To reverse a string

[sudharsan]

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance

[A. Sinan Unur]

"sudharsan" <su*********@gm ail.com> wrote in news:1142873798 .329339.167240
@e56g2000cwe.go oglegroups.com:

could any one please give me a code to reverse a string of more than
1MB .???

I can think of several reasons why the length of the string might be
important, but why does it matter to you?

Is the strlen to find the end of the string bothering you?

Have you tried the trivial way of doing it in place for a string of any
size?

Sinan
--
A. Sinan Unur <1u**@llenroc.u de.invalid>
(remove .invalid and reverse each component for email address)

comp.lang.perl. misc guidelines on the WWW:
http://mail.augustmail.com/~tadmc/cl...uidelines.html

[Vladimir S. Oka]

sudharsan 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?

--
BR, Vladimir

I'll meet you... on the dark side of the moon...
-- Pink Floyd

[santosh]

sudharsan wrote:

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance

Many C library implementations provide a non-standard strrev() function
which does what you want. If not, then you'll have to roll your own.
The size of the string shouldn't be a consideration if you're doing
this to learn programming or C. If you can implement the function is a
readable and straightforward manner and post your attempt here, the
regulars can help you further. It's quite easy to do.

[Richard G. Riley]

On 2006-03-20, sudharsan <su*********@gm ail.com> wrote:

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance

wtrite some code to reverse a string that works for 0,1,2 and 3
characters and it will probably work for a megabyte of them too. size
is no indicator of complexity.

[santosh]

sudharsan wrote:

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance

Here's one way of doing it.
NOTE: If your implementation already defines a strrev() function, then
rename the corresponding function in the following code to avoid linker
errors.

#include <stddef.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

bool strrev( char *s ) {
char tmp, *adv_p = NULL, *reg_p = NULL;
size_t l = 0;
ptrdiff_t seperation = 0;

if(s == NULL || (l = strlen(s)) < 2)
return false;
else {
adv_p = s;
--l;
reg_p = adv_p + l;
}

do {
tmp = *adv_p;
*adv_p = *reg_p;
*reg_p = tmp;
++adv_p;
--reg_p;
seperation = reg_p - adv_p;
} while(seperatio n > 0);

return true;
}

int main(void) {
char arr[32];

puts("Please enter your name:");
if(fgets(arr, 32, stdin) == NULL)
return EXIT_FAILURE;
else {
if(!strrev(arr) )
puts("strrev() returned false.");
else
printf("Your name reversed:\n%s\n ", arr);
}

return EXIT_SUCCESS;
}

[A. Sinan Unur]

"santosh" <sa*********@gm ail.com> wrote in news:1142879921 .107221.266900
@g10g2000cwb.go oglegroups.com:

sudharsan wrote:

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance
Here's one way of doing it.
NOTE: If your implementation already defines a strrev() function, then
rename the corresponding function in the following code to avoid
linker errors.

#include <stddef.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

bool strrev( char *s ) {
char tmp, *adv_p = NULL, *reg_p = NULL;
size_t l = 0;
ptrdiff_t seperation = 0;

separation
if(s == NULL || (l = strlen(s)) < 2)
return false;

Passing a NULL to this function is a violation of contract, it seems to
me. I would have been inclined to code that requirement into an assert.

On the other hand, passing an empty string or a string consisting of a
single character is benign. I would have just returned from this
function upon detecting that.

Are you using the return value as a 'success' indicator? In that case,
why is it an error condition to not modify the passed string?

Sinan

--
A. Sinan Unur <1u**@llenroc.u de.invalid>
(remove .invalid and reverse each component for email address)

comp.lang.perl. misc guidelines on the WWW:
http://mail.augustmail.com/~tadmc/cl...uidelines.html

[santosh]

A. Sinan Unur wrote:

"santosh" <sa*********@gm ail.com> wrote in news:1142879921 .107221.266900
@g10g2000cwb.go oglegroups.com:

sudharsan wrote:

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance
Here's one way of doing it.
NOTE: If your implementation already defines a strrev() function, then
rename the corresponding function in the following code to avoid
linker errors.

#include <stddef.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

bool strrev( char *s ) {
char tmp, *adv_p = NULL, *reg_p = NULL;
size_t l = 0;
ptrdiff_t seperation = 0;

separation

if(s == NULL || (l = strlen(s)) < 2)
return false;

Passing a NULL to this function is a violation of contract, it seems to
me. I would have been inclined to code that requirement into an assert.

Maybe your right. An assert() though would abort the program. What if
the caller may need to do other tasks, even if this function fails?
On the other hand, passing an empty string or a string consisting of a
single character is benign. I would have just returned from this
function upon detecting that.
Yes. You're right. I should probably just return true with 's'
unmodified. In that case I should seperate the tests for null pointer
and empty or single character string.
Are you using the return value as a 'success' indicator?
Yes.
In that case, why is it an error condition to not modify the passed string?

It shouldn't be. It was a decision on the spur of the moment. I'll
change it.
Thanks for your feedback.

[Richard G. Riley]

On 2006-03-20, santosh <sa*********@gm ail.com> wrote:

sudharsan wrote:

could any one please give me a code to reverse a string of more than
1MB .???
Thanks in advance
Here's one way of doing it.
NOTE: If your implementation already defines a strrev() function, then
rename the corresponding function in the following code to avoid linker
errors.

#include <stddef.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

bool strrev( char *s ) {
char tmp, *adv_p = NULL, *reg_p = NULL;
size_t l = 0;
ptrdiff_t seperation = 0;

if(s == NULL || (l = strlen(s)) < 2)
return false;

It's legal to reverse a string of one character. Or does "false" just
indicate no reversal was necessary?
else {
Its all an else in this case since you returned.

adv_p = s;
--l;
reg_p = adv_p + l;
}

do {
tmp = *adv_p;
*adv_p = *reg_p;
*reg_p = tmp;
++adv_p;
--reg_p;
seperation = reg_p - adv_p;
} while(seperatio n > 0);

return true;
}
nicer just to use the strlen/2 IMO.

void reverse(char * refS){
/* assume parent does parameter checks */
unsigned int len = (unsigned int)strlen(refS );
char * refE=refS+len-1; /* if len is 0 no problem since nothing done*/
len=len/2; /* or len>>=1 */
while(len--){
char c = *refS; /* front char */
*refS++ = *refE; /* is now end char */
*refE-- = c; /* end char now start char */
}
}


int main(void) {
char arr[32];

puts("Please enter your name:");
if(fgets(arr, 32, stdin) == NULL)
return EXIT_FAILURE;
else {
if(!strrev(arr) )
puts("strrev() returned false.");
else
printf("Your name reversed:\n%s\n ", arr);
}

return EXIT_SUCCESS;
}

--
Debuggers : you know it makes sense.
http://heather.cs.ucdavis.edu/~matlo...g.html#tth_sEc

[A. Sinan Unur]

"Richard G. Riley" <rg****@gmail.c om> wrote in news:tub3f3-03i.ln1
@fujitsu.mydoma in.com:

void reverse(char * refS){
/* assume parent does parameter checks */
unsigned int len = (unsigned int)strlen(refS );

size_t len = strlen(refS);

Sinan

--
A. Sinan Unur <1u**@llenroc.u de.invalid>
(remove .invalid and reverse each component for email address)