How to Count the Number of Lines in a File in C++

In this article, we show how to count the number of lines in a file in C++.

Sometimes, you may be working with a file and you want to know how large is the file, in terms of the number of lines.

Even though C++ doesn't have a direct function that obtains the number of lines, we can do so fairly easily with a bit of code.

So in this code, we will take a simple text file and find how many lines it contains.

This is shown in the code below.

#include <fstream> #include <iostream> #include <string> using namespace std; int main() { string line; int numlines= 0; ifstream reader("file1.txt"); if (!reader) { cout << "There was an error opening file" << endl; return -1; } while (!reader.eof()) { getline(reader, line); numlines++; } reader.close(); cout << "The number of lines in this file is " << numlines << endl; return 0; }

We use the library to work with files. In this case, we are opening up a file and reading the contents of it, specifically the number of lines.

We use the library to output the number of lines in the file.

We use the library because we're going to read in the lines through a string variable.

So we go to the main function.

Within this main function, the first thing we do is create a string, line.

We then create our connection to the file we want to read from, which in this case is "file1.txt". We do this by creating an ifstream reader object and then passing in the filename as its parameter. You create an ofstream writer object if you want to write to a file. You create an ifstream reader object if you want to read from a file.

We then output an error message if there is a problem opening the file.

We then create a while loop.

The point of the while loop is that while there are still lines left in the file, we want to go through each of them. Therefore, during each line iteration, we are able to increase the count of the variable, numLines. This way, we are able to keep track of all of the lines. When C++ reads the contents of a file, it doesn't read the whole thing as one. It reads the file line by line until it reaches the last line. In fact, the eof() function which we use in this code stands for end of file. We create a while loop that goes until the reader reaches the end of file, and then it stops. Thus, we know that with this counter, we have counted all the lines all the way to the end of the file.

When C++ reaches the end of file, the while loop terminates; thus, no more lines are read by the program.

We then close the reader object, as reading of the file is now finished.

So this is an effective and easy way to count the number of lines in a file in C++.

And this is how to read the contents of a file in C++.

Related Resources

How to Write Contents to a File in C++

How to Append Contents to a File in C++