_t>>

template<typename number_type >
requires std::is_arithmetic_v<number_type>

auto seqan3::detail::fast_ostreambuf_iterator< char_t, traits_t >::write_number ( number_type  num )

no-apiinline

Writes a number to the underlying stream buffer using std::to_chars.

Template Parameters

number_type

The type of number; must model seqan3::arithmetic.

Parameters

[in]

num

The number to write.

write_range() [no-api]

template<typename char_t , typename traits_t = std::char_traits<char_t>>

template<std::ranges::forward_range range_type>
requires std::ranges::borrowed_range<range_type>

auto seqan3::detail::fast_ostreambuf_iterator< char_t, traits_t >::write_range ( range_type &&  rng )

no-apiinline

Writes a range to the associated output.

Template Parameters

range_type

The type of range to write; Must model std::ranges::forward_range.

Parameters

[in]

rng

The range to write.

Returns

If range_type models std::ranges::borrowed_range returns an iterator pointing to end of the range (rng) else returns void.

This function avoids the buffer-at-end check by writing the range in chunks, where a chunks has the size of the remaining space in the put area of the buffer. If the range type models std::ranges::sized_range the chunks are written using std::ranges::copy_n, which may use memcpy if applicable. Otherwise, a simple for loop iterates over the chunk.

Attention

You can only use the return value (end iterator) if your range type models std::ranges::borrowed_range.

Example:

// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: CC0-1.0
 
#include <sstream>
 
#include <seqan3/io/stream/detail/fast_ostreambuf_iterator.hpp>
 
int main()
{
    std::string id{"seq1"};
    std::string sequence{"ACTGACTGACTGACTAGCATGACTAGCATGC"};
 
    // construct iterator from stream buffer
    std::ostringstream ostr{};
    auto stream_it = seqan3::detail::fast_ostreambuf_iterator{*ostr.rdbuf()};
 
    // You can do anything you could do with a regular std::ostreambuf_iterator
    stream_it = '>';  // writes '>' to stream
    *stream_it = ' '; // writes ' ' to stream
 
    // Additionally, there is an efficient write_range member function
 
    // Example 1: Write a range completely
    stream_it.write_range(id); // return value can be ignored
 
    // Example 2: Write a range in chunks of 10
    auto it = std::ranges::begin(sequence);
    while (it != std::ranges::end(sequence))
    {
        /* Note that you need cannot use stream_it.write_range(rng | std::views::take(10)) here
         * because the returned iterator is not of the correct type.
         */
        auto current_end = it;
        size_t steps = std::ranges::advance(current_end, 10u, std::ranges::end(sequence));
        using subrange_t =
            std::ranges::subrange<decltype(it), decltype(current_end), std::ranges::subrange_kind::sized>;
        // Be aware that your range_type must model std::ranges::borrowed_range in order to use the return value!
        it = stream_it.write_range(subrange_t{it, current_end, 10u - steps});
        stream_it = ' ';
    }
}

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The documentation for this class was generated from the following file:

• fast_ostreambuf_iterator.hpp