You can't solve a problem like this with only examples of <. A
complete definition is necessary. For example, what do you do with
"a1" <>? "2b"
Report "mismatch?"
What do you do with
"1 abc" <>? "2 2"
Do you report < or mismatch?
Here is one of infinitely many complete definitions consistent with
your examples:
1. Split each string into lists of maximal tokens consisting of all
decimal digits or all letters. White space separates tokens but is
otherwise ignored. Anything other than digits, letters, and
whitespace is counted as end of string.
2. Call these lists A and B. Compare them pairwise. If Ai and Bi
are
both strings of letters, compare them lexically using UTF-8 order.
If
Ai and Bi are all digits, compare them numerically. Continue until
you find an inequality between a pair and report this immediately,
ignoring the rest of the string. If you find a pair with types
(letters or digits) that don't match, or if one token list is shorter
than the other, report "nothing." Otherwise if you run out of pairs,
report equal.
Here is code that is probably pretty close to this definition. Tasks
like this are easier if you split them up into a token scanning step
and a processing step. I've done that here.
#include <stdio.h>
#include <ctype.h>
// Scanner return values.
#define END 0
#define DIGITS 1
#define ALPHA 2
// Find the start and end of the first token
// beginning at *start, ignoring initial white space.
int scan(char **start, char **end)
{
char *p = *start;
while (isspace(*p)) ++p;
if (isdigit(*p)) {
*start = p;
do ++p; while (isdigit(*p));
*end = p;
return DIGITS;
}
if (isalpha(*p)) {
*start = p;
do ++p; while (isalpha(*p));
*end = p;
return ALPHA;
}
return END;
}
// Return the non-negative value of the string
// starting at p and ending at the char before end.
int int_value(char *p, char *end)
{
int x = 0;
while (p != end)
x = 10 * x + (*p++ - '0');
return x;
}
// Possible comparison values.
#define LT -1
#define EQ 0
#define GT 1
#define NOTHING 2
// Compare the strings starting at xp and ending
// one char before x_end where x is a or b.
int string_compare(char *ap, char *a_end,
char *bp, char *b_end)
{
while (ap < a_end && bp < b_end) {
int diff = *ap++ - *bp++;
if (diff < 0) return LT;
if (diff > 0) return GT;
}
if (bp < b_end) return LT;
if (ap < a_end) return GT;
return EQ;
}
// Compare tokens in strings a and b.
int compare(char *a, char *b)
{
char *a_end, *b_end;
while (1) {
int a_scan = scan(&a, &a_end);
int b_scan = scan(&b, &b_end);
if (a_scan != b_scan) return NOTHING;
if (a_scan == END) return EQ;
if (a_scan == DIGITS) {
int a_val = int_value(a, a_end);
int b_val = int_value(b, b_end);
if (a_val < b_val) return LT;
if (a_val > b_val) return GT;
}
else if (a_scan == ALPHA) {
int cmp = string_compare(a, a_end, b, b_end);
if (cmp != EQ) return cmp;
}
a = a_end;
b = b_end;
}
}
int main(void)
{
char *s[] = {
"a5", "a11",
"6xxx", "007asdf",
"00042Q", "42s",
"6 8", "006 9",
};
int i;
for (i = 0; i < sizeof s / sizeof s[0]; i += 2) {
int cmp = compare(s[i], s[i + 1]);
printf("%s %c %s\n", s[i], "<=>?"[cmp + 1], s[i + 1]);
}
return 0;
}
On Apr 17, 11:46 pm, "abhishek" <zeal.gosw...@gmail.com> wrote:
> Hi,
>
> I need to compare string into following way. Can anyone provide me some
> insight or algorithm in c++.
>
> For example:
>
> "a5" < "a11" - because 5 is less than 11
> "6xxx < 007asdf" - because 6 < 7
> "00042Q < 42s" - because Q < s alphabetically
> "6 8" < "006 9" - because 8 < 9
>
> Thx in advance
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