Hey Tiger! They don't have the same meaning. The word shameless usually describes someone who should feel shameful, but appear not to. E.g. if someone has done something wrong, and seems to be unaffected by it, they are shameless. If they show remorse, they are shameful. Hope I was able to explain it somewhat. - prebs

Hi Tiger, Preben gave you a fine answer! I'll make it simpler: the words (shameless and shameful) come from shame, so shame+less is without shame; on the contrary shame +ful means full of shame. It helps to understand the meaning of the word. If you think this way, it can help you every time you meet words with -less and -ful. I hope I was help-ful!!