occurrency in a string

Is there any function in C that counts the occurrency of a string within a string?

I need to know how many times a string is repeated within a string or a method to find out if groups of 2 or more words are repeated in a string.

I have already created a program that counts the number of occurrencies in a document using arrays but the analysis becomes complicated when I try to count groups of 2 or more words in a string.

thanks in advance for your comments