fopen(3S)               (BSD Compatibility Package)               fopen(3S)


   NAME
         fopen, freopen, fdopen - open a stream

   SYNOPSIS
         cc [ flag... ] file ... -lucb

         #include <stdio.h>

         FILE *fopen(filename, type)
         char *filename, *type;

         FILE *freopen(filename, type, stream)
         char *filename, *type;
         FILE *stream;

         FILE *fdopen(fildes, type)
         int fildes;
         char *type;

   DESCRIPTION
         fopen opens the file named by filename and associates a stream with
         it.  If the open succeeds, fopen returns a pointer to be used to
         identify the stream in subsequent operations.

         filename points to a character string that contains the name of the
         file to be opened.

         type is a character string having one of the following values:

               r    open for reading

               w    truncate or create for writing

               a    append: open for writing at end of file, or create for
                    writing

               r+   open for update (reading and writing)

               w+   truncate or create for update

               a+   append; open or create for update at EOF

         freopen opens the file named by filename and associates the stream
         pointed to by stream with it.  The type argument is used just as in
         fopen.  The original stream is closed, regardless of whether the open
         ultimately succeeds.  If the open succeeds, freopen returns the
         original value of stream.

         freopen is typically used to attach the preopened streams associated
         with stdin, stdout, and stderr to other files.



   7/91                                                                 Page 1

   fopen(3S)               (BSD Compatibility Package)               fopen(3S)


         fdopen associates a stream with the file descriptor fildes.  File
         descriptors are obtained from calls like open, dup, creat, or
         pipe(2), which open files but do not return streams.  Streams are
         necessary input for many of the Section 3S library routines.  The
         type of the stream must agree with the mode of the open file.

         When a file is opened for update, both input and output may be done
         on the resulting stream.  However, output may not be directly
         followed by input without an intervening fseek or rewind, and input
         may not be directly followed by output without an intervening fseek,
         rewind, or an input operation which encounters EOF.

   SEE ALSO
         open(2), pipe(2), fclose(3S), fseek(3S), fopen(3S), malloc(3C) in the
         Programmer's Reference Manual.

   RETURN VALUE
         fopen, freopen, and fdopen return a NULL pointer on failure.

   NOTES
         fopen differs from the library routine of the same name in the base
         system only in interface.

         In order to support the same number of open files that the system
         does, fopen must allocate additional memory for data structures using
         calloc [see malloc(3)] after 64 files have been opened.  This
         confuses some programs which use their own memory allocators.


























   Page 2                                                                 7/91