RE: When is a file open but not open?
RE: When is a file open but not open?
- Subject: RE: When is a file open but not open?
- From: Emmanuel <email@hidden>
- Date: Fri, 5 Aug 2005 19:42:03 +0200
At 12:08 PM -0400 8/5/05, Grimm, Kenneth wrote:
So when would I use just "write" in place of the "open for
access/write/close for access" dance?
Note that when you just "write" you write to the beginning of the
file, but you do not shorten the file: if you write "R" to a file
which stores "Bush" you get "Rush".
Is one safer? Provides file locking? All my books suggest the dance, not
just the "write"... can you explain further why one and not the other, or do
both have their place in certain instances?
There are two instances that I know where you want to open the file
with write permission before writing.
1 - you need sequential access: for instance, you want to write
several things one after the other:
write "hello"
write " "
write "world"
If you do that the file being not open, as I told above you write and
rewrite the beginning of the file only.
2 - you need to be sure that no-one is also writing to the file: open
with write permission does lock the file - actually I think it's the
OS' genuine mechanism to lock whatever resource might be accessed by
several clients.
Emmanuel
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