Why Is Escaping Data Considered So Magical?

[Cameron Simpson]

On 29Jun2010 21:49, Carl Banks <pavlovevidence at gmail.com> wrote:
| On Jun 28, 2:44 am, Gregory Ewing <greg.ew... at canterbury.ac.nz> wrote:
| > Carl Banks wrote:
| > > Indeed, strncpy does not copy that final NUL if it's at or beyond the
| > > nth element.  Probably the most mind-bogglingly stupid thing about the
| > > standard C library, which has lots of mind-boggling stupidity.
| >
| > I don't think it was as stupid as that back when C was
| > designed. Every byte of memory was precious in those days,
| > and if you had, say, 10 bytes allocated for a string, you
| > wanted to be able to use all 10 of them for useful data.
| >
| > So the convention was that a NUL byte was used to mark
| > the end of the string *if it didn't fill all the available
| > space*.
| 
| I can't think of any function in the standard library that observes
| that convention, which inclines me to disbelieve this convention ever
| really existed.  If it did, there would be functions to support it.
| 
| For that matter, I'm not really inclined to believe bytes were *that*
| precious in those days.

Jeez. PDP-11s, 16 bit addressing, tiny tiny disc drives!

The original V7 (and probably earlier) UNIX filesystem has 16 byte directory
entries: 2 bytes for an inode and 14 bytes for the name. You could use 14
bytes of that name, and strncpy makes it effective to work with that data
structure.  

Shortening something already only 14 bytes (the name) _is_ a big ask,
and it is well work the unusual convention in play.

| The obvious rationale behind strncpy's stupid behavior is that it's
| not a string function at all, but a memory block function, that stops
| at a NUL in case you don't care what's after the NUL in a block.  But
| it leads you to believe it's a string function by it's name.

Bah. It's for copying a _string_ into a _buffer_! Strangely, since it
starts with a string (NUL-terminated byte sequence) it begins with
"str". And it _is_ copying, but not into another string.

It is special purpose but perfectly reasonable for the problem at hand.
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

If it ain't broken, keep playing with it.