string_view compatible std::istringstream.

svstream.hpp

/**
 * MIT No Attribution
 *
 * Copyright 2020-2024 Anna Zhukova
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef GIST_GITHUB_COM_ANDREASXP_SVSTREAM_HPP
#define GIST_GITHUB_COM_ANDREASXP_SVSTREAM_HPP

#include <istream>
#include <streambuf>
#include <string_view>

/**
 * string_view-compatible buffer for reading read-only characters from memory.
 * Implements a buffer based on stackoverflow discussions. Written to be used
 * via isviewstream.
 *
 * @warning sviewbuf does not own memory. If the lifetime of the string ends
 * before this buffer, reading from it invokes undefined behavior.
 *
 * @see https://stackoverflow.com/a/13059195
 * @see https://stackoverflow.com/a/46069245
 */
class sviewbuf : public std::streambuf {
private:
	using ios_base = std::ios_base;

protected:
	pos_type seekoff(
		off_type off,
		ios_base::seekdir dir,
		[[maybe_unused]] ios_base::openmode which = ios_base::in | ios_base::out
	) override {
		if (dir == ios_base::cur)
			gbump(off);
		else if (dir == ios_base::end)
			setg(eback(), egptr() + off, egptr());
		else if (dir == ios_base::beg)
			setg(eback(), eback() + off, egptr());
		return gptr() - eback();
	}

	pos_type seekpos(pos_type sp, ios_base::openmode which) override {
		return seekoff(sp - pos_type(off_type(0)), ios_base::beg, which);
	}

public:
	sviewbuf(const char* s, std::size_t count) {
		auto p = const_cast<char*>(s);
		this->setg(p, p, p + count);
	}

	sviewbuf(std::string_view str) : sviewbuf(str.data(), str.size()) {}
};

/**
 * A std::stringstream analog for string_view.
 * Implements a string_view-based input stream based on stackoverflow
 * discussions.
 *
 * @warning isviewstream does not own memory. If the lifetime of the string
 * ends before this stream, reading from it invokes undefined behavior.
 *
 * @see https://stackoverflow.com/a/13059195
 * @see https://stackoverflow.com/a/46069245
 */
class isviewstream : private virtual sviewbuf, public std::istream {
public:
	isviewstream(std::string_view str) : sviewbuf(str), std::istream(static_cast<std::streambuf*>(this)) {}
};

#endif  // GIST_GITHUB_COM_ANDREASXP_SVSTREAM_HPP

What's the license of this?

Thanks for reaching out!
I've updated the code to include the MIT-0 license text.

Thanks.

Thanks for the gist, helped me to improve the performance of some functions that made use of istringstream.
Just one question: I get a warning about 'unused parameter' which in seekoff, is it safe to just ignore it (using [[maybe_unused]])?

Thanks for pointing that out! I updated the gist with your suggestion.