r+ and w+

[Unregistered]

What is the difference between these two modes of writing to a file?

[Prelude]

r+ simply opens the file for both reading and writing.
w+ opens the file for reading and writing, but discards the contents of the file or creates the file if it doesn't exist.

-Prelude

[Unregistered]

Thanks, Prelude. Hope I didn't offend you on Saturday. You sure know your stuff!

[stautze]

In K&R w and w+ have the same description except for on word. w writes and w+ updates. What is the difference?

[Prelude]

>Hope I didn't offend you on Saturday
About what?

>In K&R w and w+ have the same description except for on word.
>w writes and w+ updates. What is the difference?

K&R pp.242

FILE *fopen(const char *filename, const char *mode)
fopen opens the named file, and returns a stream or NULL if the attempt fails.
Legal values for mode include

"r" open text file for reading
"w" create text file for writing; discard previous contents if any
"a" append; open or create text file for writing at end of file
"r+" open text file for update (i.e., reading and writing)
"w+" create text file for update; discard previous contents of any
"a+" append; open or create text file for update, writing at end

Update mode permits reading and writing the same file; fflush or a file-positioning function must be called between a read and a write or vice versa. If the mode includes b after the initial letter, as in "rb" or "w+b", that indicates a binary file. Filenames are limited to FILENAME_MAX characters. At most FOPEN_MAX files may be open at once.

-Prelude

[stautze]

Thanks, I should have read further.