С поиск позиции подстроки

#include <stdio.h>
#include <string.h>
int main ()
{
  char str[] ="This is a line";
  char *p;
  p = strstr (str, "is");
  strncpy (p, "sample",5 );
  return 0;
}

#include <stdio.h>
#include <string.h>
int main ()
{
  char str[] ="This is a line";
  char *p;
  size_t found;
  found=strstr (str, "is");
  printf("Found: %i", int(found));
  return 0;
}

int inStr(char *pattern, char *str) {
        int i, foundPos = 0;
        /* stop looping at end of string */
        while(str[foundPos]!=0) {
                if (str[foundPos]==pattern[0]) {
                        /* our current search position matches
                        the first character in the pattern,
                        we'll look for more
                        */
                        i = 1;
                        /* we know i=0 is a match, so we start at 1
                        we loop until one of one of three conditions is met
                        1. we hit the end the pattern
                        2. we hit the end of the string
                        3. the characters are not equal
                        */
                        while(pattern[i]!=0 && str[foundPos + i]!=0 && str[foundPos + i]==pattern[i]) { i++; }
                        /* if we got the end of the pattern, we have a match */
                        if (pattern[i]==0) {
                                return foundPos;
                        /* if we got to the end of the search string, all other searches will fail too */
                        } else if (str[foundPos + i]==0) {
                                return -1;
                        }
                        /* if it just didn't match, we move on */
                }
                /* move our search one position forward and repeat */
                foundPos++;
        }
        /* if we got here, we found nothing */
        return -1;
}

#include <locale.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <regex.h>
#define ERRBUF_SIZE 1024
#define NMATCH 10
void error(int err_code, regex_t *rs)1
{
        char errbuf[ERRBUF_SIZE];
        if(!err_code)   return;
        regerror(err_code, rs, errbuf, ERRBUF_SIZE);
        fprintf(stderr, "regex error: %s\n", errbuf);
        regfree(rs);
        _exit(err_code);
}
int main(void)
{
        const char str[] = "тестов\xD1\xD1ая строчка. ABCDEFG";2
        const char regex[] = ".*";3
        regex_t rs;
        regmatch_t pmatch[NMATCH];
        char *lc = setlocale(LC_ALL, "ru_RU.UTF-8");4
        if(!lc)    return 77;
        printf("test string: `%s' (%s)\n", str, lc);
        int err = regcomp(&rs, regex, REG_EXTENDED);
        error(err, &rs);
        const char *ps = str;
        while(*ps)5
        {
                err = regexec(&rs, ps, NMATCH, pmatch, 0);
                error(err, &rs);
                int j;
                const char *ps2 = NULL;
                for(j = 0; j < NMATCH; j++)
                {
                        if(pmatch[j].rm_so < 0)
                                continue;
                        printf("Совпадение %d: %d...%d\t`", j, pmatch[j].rm_so, pmatch[j].rm_eo);
                        int i;
                        for(i = pmatch[j].rm_so; i < pmatch[j].rm_eo; i++)
                                printf("%c", ps[i]);
                        printf("'\n");
                        if(!ps2)
                                ps2 = ps + i;6
                }
                ps = ps2;
                if(!ps)    break;7
                printf("остаток: `%s'\n", ps);
        }
        regfree(&rs);
        return 0;
}