Just quick one, how should I go about printing a value from a struct? the 'winningnums' contains a string from another function (edited down for minimal example)

I've tried the below but the program doesnt output anything at all, is my syntax incorrect?

 struct past_results {
       std::string date;
       std::string winningnums;
    };

int main(){

    past_results results;

    std::cout << results.winningnums;
     
    return 0;
}

EDIT:

just to give some more insight, here's the function that populates my struct members. Is it something here im doing wrong?

 //function to read csv
void csv_reader(){
    std::string line;
    past_results results;
    past_results res[104];
    

    int linenum = 0;  



    //open csv file for reading
    std::ifstream file("Hi S.O!/path/to/csv", std::ios::in);
    if(file.is_open()) 
    {
       
        while (getline(file, line))
        {
            std::istringstream linestream(line);
            std::string item, item1;
    
            //gets up to first comma
            getline(linestream, item, ',');
            results.date = item;
    
            //convert to a string stream and put into winningnums
            getline(linestream, item1);
            results.winningnums = item1;
    
            //add data to struct
            res[linenum] = results;

            linenum  ;
        }
    }
      
    //display data from struct
    for(int i = 0; i < linenum; i  ) {
        std::cout << "Date: " << res[i].date << " \\\\ Winning numbers: " << res[i].winningnums << std::endl;
    }  

}

CodePudding user response：

Your example doesn't initialize the struct members. There is no data to print, so why would you expect it to output anything?

CodePudding user response：

is my syntax incorrect?

No, it's just fine and if you add the inclusion of the necessary header files

#include <iostream>
#include <string>

then your whole program is ok and will print the value of the default constructed std::string winningnums in the results instance of past_results. A default constructed std::string is empty, so your program will not produce any output.

Your edited question shows another problem. You never call csv_reader() and even if you did, the result would not be visible in main() since all the variables in csv_reader() are local. Given a file with the content:

today,123
tomorrow,456

and if you call csv_reader() from main(), it would produce the output:

Date: today \\ Winning numbers: 123
Date: tomorrow \\ Winning numbers: 456

but as I mentioned, this would not be available in main().

Here's an example of how you could read from the file and make the result available in main(). I've used a std::vector to store all the past_results in. It's very practical since it grows dynamically, so you don't have to declare a fixed size array.

#include <fstream>
#include <iostream>
#include <sstream>  // istringstream
#include <string>   // string
#include <utility>  // move
#include <vector>   // vector

struct past_results {
    std::string date;
    std::string winningnums;
};

// added operator to read one `past_results` from any istream
std::istream& operator>>(std::istream& is, past_results& pr) {
    std::string line;

    if(std::getline(is, line)) {
        std::istringstream linestream(line);

        if(!(std::getline(linestream, pr.date, ',') &&
             std::getline(linestream, pr.winningnums)))
        { // if reading both fields failed, set the failbit on the stream
            is.setstate(std::ios::failbit);
        }
    }
    return is;
}

std::vector<past_results> csv_reader() { // not `void` but returns the result
    std::vector<past_results> result; // to store all past_results read in

    // open csv file for reading
    std::ifstream file("csv"); // std::ios::in is default for an ifstream
    if(file) {
        // loop and read records from the file until that fails:
        past_results tmp;
        while(file >> tmp) {   // this uses the `operator>>` we added above
            // and save them in the `result` vector:
            result.push_back(std::move(tmp));
        }
    }

    return result; // return the vector with all the records in
}

int main() {
    // get the result from the function:
    std::vector<past_results> results = csv_reader();

    // display data from all the structs
    for(past_results& pr : results) {
        std::cout << "Date: " << pr.date
                  << " \\\\ Winning numbers: " << pr.winningnums << '\n';
    }
}