Re: how to replace a substring in a string using C?

On Sun, 30 Oct 2005 19:45:30 +0000, Mike Wahler wrote:
> "Paul" <paul.pettus@xxxxxxxxx> wrote in message
> news:1130687985.367948.20180@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> hi, there,
>>
>> for example,
>>
>> char *mystr="##this is##a examp#le";
>>
>> I want to replace all the "##" in mystr with "****". How can I do this?

Your code looked fine Mike but I gathered the OP wanted to deal more
generally with string rather than character replacement, so here's an
extended version.

Output:

##this is##a examp#le
****this is****a examp#le

Code:

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

char *replace(const char *s, const char *old, const char *new)
{
char *ret;
int i, count = 0;
size_t newlen = strlen(new);
size_t oldlen = strlen(old);

for (i = 0; s[i] != '\0'; i++) {
if (strstr(&s[i], old) == &s[i]) {
count++;
i += oldlen - 1;
}
}

ret = malloc(i + count * (newlen - oldlen));
if (ret == NULL)
exit(EXIT_FAILURE);

i = 0;
while (*s) {
if (strstr(s, old) == s) {
strcpy(&ret[i], new);
i += newlen;
s += oldlen;
} else
ret[i++] = *s++;
}
ret[i] = '\0';

return ret;
}

int main(void)
{
char mystr[] = "##this is##a examp#le";
char *newstr = NULL;

puts(mystr);
newstr = replace(mystr, "##", "****");
printf("%s\n", newstr);

free(newstr);
return 0;
}

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