Difference between revisions of "c/io/fopen"

Revision as of 19:17, 22 March 2013

Defined in header `<stdio.h>`
FILE fopen( const char filename, const char *mode );

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

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	return NULL and set error
"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	return NULL and set 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 no effect on POSIX systems, but on Windows, for example, it disables special handling of '\n' and '\x1A'. 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. (C++17)
The behavior is undefined if the mode is not one of the strings listed above. Some implementations define additional supported modes (e.g. Windows).

Opened file stream on success, NULL on failure

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 {{param list item | mode | null-terminated character string determining file access mode
-{{cpp/io/c/file access flags}}}}
+{{cpp/io/c/file access flags|c}}}}
 {{param list end}}