bsearch and searching range?

Question

bsearch is pretty good for direct search, but what should I use if I need for example search range?

update

for example if i want to find range of values between a and b ( a >= x < b ).

update

range values can be not equal. so if i have array(10,20,30) and i'm trying to find "15" i want to get address (pointer) to minimal range that is closest, in this example this is range (10,20)