Comparing JSON Parse Trees

by Chad Austin on January 25th, 2013
I will soon post performance benchmarks of sajson, rapidjson, vjson, YAJL, and Jansson. However, before talking about performance, I want to compare the parse trees generated by each library.

sajson

  • Differentiates between integers and doubles
  • Array lengths are known.
  • Arrays are random-access.
  • Object lengths are known.
  • Object keys are sorted.  Thus, random access of object elements is O(lg N).
  • Stored contiguously in memory.

rapidjson

  • At its root, rapidjson is a SAX-style parser.  However, rapidjson does provide a default DOM implementation.
  • Array and Object length are not directly accessible in the API but are accessible via <code>End() – Begin()</code> or <code>MemberBegin() – MemberEnd()</code>.
  • Arrays support random access.
  • Object lookup is O(N).
  • Differentiates between integers, unsigned integers, 64-bit integers, 64-bit unsigned integers, and doubles.
  • Parse tree is mutable.

vjson

  • Namespaces its symbols under the generic “json” prefix.
  • Differentiates between integers and floats.  No support for doubles.
  • Array and Object lengths are not stored.  Instead a linked list must be traversed to calculate the length.
  • Random array access is O(N).
  • Object element lookup is O(N), by walking a linked list.
  • Very simple interface.

YAJL

  • Differentiates between integers and doubles.
  • Array and Object lengths are available.
  • Object element lookup is O(N).
  • Parse tree is mutable.

Jansson

  • Differentiates between integers and doubles.
  • Array and Object lengths are available.
  • Array access is O(1).
  • Object element access is O(1) via a hash table.
  • The parse tree is mutable.

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