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.
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  Sec-
tion 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.