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freopen(3c)
Standard C Library Functions freopen(3C)
NAME
freopen - open a stream
freopen_s - open a stream with additional safety checks
SYNOPSIS
#include <stdio.h>
FILE *freopen(const char *filename, const char *mode, FILE *stream);
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
errno_t freopen_s(FILE *restrict *restrict newstreamptr,
const char *restrict filename, const char *restrict mode,
FILE *restrict stream);
DESCRIPTION
The freopen() function first attempts to flush the stream and close any
file descriptor associated with stream. Failure to flush or close the
file successfully is ignored. The error and end-of-file indicators for
the stream are cleared.
The freopen() function opens the file whose pathname is the string
pointed to by filename and associates the stream pointed to by stream
with it. The mode argument is used just as in fopen(3C).
If filename is a null pointer and the application conforms to SUSv3
(see standards(7)), the freopen() function attempts to change the mode
of the stream to that specified by mode, as though the name of the file
currently associated with the stream had been used. The following
changes of mode are permitted, depending upon the access mode of the
file descriptor underlying the stream:
o When is specified, the file descriptor mode must be O_RDWR.
o When r is specified, the file descriptor mode must be
O_RDONLY or O_RDWR.
o When a or w is specified, the file descriptor mode must be
O_WRONLY or O_RDWR.
If the filename is a null pointer and the application does not conform
to SUSv3, freopen() returns a null pointer.
The original stream is closed regardless of whether the subsequent open
succeeds.
After a successful call to the freopen() function, the orientation of
the stream is cleared, the encoding rule is cleared, and the associated
mbstate_t object is set to describe an initial conversion state.
The largest value that can be represented correctly in an object of
type off_t will be established as the offset maximum in the open file
description.
The freopen_s() function is part of the bounds checking interfaces
specified in the C11 standard, Annex K. It is similar to the freopen()
function with differing parameters and return type in order to provide
additional safety checks on the parameters passed before closing or
opening any files. See runtime_constraint_handler(3C) and
INCITS/ISO/IEC 9899:2011.
Implementation-defined features of freopen_s() include the following:
o If filename is a null pointer, the changes of mode permitted
are the same as those for the freopen() function.
o A runtime-constraint violation will be generated if either
newstreamptr, mode, or stream is a null pointer.
RETURN VALUES
Upon successful completion, freopen() returns the value of stream. Oth‐
erwise, a null pointer is returned and errno is set to indicate the
error.
If freopen_s() successfully opens filename, zero is returned. Otherwise
if freopen_s() did not open filename or there was a runtime-constraint
violation, a non-zero value is returned.
ERRORS
The freopen() and freopen_s() functions will fail if:
EACCES Search permission is denied on a component of the path
prefix, or the file exists and the permissions speci‐
fied by mode are denied, or the file does not exist and
write permission is denied for the parent directory of
the file to be created.
EBADF The application conforms to SUSv3, the filename argu‐
ment is a null pointer, and either the underlying file
descriptor is not valid or the mode specified when the
underlying file descriptor was opened does not support
the file access modes requested by the mode argument.
EFAULT The application does not conform to SUSv3 and the file‐
name argument is a null pointer.
EINTR A signal was caught during freopen().
EISDIR The named file is a directory and mode requires write
access.
ELOOP Too many symbolic links were encountered in resolving
filename.
EMFILE There are {OPEN_MAX} file descriptors currently open in
the calling process.
ENAMETOOLONG The length of the filename exceeds {PATH_MAX} or a
pathname component is longer than {NAME_MAX}.
ENFILE The maximum allowable number of files is currently open
in the system.
ENOENT A component of filename does not name an existing file
or filename is 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 this special file
does not exist.
EOVERFLOW The current value of the file position cannot be repre‐
sented correctly in an object of type off_t.
EROFS The named file resides on a read-only file system and
mode requires write access.
The freopen() function will fail if:
EINVAL The value of the mode argument is not valid.
ENAMETOOLONG Pathname resolution of a symbolic link produced an
intermediate result whose length exceeds {PATH_MAX}.
ENOMEM Insufficient storage space is available.
ENXIO A request was made of a non-existent device, or the
request was outside the capabilities of the device.
ETXTBSY The file is a pure procedure (shared text) file that is
being executed and mode requires write access.
The freopen_s() function will fail if:
EINVAL Null pointer is passed.
USAGE
The freopen() function is typically used to attach the preopened
streams associated with stdin, stdout and stderr to other files. By
default stderr is unbuffered, but the use of freopen() will cause it to
become buffered or line-buffered.
The freopen() function has a transitional interface for 64-bit file
offsets. For more information, see the lf64(7) man page.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSee below _
StandardSee standards(7).
The freopen() function can be used safely in multithreaded applica‐
tions.
The freopen_s() function cannot be used safely in a multithreaded
application due to the runtime constraint handler. For more informa‐
tion, see the runtime_constraint_handler(3C) man page.
SEE ALSO
fclose(3C), fdopen(3C), fopen(3C), fopen_s(3C), stdio(3C),
attributes(7), lf64(7), standards(7), runtime_constraint_handler(3C)
Oracle Solaris 11.4 17 Aug 2018 freopen(3C)