For fcc  if AB is just like the rock salt like structure then, A⁺ and B^- are located at 

${\mathrm{A}}^{+}\text{- Tetrahedral voids ; }{\mathrm{B}}^{-}\text{- Corner }$

${\mathrm{A}}^{+}\text{- Corner and faces };{\mathrm{B}}^{-}\text{- Octahedral voids }$

${\mathrm{A}}^{+}\text{- Octahedral voids };{\mathrm{B}}^{-}\text{- Corner and faces }$

${\mathrm{A}}^{+}$ - Corner and faces : ${\mathrm{B}}^{-}-\mathrm{O}$ctahedral and tetrahedral voice