Files and Streams in C++

Modes for file opening

File modes will tell what is the purpose of opening a file i.e whether you need to read or write, or what operation you need to perform on that file, etc.

• ios::app: Append mode
• ios::ate: Open a file for output and read/write control to the end of the file
• ios::in: Open file for reading
• ios::out: Open file for writing
• ios::trunk: When any file already exists, its existing contents will be deleted before file opening

Opening and closing a file in C plus plus

Before working with file programs in C++  the programmer must have clarity about the following things

• A name to be given for the file
• Data type and structure of the file
• Purpose (reading, writing data)
• Opening method(file mode)
• Closing the file (after completing all operations)

Opening a file

• Before manipulating and performing operations on that file the general operation that is to be performed is opening that particular file
• A file is opened using a stream and any input and output operation performed in the stream will be also applied to the physical file that it is pointing to

In this program, the file that we are working with must be created in the directory and it is capable of performing both read and write operations

Example

#include <bits/stdc++.h>
using namespace std;
int main() 
{
  fstream file;
  file.open ("example.txt", ios::out | ios::in );
  return 0;
}

Closing a file

 C++ automatically terminates all the file resources and streams associated and  closes all open files when the program terminates but it’s always  a good programming practice to explicitly close the files

#include <bits/stdc++.h>
using namespace std;
int main() 
{
  ofstream file;
  file.open ("prepinsta.txt");
  file.close();
  return 0;
}

Mostly used functions for file handling in C plus plus

• open(): To create a file
• close(): To close an existing file
• get(): To read a single character from the file
• put(): To write a single character in the file
• read(): To read data from a file
• write(): To write data into a file

C++ program to demonstrate for reading from  and writing to a file

#include<bits/stdc++.h> 
using namespace std;

int  main()
{

  char text[200];

  fstream file;
  file.open ("prepinsta.txt", ios::out | ios::in );

  cout << "Write text to be written on file." << endl;
  cin.getline(text, sizeof(text));

  // Writing to file
  file << text << endl;

  // Reding from file
  file >> text;
  cout << text << endl;

  //closing the file
  file.close();
  return 0;
}