C++ program to read an input file with multiple headers

[Joon]

Homework Statement

Write a program that can read an input file with a simple header.

The Attempt at a Solution

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

int main() {

    ifstream inFile;
    inFile.open("Data");    //Check for error
    if (inFile.fail()) {

        cout << "Sorry, the file could not be opened." << "\n";
        exit(1);

    }

    string c;
    double x, y;
  

    return 0;
}

<< Mentor Note -- added Code tags for readability >>

I'm not sure what to do next, would appreciate your help.

 

[DrClaude]

How do you read in data from a file?

If the header is not needed, then you can simply start by reading a line and not do anything about its content.

 

[Mark44]

Homework Statement

Write a program that can read an input file with a simple header.

The Attempt at a Solution

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

int main() {

    ifstream inFile;
    inFile.open("Data");    //Check for error
    if (inFile.fail()) {

        cout << "Sorry, the file could not be opened." << "\n";
        exit(1);

    }

    string c;
    double x, y;
 

    return 0;
}

<< Mentor Note -- added Code tags for readability >>

I'm not sure what to do next, would appreciate your help.

It appears your program won't be able to open the file. In your attachment, the filename appears to be Data.txt, but your program is attempting to open a file named Data, with no file suffix.

Since you have access to the data file, you know how it is formatted. Your program needs to read the first line (the header line) and discard it. For each succeeding line, a loop in the program needs to read a character and two doubles. The loop should exit when no more lines can be read.

 

[Joon]

Yes it should be Data.txt. Was a mistake.

How do you read the first line of the file then discard it? I really have no idea. It's only been several weeks since I started learning C++.
Does it have to do with getline function?
Thanks.

 

[Mark44]

Yes it should be Data.txt. Was a mistake.

How do you read the first line of the file then discard it? I really have no idea. It's only been several weeks since I started learning C++.
Does it have to do with getline function?
Thanks.

Yes, you could use getline. Just read it into a "junk" variable that you don't use.
For the other lines, you know that they contain a character (which you don't need to keep) and two doubles.

What are you supposed to do with the numbers in the file?

 

[Joon]

The only task is to write a program that can read the input file.
I have tried to modify the code as follows, please let me know what went wrong.

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

int main() {

    ifstream inFile;
    inFile.open("Data.txt");
    string line, c;
    double x, y;
 
    getline(inFile, line);
    if (inFile.is_open())
    {
        while (inFile >> c >> x >> y)
            cout << c << " " << x << " " << y << "\n";
        inFile.close();
    }

    //Check for error
    if (inFile.fail()) {

        cout << "Sorry, the file could not be opened." << "\n";
        exit(1);

    }
    return 0;
}

 

[Joon]

This is another code that I wrote. Is this any better than the 1st one above? Thanks.

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

int main() {

    ifstream inFile("Data.txt");
    string line, c;
    double x, y;

    getline(inFile, line);

    if (inFile.is_open())
    {
        while (inFile >> c >> x >> y)
        {
            cout << c << "" << x << "" << y << "\n";
        }
        inFile.close();
    }

    else
        cout << "The file could not be opened." << "\n";
    cin.get();
    return 0;
}

 

[Mark44]

This is another code that I wrote. Is this any better than the 1st one above? Thanks.

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

int main() {

    ifstream inFile("Data.txt");
    string line, c;
    double x, y;

    getline(inFile, line);                                              // 1

    if (inFile.is_open())
    {
        while (inFile >> c >> x >> y)
        {
            cout << c << "" << x << "" << y << "\n";         // 2
        }
        inFile.close();
    }

    else
        cout << "The file could not be opened." << "\n";
    cin.get();
    return 0;
}

I added code tags to both of your posts. They're easy to use. Just surround your code like what I did below. When you use the code tags, you won't see them in the code that is displayed in the browser.
[code=c]
<your code>
[/code]
Comments.- I've added numbered comments in your code to go with what I've written below.
1. The call to getline() should be in the body of the if statement. You don't want to try to get a line if you can't open the file.
2. It's hard to see, but it looks like you are outputting empty strings between c and x and y. Put at least one space between the pairs of quotes. IOW, like this " ", not this "".

Otherwise it looks OK.

 

[Joon]

Thanks for your corrections.
I have run the code after changing the things you mentioned, but it just says "The file could not be opened."
I am not sure what the reason is. What do you think is the problem?

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

int main() {

    ifstream inFile("Data.txt");
    string line, c;
    double x, y;

  

    if (inFile.is_open())
    {
        getline(inFile, line);
        while (inFile >> c >> x >> y)
        {
            cout << c << " " << x << " " << y << "\n";
        }
        inFile.close();
    }

    else
        cout << "The file could not be opened." << "\n";
    cin.get();
    return 0;
}

 

[Mark44]

I have run the code after changing the things you mentioned, but it just says "The file could not be opened."
I am not sure what the reason is. What do you think is the problem?

Could be a couple of things. Make sure the filename is actually Data.txt and not with some other file extension.

Some compilers, such as MSFT Visual Studio, look in different directories, depending on whether you're running in the debugger or are running an executable (.exe extension). If you're running your code from within the debugger, the input file should be in the same directory as the source code file.

Also, in the debugger, see what value is returned by is_open(). I forget what the return values are, but check the documentation, and it will say that it returns 1 (or true) if the file is open, and 0 or some other value if the file can't be opened or can't be found.

 

[Joon]

I have moved the source file into the same file as the input file. In my case, my laptop file -> source -> repos. Now both the data file and code file are in the repos file. I am using Visual Studio 2017.
The filename is not actually Data.txt but is a text file ending with .txt, so I don't think it is a problem.
I have run the code again but still says the file could not be opened.

I'm trying to see what return value is, what do I need to do exactly with is_open()?
Thank you.

 

[Joon]

Or should I move the text file into Project 2? Project 2 is the one where the code was written on.
From repos -> project 2 -> project 2. Please refer to the pictures attached.

 

[Mark44]

I have moved the source file into the same file as the input file.

No, don't do that. Move the text file into the same directory as the source code, not the other way around.

From your attached images, it looks like your project is named Project2. The file hierarchy that Vis. Studio sets up probably looks like this:

Project2
... Project2
...Debug
The outer Project2 directory contains a file that Visual Studio uses, with a file extension of .sln, plus the two directories shown above.
The inner Project2 directory contains your source code file (with .cpp extension) and several other files that VS uses, with extensions of .vxproj, .vxproj.user, and vxproj.filters. If you run your program from within Vis. Studio, that's where your input file should be.

Last, the Debug directory contains an executable that you can run from a command prompt window, outside of Visual Studio.

 

[Joon]

Yes, I meant I put the text file into the same directory as the source code. Don't know why I wrote the other way around.
I have now placed the text file in the correct place (I had placed it in the outer directory before) and now the code works!
Thank you for your help.

I've got another question though, what do I need to do if I want to read the text file excluding the alphabets shown on the very left side?

 

[Mark44]

I've got another question though, what do I need to do if I want to read the text file excluding the alphabets shown on the very left side?

In your while loop, you have this condition:

inFile >> c >> x >> y

Your code is reading c, x, and y. You can just not do anything with c; you're basically just discarding it.[/code]

 

[Joon]

Right, that's all my questions answered.
Thank you again and hope you have a nice day.