FOPEN(3S)           UNIX Programmer's Manual            FOPEN(3S)

NAME
     fopen, freopen, fdopen - open or re-open a stream file; con-
     vert file to stream

SYNOPSIS
     #include <stdio.h>

     FILE *fopen (file-name, type)
     char *file-name, *type;

     FILE *freopen (file-name, type, stream)
     char *file-name, *type;
     FILE *stream;

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

HP-UX COMPATIBILITY
     Level:    HP-UX/RUN ONLY

     Origin:   System V

DESCRIPTION
     _F_o_p_e_n opens the file named by  _f_i_l_e-_n_a_m_e  and  associates  a
     stream with it.  _F_o_p_e_n returns a pointer to be used to iden-
     tify the stream in subsequent operations.

     _T_y_p_e 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

          r+      open for update (reading and writing)

          w+      create for update

          a+      append; open or create for  update  at  end  of
                  file

     _F_r_e_o_p_e_n substitutes the named file  in  place  of  the  open
     _s_t_r_e_a_m.   It returns the original value of _s_t_r_e_a_m.  The ori-
     ginal stream is closed, regardless of whether the open ulti-
     mately succeeds.

     _F_r_e_o_p_e_n is typically used to attach the  preopened  constant
     names stdin, stdout, and stderr to specified files.

     _F_d_o_p_e_n associates a stream with a file  descriptor  obtained
     from  _o_p_e_n,  _d_u_p, _c_r_e_a_t, or _p_i_p_e(2).  The _t_y_p_e 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  _f_s_e_e_k  or
     _r_e_w_i_n_d,  and  input  may  not be directly followed by output
     without an intervening _f_s_e_e_k, _r_e_w_i_n_d, or an input  operation
     which encounters end of file.

     When a file is opened for append (i. e., when /fItype  is  a
     or a+), it is impossible to overwrite information already in
     the file. _F_s_e_e_k may be used to reposition the  file  pointer
     to  any  position in the file, but when output is written to
     the file, the current file pointer is disregarded.  All out-
     put  is  written  at the end of the file and causes the file
     pointer to be repositioned at the end of the output.  If two
     separate  processes open the same file for append, each pro-
     cess may write freely to the file without fear of destroying
     output  being written by the other.  The output from the two
     processes will be intermixed in the file in the order  which
     it is written.

SEE ALSO
     creat(2), dup(2), open(2), pipe(2),  fclose(3S),  fseek(3s),
     popen(3S).

DIAGNOSTICS
     _F_o_p_e_n and _f_r_e_o_p_e_n return the pointer NULL if _f_i_l_e-_n_a_m_e  can-
     not be accessed, if there are too many open files, or if the
     arguments are incorrect.

     _F_d_o_p_e_n returns a NULL if there are too many open  files,  or
     if the arguments are ill-formed.