Question 1

Is Sparsepp faster than std::unordered_map?

Accepted Answer

Yes, benchmarks in the README show Sparsepp typically outperforms std::unordered_map in both speed and memory usage, thanks to its open addressing approach and efficient resizing that avoids large memory spikes.

Question 2

How do I handle custom hash functions with Sparsepp?

Accepted Answer

You can provide a hash function via the HashFcn template parameter or specialize std::hash for your class, using spp::hash_combine from sparsepp/spp_utils.h to combine fields, as illustrated in the Person struct example.

Question 3

What happens to iterators when I erase elements in Sparsepp?

Accepted Answer

Iterators are often invalidated on erase, but the erase function returns an iterator to the next element, allowing safe traversal and deletion. This differs from std::unordered_map where iterators might remain valid depending on the implementation.

Question 4

Sparsepp vs parallel hashmap: which one should I choose?

Accepted Answer

The author recommends parallel hashmap for most cases as it offers significantly better speed with slightly higher memory usage. Use Sparsepp only if you need the lowest memory overhead or are stuck with non-C++11 compilers.

Question 5

How to serialize a hash map using Sparsepp?

Accepted Answer

Implement a serializer class with operator() for your data types, then call map.serialize(serializer, stream). The README provides a full FileSerializer example using stdio, demonstrating how to save and load hash map data efficiently.

Question 6

Does Sparsepp work well on Windows?

Accepted Answer

Yes, it's tested on Windows with Visual Studio 2010-2015, but be cautious with the SPP_USE_SPP_ALLOC flag—it helps with large maps but can increase memory for small ones due to allocator fragmentation.

sparsepp

What is sparsepp?

Overview

Use Cases

Best For

Related Projects

Found a gem we're missing?

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions