Does log4cpp takes care of heap fragmentations issue?

Question

I develop on windows 64bit with VS2015.

I used a custom logger but it suffered from heap fragmentations. I found log4cpp library. According to the source code it uses std::ostringstream internally. My questions:

• I think my main question is can I use log4cpp safely and not worry about heap fragmentations?
• The first question probably leads to the questions how does std::ostringstream work internally to prevent heap fragmentations? Does it have multiple buffers in stack for small strings or does it always allocates a new string in heap?