Retrieving two chars from unsigned char *

[Seth]

I have a unsigned char *data that points to a 32 character string. I
need to retrieve 2 characters in the middle of the string.

What is the best way to do this?
Platform is embedded 8-bit atmel processor.

Thanks

[Eric Sosman]

Seth wrote:

I have a unsigned char *data that points to a 32 character string. I
need to retrieve 2 characters in the middle of the string.

What is the best way to do this?
Platform is embedded 8-bit atmel processor.

unsigned char *data = ...whatever...;
unsigned char c1 = data[15];
unsigned char c2 = data[16];

This should work on all processors: Atmel, Hormel,
and Wilhelmtell.

--
Eric Sosman
es*****@ieee-dot-org.invalid

[Seth]

Thanks a lot.
On a related note when I am comparing two unsigned char with strcmp I
get:
warning: pointer targets in passing argument 2 of 'strcmp' differ in
signedness

Should I be worried about this?

Thanks

On Jul 25, 11:25*pm, Eric Sosman <[e-mail] e:

Seth wrote:

I have a unsigned char *data that points to a 32 character string. I
need to retrieve 2 characters in the middle of the string.

What is the best way to do this?
Platform is embedded 8-bit atmel processor.

* * * * unsigned char *data = ...whatever...;
* * * * unsigned char c1 = data[15];
* * * * unsigned char c2 = data[16];

* * *This should work on all processors: Atmel, Hormel,
and Wilhelmtell.

--
Eric Sosman
[e-mail]

[santosh]

Seth wrote:

Thanks a lot.
On a related note when I am comparing two unsigned char with strcmp I
get:
warning: pointer targets in passing argument 2 of 'strcmp' differ in
signedness

Should I be worried about this?

Thanks

If you array is composed solely of the characters specified in the basic
character set, then you needn't be worried. If your array may consist
of any byte value then interpreting an unsigned value as a signed value
may cause overflow and undefined behaviour.

[rahul]

On Jul 26, 9:14*am, Seth <king.s...@gmai l.comwrote:

Thanks a lot.
On a related note when I am comparing two unsigned char

I take it that you meant to say "comparing two unsigned char *"

Should I be worried about this?

Depends on you charset. If you are using ASCII, no reasons to worry
about that.

[Harald van =?UTF-8?b?RMSzaw==?=]

On Fri, 25 Jul 2008 21:14:12 -0700, Seth wrote:

On a related note when I am comparing two unsigned char with strcmp I
get:
warning: pointer targets in passing argument 2 of 'strcmp' differ in
signedness

Should I be worried about this?

You need to cast them to char * and not rely on an implicit conversion
your compiler happens to support. Other than that, no, you don't need to
worry about it. strcmp works with unsigned char * anyway: it converts its
parameters from char * back to unsigned char * before reading the strings.

[vippstar]

On Jul 26, 10:26 am, rahul <rahulsin...@gm ail.comwrote:

On Jul 26, 9:14 am, Seth <king.s...@gmai l.comwrote:Than ks a lot.

Should I be worried about this?

Depends on you charset. If you are using ASCII, no reasons to worry
about that.

Please explain why ASCII matters (hint: it doesn't)

[vippstar]

On Jul 26, 10:39 am, vipps...@gmail. com wrote:

On Jul 26, 10:26 am, rahul <rahulsin...@gm ail.comwrote:

On Jul 26, 9:14 am, Seth <king.s...@gmai l.comwrote:>

Thanks a lot.
Should I be worried about this?

Depends on you charset. If you are using ASCII, no reasons to worry
about that.

Please explain why ASCII matters (hint: it doesn't)

I think I snipped context here.
Anyway the discussion was about pointer signedness passed to strcmp().
OP asked if it did matter and rahul suggested that if ASCII is
available it doesn't matter.
This code is perfectly valid,

....
unsigned char p[] = "hello", s[] = "world";

if(strcmp(p, s)) printf("They match!\n");
....

As is

if(strcmp((void *)p, (void *)s)) printf("They match!\n");

Though the latter will make (most) compilers not warn.

[Ike Naar]

In article <71************ *************** *******@w7g2000 hsa.googlegroup s.com>,
<vi******@gmail .comwrote:

>Anyway the discussion was about pointer signedness passed to strcmp().
OP asked if it did matter and rahul suggested that if ASCII is
available it doesn't matter.
This code is perfectly valid,

...
unsigned char p[] = "hello", s[] = "world";

if(strcmp(p, s)) printf("They match!\n");
...

strcmp returns 0 if the strings match:

if (0 == strcmp(p, s)) printf("They match!\n");

[vippstar]

On Jul 26, 11:05 am, i...@localhost. claranet.nl (Ike Naar) wrote:

<vipps...@gmail .comwrote:

if(strcmp(p, s)) printf("They match!\n");
...

strcmp returns 0 if the strings match:

if (0 == strcmp(p, s)) printf("They match!\n");

Heh. I wanted printf to print "They don't match!\n" though halfway I
forgot about it :P