File Handling

Using C++ we can handle files present in the local drive of the system. This function of handling files using C++ is known as File Handling. We can open a file to read, write, append using fstream. When you open a file for reading or writing, it becomes stream. Stream is a sequence of bytes traveling from a source to a destination over a communication path.

Mode Flag Description
ios::out Open a file for writing
ios::app Append mode. All output to that file to be appended to the end
ios::in Open a file for reading
ios::ate Open a file for output and move the read/write control to the end of the file
ios::trunc If the file already exists, its contents will be truncated before opening the file

NOTE:
The major 3 mode Flags are out, app and in. Because they are used to write, append, and read a file.

CODE

EG 1 . Reading, Appending, Writing in a file using C++

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

int main() {
    fstream myFile;
    //----- 1. Writing -----
    myFile.open("CodersCapsule.txt",ios::out);
    myFile << "This is file handling" << endl;
    myFile.close();

    //----- 2. Appending -----
    myFile.open("CodersCapsule.txt",ios::app);
    myFile << "Iam appending this line" << endl;
    myFile.close();

    //----- 3. Reading -----
    myFile.open("CodersCapsule.txt", ios::in);
    string line;
    while (getline(myFile,line)) {
        cout << line << endl;
    }
}

OUTPUT
This is file handling
Iam appending this line

CODE EXPLANATION
In the above code, we included a header called fstream where files input, output can be done. Inside main method we created a new instance of fstream called myFile which we going to use to manipulate files. We seperated writing, appending and reading into 3 parts, will discuss about each.

1. Opening CodersCapsule.txt file using myFile.open() method, where we mentioned ios::out which means we are opening the file to write something inside it. So far we used cout to write sentance, same rule but instead of cout we are using myFile. Now in the local project folder a new notepad file called CodersCapsule will be created, compiler will open that file and write This is file handling text inside it. If we are using ios::out, whatever content already present inside CodersCapsule.txt file will be removed and newly given content will be written inside.

2. The function for appending content is same as that of writing, only difference is instead of ios::out we need to use ios::app. Here whatever content already present inside CodersCapsule.txt file will be kept and newly given content will be appended after it.

3. In order to read a file we need to give ios::in. Here we are opening CodersCapsule.txt file to read content present inside it. getline() is a method which is present inside string header. It is used to read value and store it to a variable. Here we used while loop in order to loop each and every lines. We are reading each and every line and storing it to a local variable called line and printing line value in console.


Exercises
1. Print 47th Multiplication table from 1 to 50 in a file.
2. Print Right angle triangle shape using * in a file.

(Click Here, For more exercises)