Synopsis

#include <stdio.h>

FILE *freopen(const char *restrict pathname, const char *restrict mode, FILE *restrict stream);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

Description

The purpose is to open the stream. The freopen() function shall first attempt to flush the stream associated with stream as if by a call to fflush(stream). Failure to flush the stream successfully shall be ignored. If pathname is not a null pointer, freopen() shall close any file descriptor associated with stream. Failure to close the file descriptor successfully shall be ignored. The error and end-of-file indicators for the stream shall be cleared.

The freopen() function shall open the file whose pathname is the string pointed to by pathname and associate the stream pointed to by stream with it. The mode argument shall be used just as in fopen().

The original stream shall be closed regardless of whether the subsequent open succeeds.

If pathname is a null pointer, the freopen() function shall attempt to change the mode of the stream to that specified by mode, as if the name of the file currently associated with the stream had been used. In this case, the file descriptor associated with the stream need not be closed if the call to freopen() succeeds. It is implementation-defined which changes of mode are permitted (if any), and under what circumstances.

After a successful call to the freopen() function, the orientation of the stream shall be cleared, the encoding rule shall be cleared, and the associated mbstate_t object shall be set to describe an initial conversion state. If pathname is not a null pointer, or if pathname is a null pointer and the specified mode change necessitates the file descriptor associated with the stream to be closed and reopened, the file descriptor associated with the reopened stream shall be allocated and opened as if by a call to open() with the following flags:

freopen() Mode open() Flags
r or rb O_RDONLY
w or wb O_WRONLY\|O_CREAT\|O_TRUNC
a or ab O_WRONLY\|O_CREAT\|O_APPEND
r+ or rb+ or r+b O_RDWR
w+ or wb+ or w+b O_RDWR\|O_CREAT\|O_TRUNC
a+ or ab+ or a+b O_RDWR\|O_CREAT\|O_APPEND

Return value

Upon successful completion, freopen() shall return the value of stream. Otherwise, a null pointer shall be returned, and errno shall be set to indicate the error.

Errors

The freopen() function shall fail if:

  • EACCES - Search permission is denied on a component of the path prefix, or the file exists and the permissions specified 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 file descriptor underlying the stream is not a valid file descriptor when pathname is a null pointer.

  • EINTR - A signal was caught during freopen().

  • EISDIR - The named file is a directory and mode requires write access.

  • ELOOP - A loop exists in symbolic links encountered during resolution of the path argument.

  • EMFILE - All file descriptors available to the process are currently open.

  • ENAMETOOLONG - The length of a component of a pathname is longer than NAME_MAX.

  • ENFILE - The maximum allowable number of files is currently open in the system.

  • ENOENT - The mode string begins with 'r' and a component of pathname does not name an existing file, or mode begins with 'w' or 'a' and a component of the path prefix of pathname does not name an existing file, or pathname is an empty string.

  • ENOENT or ENOTDIR - The pathname argument contains at least one non- character and ends with one or more trailing characters. If pathname without the trailing characters would name an existing file, an ENOENT error shall not occur.

  • 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 names an existing file that is neither a directory nor a symbolic link to a directory, or the pathname argument contains at least one non- character and ends with one or more trailing characters and the last pathname component names an existing file that is neither a directory nor a symbolic link to 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 named file is a regular file and the size of the file cannot be represented 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 may fail if:

  • EBADF - The mode with which the file descriptor underlying the stream was opened does not support the requested mode when pathname is a null pointer.

  • EINVAL - The value of the mode argument is not valid.

  • ELOOP - More than SYMLOOP_MAX symbolic links were encountered during resolution of the path argument.

  • ENAMETOOLONG - The length of a pathname exceeds PATH_MAX, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds PATH_MAX.

  • ENOMEM - Insufficient storage space is available.

  • ENXIO - A request was made of a nonexistent 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.

Tests

Untested

Known bugs

None

See Also

  1. Standard library functions
  2. Table of Contents