Files and Stream

To handle large data, we use files on storage devices like floppy disks or hard disks for read and write operations. A file is a collection of related data stored on disk. The input/output system of C++ uses file streams as an interface between the programs and the files. 

Opening and closing a file 

The general format for opening a file is given as :  

              file-stream-class stream-object;  

              stream-object.open ("file name");    

Here, ifstream class is used to read a stream of objects from a file and ofstream class is used to write a stream of objects in a file . Function close () is used to close a file, which is opened for read, write or read and write operations. It is called automatically by destructor function. It can be called explicitly. 

 For example :            infile.close(); 

File pointers and their manipulations 

 Each file has two pointers. One is input pointer (get pointer) and other is output pointer (put pointer). We can use these pointers to move through the files while reading or writing. The input pointer is used for reading the contents of given file location and output pointer is used for writing to a given file location. To move file pointer to any other desired position, the file stream classes support the follwoing functions.  

1. seekg () Moves get pointer (input) to a specified location.
2. seekp () Moves put pointer (output) to a specified location.
3. tellg () Gives the current position of the get pointer. 
4. tellp () Gives the current position of the put pointer.