(C++) Why are additional blank lines in the text file not being counted?

Question

I have created this function to return the number of lines in a text file:

int numberOfLinesInFile(string dataFile){            
    ifstream inputFile;
    inputFile.open("data.txt");
    int numberOfLines, data;

    while(!inputFile.eof()){
        inputFile >> data;
        numberOfLines++;
    }

    cout << "Number of lines: " << numberOfLines << endl;
    inputFile.close();
    return numberOfLines;
}

An interesting thing that I noticed is that the function counts the number of the non-blank lines (and an additional blank line at the end) correctly, but the additional blank lines are not being counted. For example, if this is my file:

234
453
657

then the function returns 4, since there are four lines in the text file. However, if my file contains more than one blank line at the end:

234
453
657

the function returns 4 again.

Why is this happening? Does this have to do with the eof instruction?

EDIT:

Okay, thank you @MikeCAT for making me understand where the problem was. Based on @MikeCAT's answer, I changed the while loop as:

while(!inputFile.eof()){
        if(inputFile >> data)
            numberOfLines++;
        else{
            cout << "Error while reading line " << numberOfLines + 1 << "!" << endl;
        }
}

I was incrementing numberOfLines without making sure that the line was actually read.

This doesn't address the question, but get in the habit of initializing objects with meaningful values rather than default-initializing them and immediately overwriting the default values. In this case, that means changing `ifstream inputFile; inputFile.open("data.txt");` to `ifstream inputFile("data.txt");`. And you don't need to call `inputFile.close();`. The destructor will do that. — Pete Becker, Sep 26 '20 at 12:41

score 2 · Accepted Answer · answered Sep 26 '20 at 04:52

Firstly, you are doing numberOfLines++; after inputFile >> data; without checking if the reading is successful. This is bad and lead to an extra counting.

Secondly, inputFile >> data; reads integer and skip whitespace characters before integers.

To avoid these problems, you should use std::getline() to count lines.

Also don't forget to initialize numberOfLines.

int numberOfLinesInFile(string dataFile){            
    ifstream inputFile;
    inputFile.open("data.txt");
    int numberOfLines = 0;
    std::string data;

    while(std::getline(inputFile, data)){
        numberOfLines++;
    }

    cout << "Number of lines: " << numberOfLines << endl;
    inputFile.close();
    return numberOfLines;
}

You could even take this a step further and use `std::cin.ignore()` instead of `cin::getline()` so that you are not wasting memory creating `std::string` values that are not used for anything. — Remy Lebeau, Sep 26 '20 at 09:09

(C++) Why are additional blank lines in the text file not being counted?

1 Answers1