C++ code on how to read characters from a file

This tutorial will show you a small example of C++ code on how to read a characters from a file, as well as to count the number lines that any particular file consist of. We will be creating the script and compiling the C++ on a Linux system. All distros will work the same, provided you have the G++ compiler installed, which we will cover as well.

In this tutorial you will learn:

• How to install G++ on major Linux distros
• C++ code for reading lines of a file
• Compiling and running C++ program to read characters of file

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	G++ or other C++ compiler
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

Install G++ on major Linux distros

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In order to compile the C++ code that we present below, your system will have to have a C++ compiler installed. One of the best and most popular C++ compilers for Linux is G++. The GNU C++ Compiler is a compiler in Linux which was developed to compile C++ programs. The file extensions that can be compiled with G++ are .c and .cpp.

If you already have a different C++ compiler installed that you would prefer to use, that will work as well. Otherwise, use one of the following commands below to install the GNU C++ compiler with your Linux distribution’s package manager.

To install G++ on Ubuntu, Debian, and Linux Mint:

$ sudo apt install build-essential

To install G++ on CentOS, Fedora, AlmaLinux, and Red Hat:

$ sudo dnf install gcc-c++

To install G++ on Arch Linux and Manjaro:

$ sudo pacman -S gcc

Now that we have a compiler installed, move on to the section below to create the program.

C++ code to read characters from a file

Check out the C++ code below. The code will check for \n, the “new line character” and increase the number of lines stored in the number_of_lines integer variable. Every iteration will also print single character including \n to an output.

1. First, create a file called my-input-file.txt which will contain some text. For example:

   welcome to
   linuxconfig.org
   c++
   

2. Then, copy c++ code below to a file called read-characters.cpp:

   #include 
   #include 
   
   using namespace std;
   
   int main() {
   
   ifstream fin;
   fin.open("my-input-file.txt", ios::in);
   
   char my_character ;
   int number_of_lines = 0;
   
   	while (!fin.eof() ) {
   
   	fin.get(my_character);
   	cout << my_character;
   		if (my_character == '\n'){
   			++number_of_lines;
   		}
   	}
   cout << "NUMBER OF LINES: " << number_of_lines << endl;
   
   }
   

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3. Next, compile the code with the following command.

   $ g++ read-characters.cpp -o read-characters
   

4. Execute the newly compiled binary file.

   $ ./read-characters
   

   NOTE: your text file must be located in the same directory as your executable read-characters program. The while loop and fin.get will add an extra new line character so you may want to use the following line to start counting at -1 instead:

   int number_of_lines = -1
   

The output of the program in this example will be:

welcome to
linuxconfig.org
c++

NUMBER OF LINES: 4

Closing Thoughts

In this tutorial, we saw a C++ code snippet that can be used to count the number of lines in a text file. We also learned how to install the GNU C++ compiler on a variety of Linux distributions, so that our code can be compiled and run in a variety of environments.