Number of times one string occurs within another in C - c

Question

I have written a function that uses the strstr() function to determine if string2 has any matches in string1. This works fine (I also convert both strings to lower case so that I can do a case-insensitive match.). However, strstr() only finds the first time the match occurs. Is there a way to use it to find each time a match occurs? For example:
string1[] = "ABCDEFABC";
string2[] = "ABC";
Would return 0 as a match is found in position 0, and 6 as it's found again in position 6?
Here's the original function as written (including call to function in main):
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char *strstrnc(const char *str1, const char *str2);
int main()
{
char buf1[80],buf2[80];
printf("Enter the first string to be compared: ");
gets(buf1);
printf("Enter the second string to be compared: ");
gets(buf2);
strstrnc(buf1,buf2);
return 0;
}
char *strstrnc(const char *buf1, const char *buf2)
{
char *p1, *ptr1, *p2, *ptr2, *loc;
int ctr;
ptr1 = malloc(80 * sizeof(char));
ptr2 = malloc(80 * sizeof(char));
p1 = ptr1;
p2 = ptr2;
for (ctr = 0; ctr < strlen(buf1);ctr++)
{
*p1++ = tolower(buf1[ctr]);
}
*p1 = '\0';
for (ctr = 0; ctr < strlen(buf2);ctr++)
{
*p2++ = tolower(buf2[ctr]);
}
*p2 = '\0';
printf("The new first string is %s.\n", ptr1);
printf("The new first string is %s.\n", ptr2);
loc = strstr(ptr1,ptr2);
if (loc == NULL)
{
printf("No match was found!\n");
}
else
{
printf("%s was found at position %ld.\n", ptr2, loc-ptr1);
}
return loc;
}

Answer 1

Given
char string1[] = "ABCDEFABC";
char string2[] = "ABC";
strstr(string1, string2) will return a pointer to the first element of string1.
Would return 0 as a match is found in position 0, and 6 as it's found again in position 6?
In order to check for multiple occurrences of string2 in string1, you'll have to call strstr multiple times with an offset from string1. E.g.
char* found = strstr(string1, string2);
while ( found != NULL )
{
// Search for string2 after applying an offset.
int offset = 1;
found = strstr(found+offset, string2);
}

Answer 2

I think this is what you need:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main(void){
char string1[] = "ABCDABCEFABC";
char string2[] = "ABC";
char *s1, *s2, *s3;
size_t lenstring1 = strlen(string1);
size_t lenstring2 = strlen(string2);
if (lenstring2 < 1){
printf("There is no substring found"); /* or what ever */
exit(1);
}
size_t i=0,j=0;
int found=0;
s1 = string1;
s2 = string2;
for(i = 0; i < lenstring1; i++){
if(*s1 == *s2){
s3 = s1;
for(j = 0;j < lenstring2;j++){
if(*s3 == *s2){
s3++;s2++;
}else{
break;
}
}
s2 = string2;
if(j == strlen(string2)){
found = 1;
printf("%s found at index : %zu\n",string2,i+1);
}
}
s1++;
}
if(found == 0){
printf("No match Found");
}
return 0;
}
Output:
ABC found at index : 1
ABC found at index : 5
ABC found at index : 10
If the string2 is empty you will get:
There is no substring found