c take a slice of an array by advancing the array -

i've got array of binary data in need count amount of times char sequence appears. @ moment defined function, find index of 'needle' in 'haystack'

int indexof(const char *needle, int needlelen, const char *haystack, int haystacklen) { /.../ } 

it returns -1 if needle can't found, otherwise returns index.

the next step run indexof in while-loop (till -1) count.

my question is: whenever found index in haystack, how take slice of haystack first char's determined indexof have been chomped off?

example: haystack hello_world, needle o. indexof return 4. how take slice of hello world without first 4 chars? e.g. want _world

my haystack hello_world, needle o. indexof return 4. how take slice of hello world without first 4 chars? e.g. want _world

if index 4, need skip first 5 characters (remember indexing in c 0 based).

that haystack + 4 + 1. remember update size of haystack accordingly, not access off end it.

or in c:

idx = indexof(needle, needlelen, haystack + idx + 1, haystacklen - idx - 1); 

where if idx 4, index 5 onward.