| FOPEN(3) | Library Functions Manual | FOPEN(3) | 
fopen, fdopen,
  freopen —
#include <stdio.h>
FILE *
  
  fopen(const
    char * restrict path,
    const char * restrict
    mode);
FILE *
  
  fdopen(int
    fildes, const char
    *mode);
FILE *
  
  freopen(const
    char * restrict path,
    const char * restrict
    mode, FILE * restrict
    stream);
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, which may be followed by additional modifiers as indicated below:
a”a+”r”r+”w”w+”After one of those, the mode string can also include one or more of the following modifier letters:
O_CLOEXEC) flag of the file descriptor, which
      means that it will not be available after an
      exec(3) system call. This is a
      non ANSI X3.159-1989
      (“ANSI C89”) extension.fopen() to regular files; if the file opened is
      not a regular file, fopen() will close it, and
      fail. This is a non ANSI X3.159-1989
      (“ANSI C89”) extension.O_NOFOLLOW) flag of the
      file descriptor, which means that if the last path component is a symbolic
      link, it will not be followed. This is a non ANSI
      X3.159-1989 (“ANSI C89”) extension.O_EXCL) which means that the file will
      not be created if it already exists. In that case
      fopen() will fail.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(2) value.
Opening a file with append mode causes all subsequent writes to it to be forced to the then current end of file, regardless of intervening repositioning of the stream.
The fopen() and
    freopen() functions initially position the stream at
    the start of the file unless the file is opened with append mode, in which
    case the stream is initially positioned at the end of the file.
The fdopen() function associates a stream
    with the existing file descriptor, fildes. The
    mode of the stream must be compatible with the mode of
    the file descriptor. The stream is positioned at the file offset of the file
    descriptor.
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).
Input and output against the opened stream will be fully buffered, unless it refers to an interactive terminal device, or a different kind of buffering is specified in the environment. See setvbuf(3) for additional details.
fopen(),
  fdopen() and freopen() return
  a FILE pointer. Otherwise, NULL is returned and the
  global variable errno is set to indicate the error.
EFTYPE]EINVAL]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).
fopen() and freopen()
  functions conform to ANSI X3.159-1989
  (“ANSI C89”). All three functions are specified in
  IEEE Std 1003.1-2008 (“POSIX.1”).
fopen() function appeared in
  Version 1 AT&T UNIX.
fdopen() with error checking should
  close(2)
  fildes in case of failure, and
  fclose(3) the resulting FILE *
  in case of success.
	FILE *file;
	int fd;
	if ((file = fdopen(fd, "r")) != NULL) {
		/* perform operations on the FILE * */
		fclose(file);
	} else {
		/* failure, report the error */
		close(fd);
	}
| September 2, 2019 | NetBSD 10.0 |