I want to iterate over std::cin, line by line, addressing each line as a std::string. Which is better:
string line;
while (getline(cin, line))
{
// process line
}
or
for (string line; getline(cin, line); )
{
// process line
}
? What is the normal way to do this?
This is based on Jerry Coffin's answer. I wanted to show c++20's std::ranges::istream_view. I also added a line number to the class. I did this on godbolt, so I could see what happened. This version of the line class still works with std::input_iterator.
https://en.cppreference.com/w/cpp/ranges/basic_istream_view
https://www.godbolt.org/z/94Khjz
class line {
std::string data{};
std::intmax_t line_number{-1};
public:
friend std::istream &operator>>(std::istream &is, line &l) {
std::getline(is, l.data);
++l.line_number;
return is;
}
explicit operator std::string() const { return data; }
explicit operator std::string_view() const noexcept { return data; }
constexpr explicit operator std::intmax_t() const noexcept { return line_number; }
};
int main()
{
std::string l("a\nb\nc\nd\ne\nf\ng");
std::stringstream ss(l);
for(const auto & x : std::ranges::istream_view<line>(ss))
{
std::cout << std::intmax_t(x) << " " << std::string_view(x) << std::endl;
}
}
prints out:
0 a
1 b
2 c
3 d
4 e
5 f
6 g