I'm having a little trouble in understanding how exactly Open Source licenses actually work. I have programmed for a while, but just for my personal use and I wrote all the code I needed myself.
As I'm thinking of making some apps for people and I need a fast XML parser, I thought I could use RapidXml. However, I'm not sure how it's going to be like under the license.
So, here's my question: if I use some code as part of my application, without any modification, how does it's license affect me? Exactly as if I was modifying it and distributing it? Do I have to publish my entire code?
Also, coding this app will require knowing the implementation of another open source project. Though, I'm going to write my code in a different language, i.e. I just need to know how it works for me to reproduce it. How does the license work here? (As a matter of fact, this one is GPLv3, and the other is not.)