C++ problems reading input file and outputting into an output file using getline()

Question

I have this assignment for an intro C++ class and I'm confused as to why my getline seems to be working but it doesn't output my functions into the outfile.txt.My teacher said my getline syntax is incorrect, but I'm confused as to how. My infile.txt reads:

T & 4
S @ 6
T x 5
R * 5 7
D $ 7
D + 5
R = 4 3
E

And my code:

#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;


void draw_rect (char out_char, int rows, int columns); // Draws a rectangle shape

void draw_square (char out_char, int rows); //Draws a square shape

void draw_triangle (char out_char, int rows);// Draws a triangle shape

void draw_diamond (char out_char, int rows); // Draws a diamond shape

int main()
{
    ofstream outfile;
    ifstream infile;
    int row, col;
    bool exit = false;
    char value;
    infile.open("infile.txt");
    outfile.open("outfile.txt");
    if(!infile.good())
    {
        cout << "failed to open\n";
    }else
    {
        string buffer;
        while(!infile.eof() || !exit)
        {
            getline(infile, buffer);
                switch(buffer[0])
                {
                case 'R':
                   value = buffer[2];
                   row = buffer[4];
                   col = buffer[6];
                   draw_rect(value, row, col);
                   break;
                case 'T':
                    value = buffer[2];
                    row = buffer [4];
                    draw_triangle(value, row);
                    break;
                case 'D':
                    value = buffer[2];
                    row = buffer[4];
                    draw_diamond(value, row);
                    break;
                case 'S':
                    value = buffer[2];
                    row = buffer[4];
                    draw_square(value, row);
                    break;
                case 'E':
                    cout << "Files Written.\nExiting." << endl;
                    exit = true;
                    break;
                default:
                    cout << "Invalid input, try again" << endl;
                }
        }
    }
    return  0;

}

void draw_diamond (char out_char, int rows)
{
    ofstream outfile;
    int space = 1;
    space = rows - 1;
    for (int i = 1; i <= rows; i++)
    {
        for (int k = 1; k <= space; k++)
        {
            outfile << " ";
        }
        space--;
        for( int k = 1; k <= 2*i-1; k++)
        {
            outfile << out_char;
        }
        outfile << endl;
    }
    space = 1;
    for (int i = 1; i <= rows; i++)
    {
       for(int k = 1; k <= space; k++)
       {
           outfile << " ";
       }
       space++;
       for(int k = 1; k <= 2*(rows-i)-1; k++)
       {
           outfile << out_char;
       }
       outfile << endl;
    }
}

void draw_triangle (char out_char, int rows)
{
    ofstream outfile;
     for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j <= i; j++)
        {
            outfile << out_char;
        }
        outfile << endl;
}
}

void draw_square (char out_char, int rows)
{
    ofstream outfile;
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < rows; j++)
        {
            outfile << out_char;
        }
        outfile << endl;
    }
}

void draw_rect (char out_char, int rows, int columns)
{
    ofstream outfile;
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < columns; j++)
        {
            outfile << out_char;
        }
        outfile << endl;
    }
}

Answer 1

Using one of your functions as an example:

void draw_rect (char out_char, int rows, int columns)
{
    ofstream outfile;

This declares a new std::ofstream object in your draw_rect() function. draw_rect() does not open this std::ofstream object, so this draw_rect()'s attempts to writing anything into this outfile does absolutely nothing.

The fact that you created an std::ofstream object with the same name in your main(), that you did open, means absolutely nothing. Just because you have the same object with the same name in different functions doesn't mean that they are the same object. C++ does not work this way.

You need to change your main() function to pass its outfile into each function, by reference, as a parameter, instead of declaring another object with the same name in each function. The above function would be, for example:

void draw_rect (ofstream &outfile, char out_char, int rows, int columns)
{

You will need to change each one of your functions to receive the outfile parameter by reference, like that, change their forward declarations, and explicitly pass outfile as a first parameter from main(), in each function call.

Finally, regarding your claim that your teacher told you that there was something wrong with your usage of getline:

You were fully justified with your confusion. If your "getline syntax is incorrect" then you would've gotten a compilation failure. Since your question did not mention any compilation errors, even before investigating and determine the actual issue, it was possible to reasonably conclude that: 1) the getline syntax was correct, 2) the program compiled, and 3) you need to find a better teacher, if your intentions are to actually learn C++ without being hampered by bad instructors.

From all appearances, your issue had nothing to do with getline. Your teacher was simply incompetent, and doesn't really know much about C++. That's not your fault, of course, but you need to understand that.

P.S.:

while(!infile.eof() || !exit)

This is a small bug. In this case the bug is hidden, because eventually exit gets set with your sample input, correctly, but you should fix this after reading and understanding the explanation given at this link.