RapidJSON
A fast JSON parser/generator for C++ with both SAX/DOM style API
...Its performance can be comparable to strlen(). It also optionally supports SSE2/SSE4.2 for acceleration. RapidJSON is self-contained and header-only. It does not depend on external libraries such as BOOST. It even does not depend on STL. RapidJSON is memory-friendly. Each JSON value occupies exactly 16 bytes for most 32/64-bit machines (excluding text string). By default it uses a fast memory allocator, and the parser allocates memory compactly during parsing. RapidJSON is Unicode-friendly. It supports UTF-8, UTF-16, UTF-32 (LE & BE), and their detection, validation and transcoding internally. ...