help with snippet from c-faq.com

[Mark]

Hi

take a look at http://c-faq.com/misc/hexio.html, specifically at:

static char retbuf[33];
char *p;
p = &retbuf[sizeof(retbuf)-1];
....

Why do we have to keep additional pointer 'p' to a 'retbuf'? If we fill in
the 'retbuf' and then return it from the function ('return retbuf'), it will
always point at the very first element of the buffer, and we can safely use
from the caller.

Am I wrong?

 

[Ben Pfaff]

take a look at http://c-faq.com/misc/hexio.html, specifically at:

static char retbuf[33];
char *p;
p = &retbuf[sizeof(retbuf)-1];
...

Why do we have to keep additional pointer 'p' to a 'retbuf'? If we
fill in the 'retbuf' and then return it from the function ('return
retbuf'), it will always point at the very first element of the
buffer, and we can safely use from the caller.

The function doesn't always fill in the whole buffer. Most of
the time it only fills in the last few bytes. In such a case,
returning retbuf would return garbage.

 

[Ian Collins]

Hi

take a look at http://c-faq.com/misc/hexio.html, specifically at:

static char retbuf[33];
char *p;
p = &retbuf[sizeof(retbuf)-1];
....

Why do we have to keep additional pointer 'p' to a 'retbuf'? If we fill
in the 'retbuf' and then return it from the function ('return retbuf'),
it will always point at the very first element of the buffer, and we can
safely use from the caller.

Read the reset of the function!

The buffer is filled from the end.

 

[Mark]

static char retbuf[33];
char *p;
p = &retbuf[sizeof(retbuf)-1];
...

Why do we have to keep additional pointer 'p' to a 'retbuf'? If we
fill in the 'retbuf' and then return it from the function ('return
retbuf'), it will always point at the very first element of the
buffer, and we can safely use from the caller.

The function doesn't always fill in the whole buffer. Most of
the time it only fills in the last few bytes. In such a case,
returning retbuf would return garbage.

I see now, function fills in the output buffer starting from its *end*.
Thank you for clarifying this to me.