could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance
Mar 20 '06
47  5026 
pete opined: Vladimir S. Oka wrote:
pete wrote: >>>>>pete wrote:
>>>>>>Vladimi r S. Oka wrote:
>>>>>
>>>>>>>sudharsa n opined:
>>>>>
>>>>>>>> could any one please give me a code to reverse a string of
>>>>>>>> more than 1MB .???
>>>>>
>>>>>>>Why do you think it would be different to
>>>>>>>the one for strings less than 1MB?
>>>>>
>>>>>>Because a conforming implementation of C,
>>>>>>is not required to be able to translate and execute
>>>>>>a program which excedes the minimum translation limits.
>>>>>
>>>>>>strlen isn't required to work right on a string that long.
>>>>>
>>>>>>The business in the standard about the ptrdiff_t type
>>>>>>not being guaranteed to be able to do its job,
>>>>>>is most appropriately applied to code with objects
>>>>>>which exceede the translation limits.
>>>>>>I've seen strlen implemented on this newsgroup
>>>>>>in ways which depend upon the ptrdiff_t type
>>>>>>being able to do its job.
>>>>>
>>>>>All you say is fine,
>>>>>but I don't see how it applies to your quote of
>>>>>what I said.
>>>>>
>>>>>Unless you took to the word "code" in the OP to meant "exact
>>>>>implementa tion detail",
>>>>>while I read it as "the [general] method". In
I took it to mean exact "implementa tion detail"
and the reason that I did,
is because the exact implementation detail
depends on the length of the string.
In which case we actually agree.
The difference in methodology,
depending on the length of the string, is a c language issue.
To me, "the [general] method" sounds like an algorithm issue.
This is a c language newsgroup, not an algorithm newsgroup.
Yes, but in this case they seem to be intertwined since C language
features have a bearing on the method chosen. In any case, I tend not
to /discuss/ algorithm issues here, but I do offer an odd idea.
>>>>>that case we actually agree,
>>>>>but are talking about diferent parts of
>>>>>the problem.
>>>>>
>>>>>The fact that you may have to implement your own `strlen()`, or
>>>>>whatever , to me, does not change the way this is done.
>>>>
>>>>To me, whether or not you have to implement your own strlen,
>>>>does change the way this is done.
>>>
>>>How so?
>>>
>>>> char *str_rev(char *s)
>>>> {
>>>> char *t, swap;
>>>> char *const p = s;
>>>>
>>>> if (*s != '\0') {
>>>> t = s + strlen(s + 1);
>>>
>>>What's wrong with:
>>>
>>> t = s + my_strlen(s + 1);
>>>
>>>> while (t > s) {
>>>> swap = *t;
>>>> *t-- = *s;
>>>> *s++ = swap;
>>>> }
>>>> }
>>>> return p;
>>>>
>>>> }
>>>
>>>It seems Chuck thinks the above doesn't work
>>> -- I didn't check myself.
Too bad that you didn't.
You could have opinion of your own about the code, if you had.
Admittedly, my comment was unnecessary, to say the least, and certainly
vacuous. I did not express /any/ opinion about your code, though.
Let's say I made a clumsy, and unnecessary reference to another post
that did.
>>Why would you write your own strlen to reverse a string,
>>instead of using the one in the standard library?
>>
>>I was replying to what you said earlier:
>>
>>> Because a conforming implementation of C,
>>> is not required to be able to translate and execute
>>> a program which excedes the minimum translation limits.
>>> strlen isn't required to work right on a string that long.
>>
>>Which you snipped.
>>
>>To expand:
>>if `strlen()` won't necessarilly work on huge strings (your
>>assertion above, I didn't check the Standard), then rolling your
>>own may help.
>
>That's the answer to your original question:
>
>"Why do you think it would be different to the one
> for strings less than 1MB?"
>
>This is a c language newsgroup, not an algorithm newsgroup.
I have now, painstaikingly, re-built the whole exchange. Without
snipping *anything* will you, please,
point to exact things that I said
that you have an issue with, and exactly why?
If you still feel I was grossly off-topic, I apologise, but beg to
disagree, and let's leave it at that.
--
BR, Vladimir
So far as I can remember, there is not one word in the Gospels in
praise of intelligence.
-- Bertrand Russell
pete wrote: CBFalconer wrote: pete wrote: Vladimir S. Oka wrote:
The fact that you may have to implement your own `strlen()`, or
whatever, to me, does not change the way this is done.
To me, whether or not you have to implement your own strlen,
does change the way this is done.
char *str_rev(char *s)
{
char *t, swap;
char *const p = s;
if (*s != '\0') {
t = s + strlen(s + 1);
while (t > s) {
swap = *t;
*t-- = *s;
*s++ = swap;
}
}
return p;
}
Er - that doesn't work. Check the boundary conditions.
I can't find a problem.
I spoke too quickly. It does work. Sorry.
Boundary conditions mean just that, in this case 0 length strings,
or because of the initial elimination 1 length strings.
--
Read about the Sony stealthware that is a security leak, phones
home, and is generally illegal in most parts of the world. Also
the apparent connivance of the various security software firms. http://www.schneier.com/blog/archive...drm_rootk.html
pete wrote: CBFalconer wrote:
.... snip ...
