C++ Files and Streams

C++ Files and Streams

In C++ programming we are using the iostream standard library, it provides cin and cout methods for reading from input and writing to output respectively.

To read and write from a file we are using the standard C++ library called fstream. Let us see the data types define in fstream library is:

Data Type Description
fstream It is used to create files, write information to files, and read information from files.
ifstream It is used to read information from files.
ofstream It is used to create files and write information to the files.

User-defined exception example

Let's see the simple example of user-defined exception in which std::exception class is used to define the exception.

FileStream example: writing to a file:

Let's see the simple example of writing to a text file testout.txt using C++ FileStream programming.

    #include <iostream>  
    #include <fstream>  
    using namespace std;  
    int main () {  
      ofstream filestream("testout.txt");  
      if (filestream.is_open())  
      {  
        filestream << "Welcome to javaTpoint.\n";  
        filestream << "C++ Tutorial.\n";  
        filestream.close();  
      }  
      else cout <<"File opening is fail.";  
      return 0;  
    }  

Output:

The content of a text file testout.txt is set with the data:
Welcome to javaTpoint.
C++ Tutorial.

FileStream example: reading from a file

Let's see the simple example of reading from a text file testout.txt using C++ FileStream programming.

    #include <iostream>  
    #include <fstream>  
    using namespace std;  
    int main () {  
      string srg;  
      ifstream filestream("testout.txt");  
      if (filestream.is_open())  
      {  
        while ( getline (filestream,srg) )  
        {  
          cout << srg <<endl;  
        }  
        filestream.close();  
      }  
      else {  
          cout << "File opening is fail."<<endl;   
        }  
      return 0;  
    }  

Note: Before running the code a text file named as "testout.txt" is need to be created and the content of a text file is given below:

Welcome to javaTpoint.

C++ Tutorial.

Output:

Welcome to javaTpoint.
C++ Tutorial.

C++ Read and Write Example

Let's see the simple example of writing the data to a text file testout.txt and then reading the data from the file using C++ FileStream programming.

    #include <fstream>  
    #include <iostream>  
    using namespace std;  
    int main () {  
       char input[75];  
       ofstream os;  
       os.open("testout.txt");  
       cout <<"Writing to a text file:" << endl;  
       cout << "Please Enter your name: ";   
       cin.getline(input, 100);  
       os << input << endl;  
       cout << "Please Enter your age: ";   
       cin >> input;  
       cin.ignore();  
       os << input << endl;  
       os.close();  
       ifstream is;   
       string line;  
       is.open("testout.txt");   
       cout << "Reading from a text file:" << endl;   
       while (getline (is,line))  
       {  
       cout << line << endl;  
       }      
       is.close();  
       return 0;  
    }  

Output:

Writing to a text file:
Please Enter your name: Nakul Jain
Please Enter your age: 22
Reading from a text file: Nakul Jain
22