Reading multiple lines of strings from a file and storing it in string array in C++

Question

I have a class called StringList consisting of a constructor and a de-structor. What I am shooting for is for the ability of my program to retain its strings in the array even after it is not running. The way i want to do this is to have my constructor function read strings from a file and store them into my string array (str[]). My de-structor will save my current strings into my file. I am having trouble reading and storing from the file when memory is created. I want each word to be one element in the array. For example, in the file that is being read from, the strings are stored as such:

HELLO
MOM
DAD
FOUR
YELLOW

I want each word to be a slot. In other words. str[0] = HELLO, str[1]= MOM, str[2]=DAD and such.

Here is my constructor function:

StringList::StringList()
{
    numberOfStrings=0;
    str = new string[1000000];

ifstream myfile ("Read.txt");
 if (myfile.is_open())
    {
        for (int i = 0; i < 1000000; i++)
        {
            getline(myfile,str[i]);
            numberOfString++;


        }

        myfile.close();
    }


}

Problem here is the for (int i=0; i<100000;i++) line What this did is continue to fill each blank space into the element until it reached 100000. Same if i put i<20, it would read all the contents and add blanks to fill to 20. Is there anyway to fill up to the amount of actual strings in the txt. file?

Answer 1

NumberOfStrings++ is outside of your for loop when you read (i.e. it only gets incremented once). Also please consider using std::vector<std::string> instead of a dynamic array.

Here's a version of your code using std::vector instead of an array:

#include <vector>
#include <fstream>
#include <iostream>
#include <string>

class StringList
{
public:
    StringList(): str(1000000), numberOfStrings(0)
    {
        std::ifstream myfile ("Read.txt");
        if (myfile.is_open())
        {
            for (int i = 0; i < str.size(); i++)
            {
                getline(myfile, str[i]);
                numberOfStrings++;
            }

            myfile.close();
        }
    }

    StringList::~StringList()
    {
        std::ofstream os("Read.txt");
        for (int i = 0; i <numberOfStrings; i++) 
        {
            os << str[i] << std::endl;
        }
    }

private:
    std::vector<std::string> str;
    int numberOfStrings;
};

As you can see the changes are rather minimal.