• In my previous post titled “What is File?” I explained about the concept of file, file attributes and file types. This post is the supplementary for the same so if you haven’t read that post yet, I strongly recommend to read that first before proceeding to this one. This post deals with the basic operations performed on the file.
  • A file is an abstract data type. To define a file properly, we need to consider the operation performed on the file.
  • Operating System can provide system calls to create, write, read, reposition, delete and truncate files.

Creating a File

  • Creation of a file is the first operation. For creating a file two steps are necessary.
  1. Required space must be allocated.
  2. An entry for new file must be made in the directory.
  • The directory entry records the name of the file and the location in the file system.

Writing a File

  • For file writing operation, we make a system call specifying both the name of a file and the information to be written into the file.
  • System searches the entire directory structure to find the location of the specified file.
  • System keeps a write pointer that keeps track of writing at the location in the file.
  • The system updates write pointer each time whenever a file write operation occurs.

Reading a File

  • To perform file read operation, we use a system call that specifies name of the file and the block of the file to read from it.
  • Again the directory is searched for the specified file.
  • System keeps a read pointer that keeps track of reading location in the file.
  • The system updates read pointer each time whenever a file read operation occurs

Repositioning Within a File

  • Repositioning within a file operation does not involve any actual input output.
  • The directory is searched for the appropriate entry and the current file position is set to a given value.
  • It is also known as files seek operation.

Deleting a File

  • File deletion operation also requires searching of a specified file entry within the directory structure.
  • As soon as the file is deleted, space allocated to that file becomes available for further use.

Truncating a File

  • In some cases the user may want to erase the file contents but keep its attributes as it is. This operation is called truncating a file.
  • Instead of delete a file and recreating it with same attributes, this function allows all attributes to remain unchanged except the file content.
  • File length attribute is reset to a length zero and its file space is released.

Leave a Reply

Your email address will not be published. Required fields are marked *