title: Get index of substring
body: <p>I have <strong>char * source</strong>, and I want extract from it subsrting, that I know is beginning from symbols "abc", and ends where source ends. With <strong>strstr</strong> I can get the poiner, but not the position, and without position I don't know the length of the substring. How can I get the index of the substring in pure C?</p>