Is there a way to extract certain info from a string? c++ - c++

Question

I need to read in some lines from a text file (amount of lines will be known during run time) but an example could be something like this:
Forecast.txt:
Day 0:S
Day 3:W
Day 17:N
My idea was to create a class which I did:
class weather
{
int day;
char letter;
};
Then create a vector of class as so:
vector<wather>forecast;
and now here is where I'm stuck. So I think I'd use a while loop?
id use my ifstream to read the info in and use a string to hold the information im reading in.
What I want to do is read in each line and extract the day number so in this example the 0, 3 and 15 and get the letter so S, W, N and store it in the vector of the class.
I was wondering if there's any way to do that? I could be coming at this wrong so forgive me im new to c++ and trying to figure this out.
Thank you for helping!

Answer 1

Your can use std::istringstream to parse each line, eg:
#include <sstream>
while (getline(in_s1, lines2))
{
istringstream iss(lines2);
string ignore1; // "Day"
char ignore2; // ":"
forecast f;
if (iss >> ignore1 >> f.day >> ignore2 >> f.letter)
weather.push_back(f);
}
Live Demo
Alternatively, you can parse each line using std::regex and related classes.

Answer 2

istringstream and the >> operator is probably the neatest C++ way to do it, as described in Remy's answer. In case you prefer to be a little less reliant on the stream magic and a bit more explicit, you can find the tokens you need and then extract them directly from the string.
Something like this:
while (getline(in_s1, lines2))
{
size_t startPos = lines2.find(' '); //get position of the space before the day
size_t endPos = lines2.find(':', startPos); //get position of the colon after the day
string day = lines2.substr (startPos+1, endPos-startPos-1); //extract the day
forecast f;
f.day = stoi(day); //stoi only supported since C++11, otherwise use atoi
f.letter = lines2[endPos+1];
weather.push_back(f);
}