I hadn't thought about it at first,
but since your function returned length and mine didn't,
they were not really the same.
size_t str_rev(char *s)
{
char *t, swap;
size_t length;
if (s[0] != '\0') {
if (s[1] != '\0') {
length = strlen(s);
t = s + length - 1;
do {
swap = *t;
*t-- = *s;
*s++ = swap;
} while (t > s);
} else {
length = 1;
}
} else {
length = 0;
}
return length;
}
size_t revstring(char *stg)
{
char *last, temp;
size_t lgh;
lgh = strlen(stg);
if (lgh > 1) {
last = stg + lgh; /* points to '\0' */
while (last-- > stg) {
temp = *stg; *stg++ = *last; *last = temp;
}
}
return lgh;
} /* revstring */
Just for side by side comparison. The fundamental formatting is
the same, the only basic difference being that I use multiple
instructions per line to implement the "tradechars " operation. I
maintain my code is clearer, and probably generates more compact
object code, barring a very smart optimizer. It is certainly more
succint.
--
Read about the Sony stealthware that is a security leak, phones
home, and is generally illegal in most parts of the world. Also
the apparent connivance of the various security software firms. http://www.schneier.com/blog/archive...drm_rootk.html
Ben Pfaff wrote
(in article <87************ @benpfaff.org>) : ri*****@cogsci. ed.ac.uk (Richard Tobin) writes:
In article <ln************ @nuthaus.mib.or g>,
Keith Thompson <ks***@mib.or g> wrote:
> Draw yourself a picture of an arbitrary string and figure out how you'd
> reverse it in place. You should only need a single temporary.
You don't even need one - you can use the nul at the end of the
string...
Yes, if saving a single temporary object is worth writing abominably
ugly code.
I repeatedly see people people denouncing the use of smilies on the
grounds that intelligent readers don't need them, but I'm beginning
to doubt it.
You think the articles from folks who think XOR is a good way to
swap two variables are all jokes then?
They're always funny, even if the poster doesn't realize he is
making a joke of himself. :-)
--
Randy Howard (2reply remove FOOBAR)
"The power of accurate observation is called cynicism by those
who have not got it." - George Bernard Shaw
CBFalconer wrote: size_t revstring(char *stg)
{
char *last, temp;
size_t lgh;
lgh = strlen(stg);
if (lgh > 1) {
last = stg + lgh; /* points to '\0' */
while (last-- > stg) {
temp = *stg; *stg++ = *last; *last = temp;
}
}
return lgh;
} /* revstring */
Just for side by side comparison. The fundamental formatting is
the same, the only basic difference being that I use multiple
instructions per line to implement the "tradechars " operation. I
maintain my code is clearer, and probably generates more compact
object code, barring a very smart optimizer. It is certainly more
succint.
It swaps the middle element
of an odd length string with itself!
Holy redundancy Batman!
You have not a single thought to efficiency,
expressed in this code.
--
pete
pete wrote:
CBFalconer wrote:
size_t revstring(char *stg)
{
char *last, temp;
size_t lgh;
lgh = strlen(stg);
if (lgh > 1) {
last = stg + lgh; /* points to '\0' */
while (last-- > stg) {
temp = *stg; *stg++ = *last; *last = temp;
}
}
return lgh;
} /* revstring */
Just for side by side comparison. The fundamental formatting is
the same, the only basic difference being that I use multiple
instructions per line to implement the "tradechars " operation. I
maintain my code is clearer, and probably generates more compact
object code, barring a very smart optimizer. It is certainly more
succint.
It swaps the middle element
of an odd length string with itself!
Holy redundancy Batman!
You have not a single thought to efficiency,
expressed in this code.
size_t revstring(char *stg)
{
char *last, temp;
size_t lgh;
lgh = strlen(stg);
if (lgh > 1) {
last = stg + lgh - 1;
do {
temp = *stg; *stg++ = *last; *last-- = temp;
} while (last > stg);
}
return lgh;
} /* revstring */
--
pete
pete wrote: CBFalconer wrote:
size_t revstring(char *stg)
{
char *last, temp;
size_t lgh;
lgh = strlen(stg);
if (lgh > 1) {
last = stg + lgh; /* points to '\0' */
while (last-- > stg) {
temp = *stg; *stg++ = *last; *last = temp;
}
}
return lgh;
} /* revstring */
Just for side by side comparison. The fundamental formatting is
the same, the only basic difference being that I use multiple
instructions per line to implement the "tradechars " operation. I
maintain my code is clearer, and probably generates more compact
object code, barring a very smart optimizer. It is certainly more
succint.
It swaps the middle element of an odd length string with itself!
Holy redundancy Batman!
You have not a single thought to efficiency, expressed in this code.
If that really bothers you change last-- to --last.
--
Read about the Sony stealthware that is a security leak, phones
home, and is generally illegal in most parts of the world. Also
the apparent connivance of the various security software firms. http://www.schneier.com/blog/archive...drm_rootk.html
pete wrote:
.... snip ...
size_t revstring(char *stg)
{
char *last, temp;
size_t lgh;
lgh = strlen(stg);
if (lgh > 1) {
last = stg + lgh - 1;
do {
temp = *stg; *stg++ = *last; *last-- = temp;
} while (last > stg);
}
return lgh;
} /* revstring */
I think that works too, and is clear.
--
Read about the Sony stealthware that is a security leak, phones
home, and is generally illegal in most parts of the world. Also
the apparent connivance of the various security software firms. http://www.schneier.com/blog/archive...drm_rootk.html This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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