FreeBSD 7.0 manual page repository

FreeBSD is a free computer operating system based on BSD UNIX originally. Many IT companies, like DeployIS is using it to provide an up-to-date, stable operating system.

fopen, fdopen, freopen - stream open functions

 

NAME

      fopen, fdopen, freopen - stream open functions
 

LIBRARY

      Standard C Library (libc, -lc)
 

SYNOPSIS

      #include <stdio.h>
 
      FILE *
      fopen(const char * restrict path, const char * restrict 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 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.
 
      If the path argument is NULL, freopen() attempts to re-open the file
      associated with stream with a new mode.  The new mode must be compatible
      with the mode that the stream was originally opened with:
 
                  Streams originally opened with mode “r” can only be reopened
                with that same mode.
 
                  Streams originally opened with mode “a” can be reopened with
                the same mode, or mode “w”.
 
                  Streams originally opened with mode “w” can be reopened with
                the same mode, or mode “a”.
 
                  Streams originally opened with mode “r+”, “w+”, or “a+” can be
                reopened with any mode.
 
      The primary use of the freopen() function is to change the file associ‐
      ated with a standard text stream (stderr, stdin, or stdout).
      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 argument 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).
      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”).
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.