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/* This file provides a variant of std::istringstream that doesn't
copy its string argument. This is useful for large strings. The
caller must ensure that the string object is not destroyed while
it's referenced by this object. */
#pragma once
#include <iostream>
#include <string>
template <class CharT, class Traits = std::char_traits<CharT>,
class Allocator = std::allocator<CharT>>
class basic_istringbuf_nocopy : public std::basic_streambuf<CharT, Traits> {
public:
using string_type = std::basic_string<CharT, Traits, Allocator>;
using off_type = typename std::basic_streambuf<CharT, Traits>::off_type;
using pos_type = typename std::basic_streambuf<CharT, Traits>::pos_type;
using int_type = typename std::basic_streambuf<CharT, Traits>::int_type;
using traits_type = typename std::basic_streambuf<CharT, Traits>::traits_type;
private:
const string_type& s;
off_type off;
public:
explicit basic_istringbuf_nocopy(const string_type& s) : s{s}, off{0} {}
private:
pos_type seekoff(off_type off, std::ios_base::seekdir dir,
std::ios_base::openmode which) {
if (which & std::ios_base::in) {
this->off =
dir == std::ios_base::beg
? off
: (dir == std::ios_base::end ? s.size() + off : this->off + off);
}
return pos_type(this->off);
}
pos_type seekpos(pos_type pos, std::ios_base::openmode which) {
return seekoff(pos, std::ios_base::beg, which);
}
std::streamsize showmanyc() { return s.size() - off; }
int_type underflow() {
if (typename string_type::size_type(off) == s.size()) {
return traits_type::eof();
}
return traits_type::to_int_type(s[off]);
}
int_type uflow() {
if (typename string_type::size_type(off) == s.size()) {
return traits_type::eof();
}
return traits_type::to_int_type(s[off++]);
}
int_type pbackfail(int_type ch) {
if (off == 0 || (ch != traits_type::eof() && ch != s[off - 1])) {
return traits_type::eof();
}
return traits_type::to_int_type(s[--off]);
}
};
template <class CharT, class Traits = std::char_traits<CharT>,
class Allocator = std::allocator<CharT>>
class basic_istringstream_nocopy : public std::basic_iostream<CharT, Traits> {
using buf_type = basic_istringbuf_nocopy<CharT, Traits, Allocator>;
buf_type buf;
public:
explicit basic_istringstream_nocopy(const typename buf_type::string_type& s)
: std::basic_iostream<CharT, Traits>(&buf), buf(s){};
};
using istringstream_nocopy = basic_istringstream_nocopy<char>;
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