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NAMEfopen(), freopen(), fdopen() — open/reopen a stream file or convert file to stream SYNOPSIS#include <stdio.h> FILE *fopen(const char *__restrict pathname, const char *__restrict type); FILE *freopen(const char *__restrict pathname, const char *__restrict type, FILE *__restrict stream); FILE *fdopen(int fildes, const char *type); DESCRIPTION- fopen()
Opens the file named by
pathname
and associates a
stream
with it.
fopen()
returns a pointer to the
FILE
structure associated with the
stream. - freopen()
substitutes the named file in place of the open
stream.
The original
stream
is closed, regardless of whether the open ultimately succeeds.
freopen()
returns a pointer to the
FILE
structure associated with
stream
and makes an implicit call to
clearerr()
(see
ferror(3S)).
After a successful call to
freopen(),
the orientation of the
stream
is cleared (see
orientation(5)). freopen()
is typically used to attach the preopened
streams
associated with
stdin,
stdout,
and
stderr
to other files. - fdopen()
associates a stream with a file descriptor.
File descriptors are obtained from
open(),
dup(),
creat(),
or
pipe()
(see
open(2),
dup(2),
creat(2),
and
pipe(2)),
which open files but do not return pointers to a
FILE
structure stream.
Streams are necessary input for many of the Section (3S) library routines.
The
type
of stream must agree with the mode of the open file.
The meanings of
type
used in the
fdopen()
call are exactly as specified above, except that
w,
w+,
wb,
and
wb+
do not cause truncation of the file. - pathname
Points to a character string containing the name of the file to be opened. - type
Character string having one of the values listed below.
The
b
in the following values has no effect.
It exists to distinguish binary files from text files; however,
there is no distinction between these types of files on
UNIX systems (it is required for ISO C standard conformance).
- r or rb
open file for reading - w or wb
truncate to zero length or create file for writing - a or ab
append; open file for writing at end of file, or create file or writing - r+, rb+, or r+b
open file for update (reading and writing) - w+, wb+, or w+b
truncate file to zero length or create file for update - a+, ab+, or a+b
append; open or create file for update at end-of-file
When a file is opened for update,
both input and output can be done on the resulting
stream.
However, output cannot be directly followed by input
without an intervening call to
fflush()
or to a file positioning function
(fseek(),
fsetpos(),
or
rewind()),
and input cannot be directly followed by output
without an intervening call to a file positioning function
unless the input operation encounters end-of-file. When a file is opened for append (that is, when
type
is
a,
a+,
ab+,
or
a+b),
it is impossible to overwrite information already in the file.
All output is written at the end of the file,
regardless of intervening calls to
fseek().
If two separate processes open the same file for append,
each process can write freely to the file
without fear of destroying output being written by the other.
Output from the two processes will be intermixed in the file
in the order in which it is written. NotesHP-UX
binary file
types
are equivalent to their non-binary counterparts.
For example, types
r
and
rb
are equivalent. RETURN VALUEUpon successful completion,
fopen(),
fdopen()
and
freopen()
return a
FILE *
pointer to the stream.
Otherwise, a null pointer is returned and
errno
is set to indicate the error. ERRORSfopen(),
fdopen(),
and
freopen()
fail if:
- EBADF
The
fildes
argument is not a valid file descriptor. - EINVAL
The
type
argument is not a valid mode. - ENOMEM
There is insufficient space to allocate a buffer.
fopen()
and
freopen()
fail if:
- EACCES
Search permission is denied on a component of the path prefix,
or the file exists and the permissions specified by
type
are denied, or the file does not exist
and write permission is denied for the parent directory
of the file to be created. - EINTR
A signal was caught during
fopen()
or
freopen().
function. - EISDIR
The named file is a directory and
type
requires write access. - EMFILE
The calling process has attempted to exceed its open file limit. - ENAMETOOLONG
The length of the
pathname
string exceeds
PATH_MAX
or a pathname component is longer than
NAME_MAX
while
POSIX_NO_TRUNC
is in effect. - ENFILE
The system file table is full. - ENOENT
The named file does not exist or the
pathname
argument points to an empty string. - ENOSPC
The directory or file system that would contain the new file
cannot be expanded, the file does not exist, and it was to be created. - ENOTDIR
A component of the path prefix is not a directory. - ENXIO
The named file is a character special or block special file,
and the device associated with the special file does not exist. - EOVERFLOW
The named file is a regular file and the size of the file cannot
be represented correctly in an object of size
off_t
in this environment. - EROFS
The named file resides on a read-only file system and
type
requires write access.
Additional
errno
values can be set by the underlying
open()
call made from the
fopen()
and
freopen()
functions (see
open(2)). SEE ALSOcreat(2),
dup(2),
open(2),
pipe(2),
fclose(3S),
fgetpos64(3S),
fseek(3S),
popen(3S),
setbuf(3S),
orientation(5),
thread_safety(5),
glossary(9). STANDARDS CONFORMANCEfopen(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C fdopen(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1 freopen(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C |
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