I have to find the count of a substring in a string using the C language.
I'm using the function strstr but it only finds the first occurrence.
My idea of the algorithm is something like searching in the string while strstr does not return null and
to substring the main string on each loop.
My question is how to do that?
The results can be different depending whether you allow an overlap or not:
// gcc -std=c99
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
static int
count_substr(const char *str, const char* substr, bool overlap) {
if (strlen(substr) == 0) return -1; // forbid empty substr
int count = 0;
int increment = overlap ? 1 : strlen(substr);
for (char* s = (char*)str; (s = strstr(s, substr)); s += increment)
++count;
return count;
}
int main() {
char *substrs[] = {"a", "aa", "aaa", "b", "", NULL };
for (char** s = substrs; *s != NULL; ++s)
printf("'%s' -> %d, no overlap: %d\n", *s, count_substr("aaaaa", *s, true),
count_substr("aaaaa", *s, false));
}
'a' -> 5, no overlap: 5
'aa' -> 4, no overlap: 2
'aaa' -> 3, no overlap: 1
'b' -> 0, no overlap: 0
'' -> -1, no overlap: -1