string compare

[yeti]

Hi guys,

I am using custom string structures in a project.

typedef struct{
short int length;
char data[256];
}my_long_string;

and

typedef struct{
short int length;
char data[32];
}my_short_string;

I want to create string processing functions like strcmp, strcpy etc
for these types.

While I can create different functions for these two types, is there
any way to use same function to handle both types ??
With C++ this would have been easy ... I'd have to just overload a
function, but since function overloading is not supported in C is
there a way/technique which I can use to simulate similar behaviour ??

regards

Rohin

[jacob navia]

yeti wrote:

Hi guys,

I am using custom string structures in a project.

typedef struct{
short int length;
char data[256];
}my_long_string;

and

typedef struct{
short int length;
char data[32];
}my_short_string;

I want to create string processing functions like strcmp, strcpy etc
for these types.

While I can create different functions for these two types, is there
any way to use same function to handle both types ??
With C++ this would have been easy ... I'd have to just overload a
function, but since function overloading is not supported in C is
there a way/technique which I can use to simulate similar behaviour ??

regards

Rohin

You can download such a library from the lcc-win download
site. It uses the proposed extensions of lcc-win for the C language.

That string library features Strcmp, Strcat, etc.

Source code is included
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32

[Malcolm McLean]

"yeti" <ro********@gmail.comwrote in message

>
I am using custom string structures in a project.

typedef struct{
short int length;
char data[256];
}my_long_string;

and

typedef struct{
short int length;
char data[32];
}my_short_string;

I want to create string processing functions like strcmp, strcpy etc
for these types.

While I can create different functions for these two types, is there
any way to use same function to handle both types ??
With C++ this would have been easy ... I'd have to just overload a
function, but since function overloading is not supported in C is
there a way/technique which I can use to simulate similar behaviour ??

Sadly no.
You are creating an N squared problem as you add more string types. Ypu can
get round it by converting everything to an intermediate type, but then you
will lose the speed that was the motive for the new types in the first
place.

--
Free games and programming goodies.
http://www.personal.leeds.ac.uk/~bgy1mm

[Mark Bluemel]

yeti wrote:

On Jan 23, 11:48 am, santosh <[e-mail]:

>yeti wrote:

>>Hi guys,
I am using custom string structures in a project.
typedef struct{
short int length;
char data[256];
}my_long_string;
and
typedef struct{
short int length;
char data[32];
}my_short_string;

....

>... I would make the types dynamic to start with, so that multiple types
can be avoided. Then the array can grow as needed.

Creating the types dynamic would put in problems like memory leaks. I
don't think it would be safe.

I think Santosh was suggesting a structure approach like this :-

typedef struct {
short length;
char data[]; /* or "char data[1];" if c99 support isn't available */
} my_string;

so if you had a string of 32 characters to work with, you'd do something
like:-

my_string *string_pointer = malloc(sizeof(short) + 32);
/* check the return value */

string_pointer->length = 32;
memcpy(string_pointer->data,<some source>,32);

I'm not sure what risks you perceive in this approach.

[Flash Gordon]

jacob navia wrote, On 23/01/08 08:24:

yeti wrote:

>Hi guys,

I am using custom string structures in a project.

typedef struct{
short int length;
char data[256];
}my_long_string;

<snip>

You can download such a library from the lcc-win download
site. It uses the proposed extensions of lcc-win for the C language.

That string library features Strcmp, Strcat, etc.

Source code is included

Note that as it relies on an extension which is, to the best of my
knowledge, unique to lcc-win you will only be able to use the library if
you are prepared to restrict yourself to lcc-win.
--
Flash Gordon

[Army1987]

yeti wrote:

Hi guys,

I am using custom string structures in a project.

typedef struct{
short int length;
char data[256];
}my_long_string;

and

typedef struct{
short int length;
char data[32];
}my_short_string;

I want to create string processing functions like strcmp, strcpy etc
for these types.

If offsetof(my_long_string, data) equals offsetof(my_short_string, data)
you can do:

int my_strcmp(const void *a, const void *b)
{
short int a_length = *(const short int *)a;
short int b_length = *(const short int *)b;
const char *a_data = (const char *)a + offsetof(my_long_string, data);
const char *b_data = (const char *)b + offsetof(my_long_string, data);
if (a_length < b_length)
return -1;
else if (a_length b_length)
return +1;
else
return memcmp(a_data, b_data, a_length);
}

void my_strcpy(void *target, const void *source)
{
*(short int *)target = *(const short int *)source;
memcpy((char *)target + offsetof(my_long_string, data),
(const char *)target + offsetof(my_long_string, data),
*(const short int *)source);
}
Of course, it causes UB if you try to copy a string larger than the
destination array, but so does the "real" strcpy.

--
Army1987 (Replace "NOSPAM" with "email")

[=?UTF-8?q?Harald_van_D=C4=B3k?=]

On Thu, 07 Feb 2008 06:51:13 +0000, James Antill wrote:

On Wed, 30 Jan 2008 15:32:54 -0800, jameskuyper wrote:

>James Antill wrote:

>>On Wed, 23 Jan 2008 13:08:14 +0000, James Kuyper wrote:
Mark Bluemel wrote:
typedef struct {
short length;
char data[]; /* or "char data[1];" if c99 support isn't
available */
} my_string;

#include <stddef.h>
...
mystring *string_pointer = malloc(offsetof(my_string, data) +
32);

This is required to be the same as sizeof(mystring),

Citation, please?

6.7.2.1

#16

As a special case, the last element of a structure with more than one
named member may have an incomplete array type; [...] the size of the
structure shall be equal to the offset of the last element of an
otherwise identical structure that replaces the flexible array member
with an array of unspecified length

This states that sizeof(my_string) must be equal to offsetof(struct {
short length;
char data[n];
}, data) for some fixed n, but that might be different from
offsetof(my_string, data).

#17 even gives an example basically identical to what I posted.

#17 even explicitly mentions that the offset of a flexible array member
might differ from the offset of a non-flexible array member.