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Top Forums Programming difference between fdopen() and freopen() Post 32604 by Perderabo on Monday 2nd of December 2002 11:02:24 AM
Old 12-02-2002
freopen is the same thing as an fclose followed by an fopen. You might use it if you had a list of list to loop through. To go the the next file, you would just freopen() it. That would close the current file and open the new file. It's ok to use freopen() even on the first file.

fdopen takes a file opened by a system call and wraps a FILE structure around it. The file stays opened, but now it looks like fopen() opened it. So now all of the standard c library stuff like fprintf() can be used on it.

You should be able to type "man fdopen" and "man freopen" to get man pages on these functions.
 

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FOPEN(3S)																 FOPEN(3S)

NAME
fopen, freopen, fdopen - open a stream SYNOPSIS
#include <stdio.h> FILE *fopen(filename, type) char *filename, *type; FILE *freopen(filename, type, stream) char *filename, *type; FILE *stream; FILE *fdopen(fildes, type) char *type; DESCRIPTION
Fopen opens the file named by filename and associates a stream with it. Fopen returns a pointer to be used to identify the stream in sub- sequent operations. Type 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 Freopen substitutes the named file in place of the open stream. It returns the original value of stream. The original stream is closed. Freopen is typically used to attach the preopened constant names, stdin, stdout, stderr, to specified files. Fdopen associates a stream with a file descriptor obtained from open, dup, creat, or pipe(2). The type of the stream must agree with the mode of the open file. SEE ALSO
open(2), fclose(3) DIAGNOSTICS
Fopen and freopen return the pointer NULL if filename cannot be accessed. BUGS
Fdopen is not portable to systems other than UNIX. FOPEN(3S)
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