Read in data from text file line by line, separated by multiple delimiters in C++

Question

I have data in a text file which I wish to read in and split up to then create a new object out of.

I have found this code:

std::ifstream file("plop");
std::string   line;

while(std::getline(file, line))
{
    std::stringstream   linestream(line);
    std::string         data;
    int                 val1;
    int                 val2;

    std::getline(linestream, data, '\t');

    linestream >> val1 >> val2;
}

Which reads in a text document and splits it by line. However this code assumes the delimiter is always a tab. What if the data had more than one delimiter which would point to what type of data would follow it. i.e assuming a text file such as:

hey, "hi" (hello) [hola]
bye, "by" (byeee) [biii]

and I wanted to split the data into

String twoCharacters;
String threeCharacters;
String fourCharacters;
String fiveCharacters;

so

twoCharacters = hi and by

with the delimiter being two " and

threeCharacters = hey and bye

with the delimiter being a , after it

Any help would be greatly appreciated! Thanks.

Answer 1

You can just keep calling std::getline() with different delimiters:

std::ifstream file("test.txt");

std::string   line;
while(std::getline(file, line))
{
    std::stringstream linestream(line);

    std::string skip;
    std::string item1;
    std::string item2;
    std::string item3;
    std::string item4;

    std::getline(linestream, item1, ',');
    std::getline(linestream, skip, '"');
    std::getline(linestream, item2, '"');
    std::getline(linestream, skip, '(');
    std::getline(linestream, item3, ')');
    std::getline(linestream, skip, '[');
    std::getline(linestream, item4, ']');

    if(linestream) // true if there were no errors reading the stream
    {
        std::cout << item1 << '\n';
        std::cout << item2 << '\n';
        std::cout << item3 << '\n';
        std::cout << item4 << '\n';
    }
}

I used variable skip to read up to the beginning of the next field.

Answer 2

You could use a std::istream::sentry to do this. While a little complicated, you're given almost complete control over how your data is input.

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>
#include <map>

std::istream& operator>>(std::istream& is,
        std::map<std::string, std::vector<std::string> >& map) {
    std::istream::sentry s(is);
    if(s) {
        // your accumulator
        std::string str1;
        // while your stream is good keep appending data
        while(is.good()) {
            // get the next character in the stream
            char c = is.get();
            // if it is a comma append the data to the "three" vector
            if(c == ',') {
                map["three"].push_back(str1);
            // if it is a comma get all of the data until the next comma
            } else if(c == '"') {
                std::string str2;
                str2 += c;
                c = is.get();
                while(c != '"') {
                    str2 += c;
                    c = is.get();
                }
                str2 += c;
                map["two"].push_back(str2);
            // do the same thing for parenthases
            } else if(c == '(') {
                std::string str2;
                str2 += c;
                c = is.get();
                while(c != ')') {
                    str2 += c;
                    c = is.get();
                }
                str2 += c;
                map["five"].push_back(str2);
            // do the same thing for square brackets
            } else if(c == '[') {
                std::string str2;
                str2 += c;
                c = is.get();
                while(c != ']') {
                    str2 += c;
                    c = is.get();
                }
                str2 += c;
                map["four"].push_back(str2);
            // append to your accumulator if you get an alphanumeric char
            } else if(std::isalnum(c)) {
                str1 += c;
            // clear your accumulator if you get a return
            } else if(c == '\n') {
                str1.clear();
            }
        }
    }
    return(is);
}

int main() {
    std::ifstream file("plop");
    // make your map to hold your data
    std::map<std::string, std::vector<std::string> > map;
    map["two"] = std::vector<std::string>();
    map["three"] = std::vector<std::string>();
    map["four"] = std::vector<std::string>();
    map["five"] = std::vector<std::string>();

    // read your data
    file >> map;

    // print your data
    std::vector<std::string> words{"two", "three", "four", "five"};

    for(auto x: words) {
        std::cout << x << std::endl;
        for(auto y: map[x]){
            std::cout << '\t' << y << std::endl;
        }
    }
}

This should print

two
    "hi"
    "by"
three
    hey
    bye
four
    [hola]
    [biii]
five
    (hello)
    (byeee)