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”.