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fopen

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Revision as of 22:36, 31 May 2013 by P12bot (Talk | contribs)

 
 
File input/output


Functions
File access
fopenfopen_s
(C11)
(C95)
Direct input/output
Unformatted input/output
(C95)(C95)
(C95)
(C95)(C95)
(C95)
(C95)
Formatted input
Formatted output
File positioning
Error handling
Operations on files
 
Defined in header <stdio.h>
FILE *fopen( const char          *filename, const char          *mode );
(until C99)
FILE *fopen( const char *restrict filename, const char *restrict mode );
(since C99)

Opens a file indicated by filename and returns a file stream associated with that file. mode is used to determine the file access mode.

Parameters

filename - file name to associate the file stream to
mode - null-terminated character string determining file access mode
File access
mode string
Meaning Explanation Action if file
already exists
Action if file
does not exist
"r" read Open a file for reading read from start failure to open
"w" write Create a file for writing destroy contents create new
"a" append Append to a file write to end create new
"r+" read extended Open a file for read/write read from start error
"w+" write extended Create a file for read/write destroy contents create new
"a+" append extended Open a file for read/write write to end create new
File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has effect only on Windows systems.
On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.
File access mode flag "x" can optionally be appended to "w" or "w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it. (C11)
When using fopen_s or freopen_s, file access permissions for any file created with "w" or "a" prevents other users from accessing it. File access mode flag "u" can optionally be prepended to any specifier that begins with "w" or "a", to enable the default fopen permissions. (C11)

Return value

Opened file stream on success, NULL on failure

See also

closes a file
(function) [edit]
synchronizes an output stream with the actual file
(function) [edit]
open an existing stream with a different name
(function) [edit]