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FreeBSD man pages : fopen (3)
FOPEN(3)	       FreeBSD Library Functions Manual 	      FOPEN(3)

NAME

fopen, fdopen, freopen - stream open functions

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdio.h> FILE * fopen(const char *path, const char *mode); FILE * fdopen(int fildes, const char *mode); FILE * freopen(const char *path, const char *mode, FILE *stream);

DESCRIPTION

The fopen() function opens the file whose name is the string pointed to by path and associates a stream with it. The argument mode points to a string beginning with one of the following sequences (Additional characters may follow these sequences.): ``r'' Open text file for reading. The stream is positioned at the beginning of the file. ``r+'' Open for reading and writing. The stream is positioned at the beginning of the file. ``w'' Truncate file to zero length or create text file for writing. The stream is positioned at the beginning of the file. ``w+'' Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file. ``a'' Open for writing. The file is created if it does not exist. The stream is positioned at the end of the file. Subsequent writes to the file will always end up at the then current end of file, irrespective of any intervening fseek(3) or similar. ``a+'' Open for reading and writing. The file is created if it does not exist. The stream is positioned at the end of the file. Subse- quent writes to the file will always end up at the then current end of file, irrespective of any intervening fseek(3) or similar. The mode string can also include the letter ``b'' either as a third char- acter or as a character between the characters in any of the two-charac- ter strings described above. This is strictly for compatibility with ISO/IEC 9899:1990 (``ISO C89'') and has no effect; the ``b'' is ignored. Any created files will have mode "S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH" (0666), as modified by the process' umask value (see umask(2)). Reads and writes may be intermixed on read/write streams in any order, and do not require an intermediate seek as in previous versions of stdio. This is not portable to other systems, however; ANSI C requires that a file positioning function intervene between output and input, unless an input operation encounters end-of-file. The fdopen() function associates a stream with the existing file descrip- tor, fildes. The mode of the stream must be compatible with the mode of the file descriptor. When the stream is closed via fclose(3), fildes is closed also. The freopen() function opens the file whose name is the string pointed to by path and associates the stream pointed to by stream with it. The original stream (if it exists) is closed. The mode argument is used just as in the fopen() function. The primary use of the freopen() function is to change the file associated with a standard text stream (stderr, stdin, or stdout).

RETURN VALUES

Upon successful completion fopen(), fdopen() and freopen() return a FILE pointer. Otherwise, NULL is returned and the global variable errno is set to indicate the error.

ERRORS

[EINVAL] The mode provided to fopen(), fdopen(), or freopen() was invalid. The fopen(), fdopen() and freopen() functions may also fail and set errno for any of the errors specified for the routine malloc(3). The fopen() function may also fail and set errno for any of the errors specified for the routine open(2). The fdopen() function may also fail and set errno for any of the errors specified for the routine fcntl(2). The freopen() function may also fail and set errno for any of the errors specified for the routines open(2), fclose(3) and fflush(3).

SEE ALSO

open(2), fclose(3), fileno(3), fseek(3), funopen(3)

STANDARDS

The fopen() and freopen() functions conform to ISO/IEC 9899:1990 (``ISO C89''). The fdopen() function conforms to IEEE Std 1003.1-1988 (``POSIX.1''). FreeBSD 4.8 June 4, 1993 FreeBSD 4.8