C file input/output: Difference between revisions

Revision as of 09:03, 15 March 2006

Revision as of 19:31, 3 June 2006

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The '''mode''' parameter is a string that begins with one of the following sequences:

{| class="wikitable"

r Open a text file for reading

|-

w Truncate file to zero length or create text file for writing

!colspan=3| mode || description

a Append: open or create text file for writing at end-of-file

|-

rb Open a binary file for reading

|r || rb || || open for reading

wb Truncate file to zero length or create binary file for writing

|-

ab Append: open or create binary file for writing at end-of-file

|w || wb || || open for writing (file need not exist)

r+ Open text file for update (reading and writing)

|-

w+ Truncate file to zero length or create text file for update

|a+ || ab || Append:|| open orfor create textappending (file forneed update,not writing at end-of-fileexist)

|-

|r+b or|| rb+ Open|| binaryr+b file|| open for update (reading and writing), start at beginning

w+b or wb+ Truncate file to zero length or create binary file for update

|-

a+b or ab+ Append: open or create binary file for update, writing at end-of-file

|w+ || wb+ || w+b || open for reading and writing (overwrite file)

|-

|a+ || ab+ || a+b || open for reading and writing (append if file exists)

|}

The 'b' has no affect on the operation, but is included for clarity. It stands for binary. [http://www.opengroup.org/onlinepubs/009695399/functions/fopen.html]

The C standard gives two kinds of files — text files and binary files — although operating systems may or may not distinguish between the two. A ''text file'' is a file consisting of text arranged in lines with some sort of distinguishing end-of-line character or sequence (in [[Unix]], a bare linefeed character; in the [[Apple Macintosh|Macintosh]] OS, a bare carriage return; on [[DOS]] and [[Microsoft Windows]], a carriage return followed by a linefeed). When bytes are read in from a text file, an end-of-line sequence is usually mapped to a linefeed for ease in processing. When a text file is written to, a bare linefeed is mapped to the OS-specific end-of-line character sequence before writing. A ''binary file'' is a file where bytes are read in "raw," and delivered "raw," without any kind of mapping.

The C standard gives two kinds of files —- text files and binary files — although operating systems may or may not distinguish between the two. A ''text file'' is a file consisting of text arranged in lines with some sort of distinguishing end-of-line character or sequence (in [[Unix]], a bare linefeed character; in the [[Apple Macintosh|Macintosh]] OS, a bare carriage return; on [[DOS]] and [[Microsoft Windows]], a carriage return followed by a linefeed). When bytes are read in from a text file, an end-of-line sequence is usually mapped to a linefeed for ease in processing. When a text file is written to, a bare linefeed is mapped to the OS-specific end-of-line character sequence before writing. A ''binary file'' is a file where bytes are read in "raw," and delivered "raw," without any kind of mapping.

A convenient, but non-standard, way to find the length of a file in C is: