How to locate the first occurrence of a string in a string

How to locate the first occurrence of a string in a string

I need a function like memchr() but it should be able to locate a
substring(string), not an only single char. And it should return the first
occurrence found in string.
For example
p1 = afunclikememchr(str1,"here the function can localize this
substring",200);
To the mods: I added the C++ tag because this is also relevant to C++
In a nutshell; I want a function that should be called like memstr