In computing, end-of-file (EOF)[1] is a condition in a computer operating system where no more data can be read from a data source. The data source is usually called a file or stream.
In the C standard library, the character reading functions such as getchar return a value equal to the symbolic value (macro) EOF to indicate that an end-of-file condition has occurred. The actual value of EOF is implementation-dependent and must be negative (but is commonly −1, such as in glibc[2]). Block-reading functions return the number of bytes read, and if this is fewer than asked for, then the end of file was reached or an error occurred (checking of errno or dedicated function, such as ferror is required to determine which).
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Input from a terminal never really "ends" (unless the device is disconnected), but it is useful to enter more than one "file" into a terminal, so a key sequence is reserved to indicate end of input. In UNIX the translation of the keystroke to EOF is performed by the terminal driver, so a program does not need to distinguish terminals from other input files. By default, the driver converts a Control-D character at the start of a line into an end-of-file indicator. To insert an actual Control-D (ASCII 04) character into the input stream, the user precedes it with a "quote" command character (usually Control-V). AmigaDOS is similar but uses Control-\ instead of Control-D.
In DOS and Windows (and in CP/M and many DEC operating systems such as the PDP-6 monitor,[3]RT-11, VMS or TOPS-10[4]), reading from the terminal will never produce an EOF. Instead, programs recognize that the source is a terminal (or other "character device") and interpret a given reserved character or sequence as an end-of-file indicator; most commonly this is an ASCIIControl-Z, code 26. Some MS-DOS programs, including parts of the Microsoft MS-DOS shell (COMMAND.COM) and operating-system utility programs (such as EDLIN), treat a Control-Z in a text file as marking the end of meaningful data, and/or append a Control-Z to the end when writing a text file. This was done for two reasons:
Backward compatibility with CP/M. The CP/M file system (and also the original 8-bit FAT implemented in Microsoft BASIC) only recorded the lengths of files in multiples of 128-byte "records", so by convention a Control-Z character was used to mark the end of meaningful data if it ended in the middle of a record. The FAT12 filesystem introduced with 86-DOS and MS-DOS has always recorded the exact byte-length of files, so this was never necessary on DOS.
It allows programs to use the same code to read input from both a terminal and a text file.
In the ANSI X3.27-1969 magnetic tape standard, the end of file was indicated by a tape mark, which consisted of a gap of approximately 3.5 inches of tape followed by a single byte containing the character 13 (hex) for nine-track tapes and 17 (octal) for seven-track tapes.[5] The end-of-tape, commonly abbreviated as EOT, was indicated by two tape marks. This was the standard used, for example, on IBM 360. The reflective strip that was used to announce impending physical end of tape was also called an EOT marker.
^"Table of IO Device Characteristics - Console or Teletypewriters". PDP-6 Multiprogramming System Manual(PDF). Maynard, Massachusetts, USA: Digital Equipment Corporation (DEC). 1965. p. 43. DEC-6-0-EX-SYS-UM-IP-PRE00. (PDF) from the original on 2014-07-14. Retrieved 2014-07-10. (1+84+10 pages)
^"5.1.1.1. Device Dependent Functions - Data Modes - Full-Duplex Software A(ASCII) and AL(ASCII Line)". PDP-10 Reference Handbook: Communicating with the Monitor - Time-Sharing Monitors(PDF). Vol. 3. Digital Equipment Corporation (DEC). 1969. pp. 5-3 – 5-6 [5-5 (431)]. (PDF) from the original on 2011-11-15. Retrieved 2014-07-10. (207 pages)
^"Tape Transfer (Pre-1977): Exchange Media: MARC 21 Specifications for Record Structure, Character Sets, and Exchange Media (Library of Congress)". www.loc.gov.
November 13, 2023
file, computing, file, condition, computer, operating, system, where, more, data, read, from, data, source, data, source, usually, called, file, stream, contents, details, character, also, referencesdetails, editin, standard, library, character, reading, funct. In computing end of file EOF 1 is a condition in a computer operating system where no more data can be read from a data source The data source is usually called a file or stream Contents 1 Details 2 EOF character 3 See also 4 ReferencesDetails editIn the C standard library the character reading functions such as getchar return a value equal to the symbolic value macro EOF to indicate that an end of file condition has occurred The actual value of EOF is implementation dependent and must be negative but is commonly 1 such as in glibc 2 Block reading functions return the number of bytes read and if this is fewer than asked for then the end of file was reached or an error occurred checking of a href Errno html class mw redirect title Errno errno a or dedicated function such as ferror is required to determine which EOF character editInput from a terminal never really ends unless the device is disconnected but it is useful to enter more than one file into a terminal so a key sequence is reserved to indicate end of input In UNIX the translation of the keystroke to EOF is performed by the terminal driver so a program does not need to distinguish terminals from other input files By default the driver converts a Control D character at the start of a line into an end of file indicator To insert an actual Control D ASCII 04 character into the input stream the user precedes it with a quote command character usually Control V AmigaDOS is similar but uses Control instead of Control D In DOS and Windows and in CP M and many DEC operating systems such as the PDP 6 monitor 3 RT 11 VMS or TOPS 10 4 reading from the terminal will never produce an EOF Instead programs recognize that the source is a terminal or other character device and interpret a given reserved character or sequence as an end of file indicator most commonly this is an ASCII Control Z code 26 Some MS DOS programs including parts of the Microsoft MS DOS shell COMMAND COM and operating system utility programs such as EDLIN treat a Control Z in a text file as marking the end of meaningful data and or append a Control Z to the end when writing a text file This was done for two reasons Backward compatibility with CP M The CP M file system and also the original 8 bit FAT implemented in Microsoft BASIC only recorded the lengths of files in multiples of 128 byte records so by convention a Control Z character was used to mark the end of meaningful data if it ended in the middle of a record The FAT12 filesystem introduced with 86 DOS and MS DOS has always recorded the exact byte length of files so this was never necessary on DOS It allows programs to use the same code to read input from both a terminal and a text file In the ANSI X3 27 1969 magnetic tape standard the end of file was indicated by a tape mark which consisted of a gap of approximately 3 5 inches of tape followed by a single byte containing the character 13 hex for nine track tapes and 17 octal for seven track tapes 5 The end of tape commonly abbreviated as EOT was indicated by two tape marks This was the standard used for example on IBM 360 The reflective strip that was used to announce impending physical end of tape was also called an EOT marker See also editEnd of Transmission character EOT Substitute character End of message Here document 30 References edit Pollock Wayne Shell Here Document Overview hccfl edu Archived from the original on 2014 05 29 Retrieved 2014 05 28 The GNU C Library www gnu org Table of IO Device Characteristics Console or Teletypewriters PDP 6 Multiprogramming System Manual PDF Maynard Massachusetts USA Digital Equipment Corporation DEC 1965 p 43 DEC 6 0 EX SYS UM IP PRE00 Archived PDF from the original on 2014 07 14 Retrieved 2014 07 10 1 84 10 pages 5 1 1 1 Device Dependent Functions Data Modes Full Duplex Software A ASCII and AL ASCII Line PDP 10 Reference Handbook Communicating with the Monitor Time Sharing Monitors PDF Vol 3 Digital Equipment Corporation DEC 1969 pp 5 3 5 6 5 5 431 Archived PDF from the original on 2011 11 15 Retrieved 2014 07 10 207 pages Tape Transfer Pre 1977 Exchange Media MARC 21 Specifications for Record Structure Character Sets and Exchange Media Library of Congress www loc gov Retrieved from https en wikipedia org w index php title End of file amp oldid 1147557601, wikipedia, wiki, book, books, library,
