c - Get index of substring

Question

I have char * source, and I want extract from it subsrting, that I know is beginning from symbols "abc", and ends where source ends. With strstr 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?

Answer 1

Use pointer subtraction.

char *str = "sdfadabcGGGGGGGGG";
char *result = strstr(str, "abc");
int position = result - str;
int substringLength = strlen(str) - position;