Introduction of file descriptor and read function

File Descriptor

  A file descriptor is an integer value used to identify and manage files or I/O devices in a computer system. File descriptors are employed when programs open, read, or write to files, and each descriptor uniquely represents a specific file or device. Typically, specific descriptor values like 0, 1, and 2 correspond to standard input, standard output, and standard error streams, while other descriptor values are allocated to files or devices opened or created by a program.