Depends where you live. I have given money to homeless people three times in my life, all while I was a child. All three times, my generosity was met with "don't you have any more". I've learned my lesson, at least.

Here, the social safety net is giving these people more than enough to pay for the homeless shelter and groceries. My change isn't going to buy them anything the government isn't allowing them to buy anyway. Sure, there are lots of things that can be improved about the safety net (and the housing, and everything else), but you don't need to go hungry here.

I'm no longer giving money to beggars. If you want to help, fund local charities. Donating stuff is often appreciated, but what charities really need to help is cold hard cash, so that's the best way to help the most people.

Also be wary of beggar gangs if they're active in your country. Some criminal organisations will send out children, women, and anyone looking sad and unfortunate enough in an attempt to get strangers to donate money to them. A well-placed beggar can earn way more than a day's wage, and criminals are eager to abuse that.

If your country doesn't have a good social safety net, I'd still donate to charities before I'd give any money to the homeless directly, but it does change the situation a lot. I guess it depends on how good the local charities are (i.e. are they money hogs, do they require people to join their religion for aid, are they corrupt).