fopen(3UCB) SunOS/BSD Compatibility Library Functions fopen(3UCB)NAME
fopen, freopen - open a stream
SYNOPSIS
/usr/ucb/cc [ flag ... ] file ...
#include <stdio.h>
FILE *fopen(file, mode)
const char *file, *mode;
FILE *freopen(file, mode, iop)
const char *file, *mode;
register FILE *iop;
DESCRIPTION
The fopen() function opens the file specified by file and associates a
stream with it. If the open succeeds, fopen() returns a pointer to be
used to identify the stream in subsequent operations. The file argument
points to a character string that contains the name of the file to be
opened. The mode argument is a character string having one of the fol‐
lowing 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
The freopen() function opens the file specified by file and associates
the stream pointed to by iop with it. The mode 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 iop.
The freopen() function is typically used to attach the preopened
streams associated withstdin, stdout, and stderr to other files.
When a file is opened for update, both input and output can be per‐
formed on the resulting stream. Output cannot be directly followed by
input without an intervening fseek(3C) or rewind(3C). Input cannot be
directly followed by output without an intervening fseek(3C) or
rewind(3C). An input operation that encounters EOF will fail.
RETURN VALUES
The fopen() and freopen() functions return a NULL pointer on failure.
USAGE
The fopen() and freopen() functions have transitional interfaces for
64-bit file offsets. See lf64(5).
SEE ALSOcc(1B), open(2), fclose(3C), fopen(3C), freopen(3C), fseek(3C), mal‐
loc(3C), rewind(3C), lf64(5)NOTES
Use of these functions should be restricted to applications written on
BSD platforms. Use of these functions with any of the system libraries
or in multithreaded applications is unsupported.
To support the same number of open files as the system, fopen() must
allocate additional memory for data structures using malloc(3C) after
64 files have been opened. This confuses some programs that use their
own memory allocators.
The fopen() and freopen() functions differ from the standard I/O func‐
tions fopen(3C) and freopen(3C). The standard I/O functions distinguish
binary from text files with an additional use of 'b' as part of the
mode, enabling portability of fopen(3C) and freopen(3C) beyond SunOS
4.x systems.
SunOS 5.10 30 Oct 2007 fopen(3UCB)