Read String Till Flag (C++)

Question

I'm trying to read a string until a ',' character is reached and store what's been read in a new string.

e.g. "5,6"

// Initialise variables.
string coorPair, xCoor, yCoor

// Ask to enter coordinates.
cout << "Input coordinates: ";

// Store coordinates.
cin >> coorPair

// Break coordinates into x and y variables and convert to integers. 
// ?

I also need to store the y value in a separate variable.

What is the best way to do this in C++?

Also, is the best way to validate the input to convert to integers and test the values range?

Possible duplicate of [Most elegant way to split a string?](https://stackoverflow.com/questions/236129/most-elegant-way-to-split-a-string) — vasek, Aug 02 '17 at 05:21
Possible duplicate of https://stackoverflow.com/questions/1894886/parsing-a-comma-delimited-stdstring — cup, Aug 02 '17 at 05:22

suhdonghwi · Accepted Answer · 2017-08-02T05:44:30.273

1

If you have only one comma seperator in string, you can just find where comma first occurs in input and substring input with found position.

Try following:

std::size_t pos = coorPair.find_first_of(","); //Find position of ','
xCoor = coorPair.substr(0, pos); //Substring x position string
yCoor = coorPair.substr(pos + 1); //Substring y position string
int xCoorInt = std::stoi(xCoor); //Convert x pos string to int
int yCoorInt = std::stoi(yCoor); //Convert y pos string to int

edited Aug 02 '17 at 05:44

answered Aug 02 '17 at 05:24

suhdonghwi

955
1
7
20

Thanks, this worked well. I just had to swap pos.substr with coorPair.substr – user6336941 Aug 02 '17 at 05:42
@user6336941 Oops, my bad. – suhdonghwi Aug 02 '17 at 05:43

score 1 · Answer 2 · answered Aug 02 '17 at 05:26

1

The easiest way to do this is to just let operator>> do all the work for you:

int xCoor, yCoor;
char ch;

cout << "Input coordinates: ";

if (cin >> xCoor >> ch >> yCoor)
{
    // use coordinates as needed ...
}
else
{
    // bad input... 
}

answered Aug 02 '17 at 05:26

Remy Lebeau

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31
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770

Samer Tufail · Answer 3 · 2017-08-02T05:38:46.867

0

You can do this by specifying you delimiter and parsing the string

std::string delimiter = ",";

size_t pos = 0;
std::string token;
while ((pos = coorPair.find(delimiter)) != std::string::npos) {
    token = coorPair.substr(0, pos);
    std::cout << token << std::endl;
    coorPair.erase(0, pos + delimiter.length());
}

std::cout << coorPair << endl;

The last token example in {5,6} the {6} would be in the coorPair.

Another way would be to use std::getline as pointed in the comments:

std::string token; 
while (std::getline(coorPair, token, ',')) 
{ 
    std::cout << token << std::endl; 
}

edited Aug 02 '17 at 05:38

answered Aug 02 '17 at 05:21

Samer Tufail

1,835
15
25

1

This would be easier using `std::getline()` with `','` as its delimiter. – Remy Lebeau Aug 02 '17 at 05:28
Could do yes, I thought OP was interested in 'parsing'. – Samer Tufail Aug 02 '17 at 05:30
1

it is still parsing, just letting the STL help, eg: `std::string token; while (std::getline(coorPair, token, ',')) { std::cout << token << std::endl; }` – Remy Lebeau Aug 02 '17 at 05:35

score 0 · Answer 4 · answered Aug 02 '17 at 17:08

http://www.cplusplus.com/reference/string/string/getline/

I would recommend using getline().

Below is a small example of how I use it. It takes the input from a stream, so you can either use an ifstream as an input, or do what I did below and convert the string to a stream.

// input data
std::string data("4,5,6,7,8,9");

// convert string "data" to a stream
std::istringstream d(data);

// output string of getline()
std::string val;

std::string x;
std::string y;
bool isX = true;

char delim = ',';

// this will read everything up to delim
while (getline(d, val, delim)) {
    if (isX) {
        x = val;
    }
    else {
        y = val;
    }
    // alternate between assigning to X and assigning to Y
    isX = !isX;
}

Read String Till Flag (C++)

4 Answers4