Reading specific column from .csv in C++

Question

I have a .csv file that has around 5 rows and it looks something like this:

"University of Illinois, Chicago","1200, West Harrison","41.3233313","88.221376"

The first column is the name of the building, the second is the address and the third and fourth column represent the latitude and longitude. I want to take only the values in the 3rd and 4th column for every row.

If I use the getline method and separate every entry with , I do not get the desired result. Here is a sample of what I am doing:

ifstream file("Kiosk Coords.csv");
    double latt[num_of_lines];
    double longg[num_of_lines];
    string name;
    string address;
    string latitude;
    string longitude;
    flag = 0;

    while(file.good()){     
            getline(file,name,',');
            getline(file,address,',');
            getline(file,latitude,',');
            getline(file,longitude,'\n');
            //cout<<name<<" "<<address<<" "<<latitude<<" "<<longitude<<endl;
            cout<<longitude<<endl;
    }

For the above given input, I get the following values in the variable if I use my method:

name = "University of Illinois"
address = "Chicago
latitude = "1200"
longitude = "West Harrison,41.3233313,88.221376"

What I specifically want is this:

latitude = "41.3233313"
longitude = "88.221376"

Please help

`"University of Illinois, Chicago"` -- What do you think would happen when this was given to `getline`? It isn't smart enough to figure out that the embedded comma is not to be considered. Either write a true csv parser, or get one of the many ones floating around here and on the web. — PaulMcKenzie, Jan 11 '18 at 03:23
I get that. I was wondering if there was some kind of operator that could separate column wise — Vishesh Chanana, Jan 11 '18 at 03:24
There is no "operator". The only "operator" would be good old fashioned "write a function". — PaulMcKenzie, Jan 11 '18 at 03:25
[You could use something like this](https://stackoverflow.com/questions/1120140/how-can-i-read-and-parse-csv-files-in-c). Your requirements are more than delimiting on the comma -- you have quoted strings that can contain commas, and to properly parse that requires more sophistication. — PaulMcKenzie, Jan 11 '18 at 03:31
I would suggest you change the delimiter of the csv file to a non-conflict one, e.g. '\t'. Never ',' and '.' ! — walter, Jan 11 '18 at 03:51

O'Neil · Accepted Answer · 2018-01-11T04:29:53.700

8

C++14's std::quoted to the rescue:

char comma;
file >> std::quoted(name) >> comma          // name: University of Illinois, Chicago
     >> std::quoted(address) >> comma       // address: 1200, West Harrison
     >> std::quoted(latitude) >> comma      // latitude: 41.3233313
     >> std::quoted(longitude) >> std::ws;  // longitude: 88.221376

DEMO

edited Jan 11 '18 at 04:29

answered Jan 11 '18 at 03:46

O'Neil

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score 2 · Answer 2 · answered Jan 11 '18 at 03:30

I think you have to manually parse it. Given that all elements are wrapped in quotes, you can easily extract them by just looking for the quotes.

Read a whole line then look for a pair quotes, and take the content between them.

std::string str;
std::getline(file, str);
std::vector<std::string> cols;
std::size_t a, b;

a = str.find('\"', 0);
while (true) {
    b = str.find('\"', a + 1);
    if (b != std::string::npos){
        cols.push_back(str.substr(a, b-a));
    }
    a = str.find('\"', b + 1);
}

Results (double quote included):

cols[0]: "University of Illinois, Chicago"
cols[1]: "1200, West Harrison"
cols[2]: "41.3233313"
cols[3]: "88.221376"

Reading specific column from .csv in C++

2 Answers2