count the number of occurrences of a substring in a string

[sibingpeter]

Hi there,

Im trying to find the right way to code the loop to count the number of
occurences of a given substring in a string. Im able to find the first
occurence using the strstr function, but I just cant seem to think of
the right loop that would continue searching after finding this first
occurence. Could someone please help me out here?

 

[Charles Mills]

Hi there,

Im trying to find the right way to code the loop to count the number of
occurences of a given substring in a string. Im able to find the first
occurence using the strstr function, but I just cant seem to think of
the right loop that would continue searching after finding this first
occurence. Could someone please help me out here?

I think this is OK:

int
count_strinstr(const char *big, const char *little)
{
const char *p;
int count = 0;
size_t lil_len = strlen(little);

/* you decide what to do here */
if (lil_len == 0) return -1;

p = strstr(big, little);
while (p) {
count++;
p = strstr(p + lil_len, little);
}
return count;
}

If either arg is NULL this will probably barf.

-Charlie

 

[Barry]

I think this is OK:

int
count_strinstr(const char *big, const char *little)
{
const char *p;
int count = 0;
size_t lil_len = strlen(little);

/* you decide what to do here */
if (lil_len == 0) return -1;

p = strstr(big, little);
while (p) {
count++;
p = strstr(p + lil_len, little);
}
return count;
}

If either arg is NULL this will probably barf.

-Charlie

It depends on whether the occurrences have to be distinctly separate from
one another.
Consider:
little is "abab"
big is "ababababababab"

Barry

 

[sibingpeter]

Hey Charlie,

"p = strstr(p + lil_len, little);"

That addition of the string length was the logic that I was lookin for.
Thanks a lot for your help. Appreciate it.

 

[Malcolm]

"p = strstr(p + lil_len, little);"

That addition of the string length was the logic that I was lookin for.
Thanks a lot for your help. Appreciate it.

If you want to allow sustrings to overlap, add one to the pointer. If you
want to disallow this, add the length of the substring, as Charles showed
you.