What is memory fragmentation?

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I've heard the term "memory fragmentation" used a few times in the context of C++ dynamic memory allocation. I've found some questions about how to deal with memory fragmentation, but can't find a direct question that deals with it itself. So:

  • What is memory fragmentation?
  • How can I tell if memory fragmentation is a problem for my application? What kind of program is most likely to suffer?
  • What are good common ways to deal with memory fragmentation?

Also:

  • I've heard using dynamic allocations a lot can increase memory fragmentation. Is this true? In the context of C++, I understand all the standard containers (std::string, std::vector, etc) use dynamic memory allocation. If these are used throughout a program (especially std::string), is memory fragmentation more likely to be a problem?
  • How can memory fragmentation be dealt with in an STL-heavy application?
fragmentation heap-memory memory c++
12 Answers

What kind of program is most likely to suffer?

A nice (=horrifying) example for the problems associated with memory fragmentation was the development and release of "Elemental: War of Magic", a computer game by Stardock.

The game was built for 32bit/2GB Memory and had to do a lot of optimisation in memory management to make the game work within those 2GB of Memory. As the "optimisation" lead to constant allocation and de-allocation, over time heap memory fragmentation occurred and made the game crash every time.

There is a "war story" interview on YouTube.

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