replace by index - c

Question

I want to replace the string by index. The string between x and y. If the string that will be replaced the length is lees than y, the pointer must be incremented by the difference. e.g,
given the string ([10 20]...[10 20]..[30 80]); x = 1(index of [) and y = 7(index of ]), and the string-replace is 50, it must be replaced to (50...[10 20]..[30 80]).
I've tried it:
void replaceindex(char *s, char *replace, unsigned int start, unsigned int end)
{
assert(start < end);
char *p = s, *q = s, *r = replace;
register unsigned int i = 0;
int found = 0;
while(*q) {
if(found == 0 && i == start) {
found = 1;
for(; *r; ++r, ++start, ++q)
*p ++ = *r;
while(++start < end)
q++;
}
*p ++ = *q ++;
i ++;
}
}
using:
char str[] = "([10 20]...[10 20]..[30 80])";
printf("Before: %s\n", str);
replaceindex(str, "50", 1, 7);
printf("After: %s\n", str);
The output is:
Before: ([10 20]...[10 20]..[30 80])
After: (500]...[10 20]..[30 80])0])
But I'm expecting this:
Before: ([10 20]...[10 20]..[30 80])
After: (50...[10 20]..[30 80])
How to fix this?

Answer 1

Building on the ideas from Anon ymous, but avoiding the creation of a new string:
void replaceindex(char *s, char *replace, unsigned int start, unsigned int end)
{
unsigned rl, sl;
rl = strlen(replace);
sl = strlen(s);
++end; /* change inclusive index to exclusive one */
assert(start <= end);
assert(rl <= end - start);
memcpy(s + start, replace, rl);
memmove(s + start + rl, s + end, sl - end + 1);
}

Answer 2

You need two fixes:
for(; *r; ++r, ++start, ++q)
*p ++ = *r;
- while(++start < end)
+ while(start++ <= end)
q++;
}
*p ++ = *q ++;
i ++;
}
+ *p = '\0';
}
The first is because your end index is inclusive (judging from the call), and you want to compare first and increment afterwards. The second is to terminate the new string.
Note that you're in serious trouble if strlen(replace) > end - start + 1.

Answer 3

#include <stdio.h>
#include <string.h>
char* replaceindex(char *s, char *replace, unsigned int start, unsigned int end)
{
char *rep= (char*)malloc(strlen(s)+1);
memset(rep,0,strlen(s)+1);
if(strlen(replace)<=(end-start))
{ memcpy(rep,s,start);
memcpy(rep+start,replace,strlen(replace));
memcpy(rep+start+strlen(replace),s+end,strlen(s+end));
return rep;
}
else{free(rep);}
return s;
}
int main() {
char* z="This answer is crazy";
printf("%s",replaceindex(z,"Code",5,11));
return 0;
}
And the Output is
This Code is crazy
EDIT:
Without Memory:-
#include <stdio.h>
#include <string.h>
void replaceindex(char *s, char *replace, unsigned int start, unsigned int end)
{
if(strlen(replace)<=(end-start))
{
char* iter= s+start+strlen(replace),*cursor=s+end;
memcpy(s+start,replace,strlen(replace));
while(*iter)
*iter++=*cursor++;
}
}
int main()
{
char z[]="This answer is crazy";
replaceindex(z,"Code",5,11);
return printf("%s",z);
}