fopen(3) [minix man page]
FOPEN(3) Library Functions Manual FOPEN(3) NAME
fopen, freopen, fdopen - open a stream SYNOPSIS
#include <stdio.h> FILE *fopen(const char *filename, const char *type) FILE *freopen(const char *filename, const char *type, FILE *stream) FILE *fdopen(int fildes, const char *type) DESCRIPTION
Fopen opens the file named by filename and associates a stream with it. Fopen returns a pointer to be used to identify the stream in sub- sequent operations. Type is a character string having one of the following values: "r" open for reading "w" create for writing "a" append: open for writing at end of file, or create for writing In addition, each type may be followed by a "+" to have the file opened for reading and writing. "r+" positions the stream at the begin- ning of the file, "w+" creates or truncates it, and "a+" positions it at the end. Both reads and writes may be used on read/write streams, with the limitation that an fseek, rewind, or reading an end-of-file must be used between a read and a write or vice-versa. Freopen substitutes the named file in place of the open stream. It returns the original value of stream. The original stream is closed. Freopen is typically used to attach the preopened constant names, stdin, stdout, stderr, to specified files. Fdopen associates a stream with a file descriptor obtained from open, dup, creat, or pipe(2). The type of the stream must agree with the mode of the open file. SEE ALSO
open(2), fclose(3). DIAGNOSTICS
Fopen and freopen return the pointer NULL if filename cannot be accessed, if too many files are already open, or if other resources needed cannot be allocated. BUGS
Fdopen is not portable to systems other than UNIX. The read/write types do not exist on all systems. Those systems without read/write modes will probably treat the type as if the "+" was not present. These are unreliable in any event. 4th Berkeley Distribution May 27, 1986 FOPEN(3)
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FOPEN(3) Linux Programmer's Manual FOPEN(3) NAME
fopen, fdopen, freopen - stream open functions 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 appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file. a+ Open for reading and appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file. The mode string can also include the letter ``b'' either as a last character or as a character between the characters in any of the two- character strings described above. This is strictly for compatibility with ANSI X3.159-1989 (``ANSI C'') and has no effect; the ``b'' is ignored on all POSIX conforming systems, including Linux. (Other systems may treat text files and binary files differently, and adding the ``b'' may be a good idea if you do I/O to a binary file and expect that your program may be ported to non-Unix environments.) 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. Note that ANSI C requires that a file positioning function inter- vene between output and input, unless an input operation encounters end-of-file. (If this condition is not met, then a read is allowed to return the result of writes other than the most recent.) Therefore it is good practice (and indeed sometimes necessary under Linux) to put an fseek or fgetpos operation between write and read operations on such a stream. This operation may be an apparent no-op (as in fseek(..., 0L, SEEK_CUR) called for its synchronizing side effect. Opening a file in append mode (a as the first character of mode) causes all subsequent write operations to this stream to occur at end-of- file, as if preceded by an fseek(stream,0,SEEK_END); call. The fdopen function associates a stream with the existing file descriptor, fildes. The mode of the stream (one of the values "r", "r+", "w", "w+", "a", "a+") must be compatible with the mode of the file descriptor. The file position indicator of the new stream is set to that belonging to fildes, and the error and end-of-file indicators are cleared. Modes "w" or "w+" do not cause truncation of the file. The file descriptor is not dup'ed, and will be closed when the stream created by fdopen is closed. The result of applying fdopen to a shared memory object is undefined. 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 VALUE
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). CONFORMING TO
The fopen and freopen functions conform to ANSI X3.159-1989 (``ANSI C''). The fdopen function conforms to IEEE Std1003.1-1988 (``POSIX.1''). SEE ALSO
open(2), fclose(3), fileno(3) BSD MANPAGE
2002-01-03 FOPEN(3)