Question

I am looking to access a completely random line of a small text file, and import the same line in another text file in a C++ program. I need to do this fairly simply, I am a beginner to C++ programming. I will include main.cpp. If you need the other .cpp or the .h, just let me know, I will post it.

Main.cpp:

#include <fstream>
#include <iomanip>
#include <iostream>
#include <cmath>
#include <ctime>
#include <string>
#include <vector>

#include "getQuestion.h"

using namespace std;

int main() {
    int mainMenuChoice;
    ifstream Bibliography;
    //string easyBib;
    string easyBib;
    ifstream inputFile;

    cout << "Quiz Menu\n\n";
    cout << "1. Play Game!\n";
    cout << "2. Bibliography\n";
    cout << "3. Developer Info\n";
    //cout << "4. Admin Menu\n";
    cout << "4. Exit\n";
    cout << "Menu Choice: ";
    cin >> mainMenuChoice;

    switch (mainMenuChoice) {
    case 1:
        //int getQuestion(string Q,A);
        //cout << Q;
        break;
    case 2:
        inputFile.open("Bib.rtf");
        inputFile >> easyBib;
        cout << easyBib << endl;
        break;
    case 3:
        cout << "Program made by: XXXX XXXXXXXX" << endl;
        cout << "XXX. XXXXXXX'X Period 4 Social Studies Class" << endl;
        break;
    /*case 4:
        break;*/
    case 4:
        cout << "Thank you for playing!" << endl;
        return(0);
    default:
        cout << "Sorry, Invalid Choice!\n";
        return(0);
    }
    return(0);
}

Answer 1

The easiest solution would be to read the entire file line by line (using getline) into a vector<string>. Then it’s trivial to select a random element from that vector.

You can read a line from an input stream like this:

string line;
getline( inputFile, line );

It returns a reference to the stream, which can be tested directly for error. So this is easily turned into a loop like this:

vector<string> lines;
for( string line; getline(inputFile,line); )
{
    lines.push_back(line);
}

Now you can use the size function of vector to determine how many lines you have read, and then choose a random one.

size_t iRandLine = rand() % lines.size();
string randomLine = lines[iRandLine];
cout << "Line " << (iRandLine+1) << ": " << randomLine << endl;

Of course, you need to know that there will be fewer than RAND_MAX lines in your file. Otherwise you’ll have to combine multiple calls to rand just to cover the range.