Computer Systems: A Programmer's Perspective (3rd Edition)
Computer Systems: A Programmer's Perspective (3rd Edition)
3rd Edition
ISBN: 9780134092669
Author: Bryant, Randal E. Bryant, David R. O'Hallaron, David R., Randal E.; O'Hallaron, Bryant/O'hallaron
Publisher: PEARSON
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Chapter 10.3, Problem 10.1PP
Program Plan Intro

Opening and Closing files:

Using “Open” function, a process can open an existing file or generates a new file.

  • This function is used to converts a filename to a file descriptor and returns the result as a descriptor number.
  • The descriptor returned is always the lowest descriptor that is not presently open in the process.
  • Each process in the LINUX begins life with three open files.
    • Descriptor 0 – standard input.
    • Descriptor 1 – standard output.
    • Descriptor 2 – standard error.
  • The “open” function consists of three arguments. That is “Open(filename, flags, mode)”.
    • The argument “filename” defines the name of the given file.
    • The argument “flags” represents how the process plans to access the file. Some flags names are as follows.
      • O_RDONLY – it means reading only.
      • O_WRONLY – it means writing only.
      • O_RDWR – it means reading and writing.
    • The “mode” argument identifies the access permission bits of new files.

Example:

The example for open an existing file for reading is shown below:

sample1 = Open("foo1.txt", O_RDONLY, 0);

From the above “open” function,

  • The filename is “foo1.txt”.
  • Flag name is “O_RDONLY”.
  • Mode is “0”.

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