How do I get candle wax out of a glass jar?

I have several scented candles that are almost used up.

How can I safely get the last bit of wax out of the jars? I want to use some of them for planters or vases. But I have two I want to turn into candy/treat containers.

I have heard you can put them in a pot with hot water and melt the wax out. Will this ruin the pot for cooking? Will the jars then be safe to use for food?