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Yet Another C JSON Parser.

Why yet another library

The incentive is always the same: existing ones don't suit me. I found some flaws in the better known cJSON library:

  • no way to directly read a file; one must first put it fully in a string, then call the parser, thus maybe consuming a lot of memory
  • a one-size-fits-all structure, with fields for all types of JSON values (mixed fields include next/previous links, children, strings, and numbers)
  • arrays and objects are implemented using linked objects, may cause performance problems

To fix those flaws, YacJP provides the following features:

  • JSON reading from many data streams (provided input streams include strings, files, and file descriptors)
  • JSON writing to data streams, with options such as compact vs. pretty output
  • an object-oriented approach, with well separated data structures, and actual encapsulation
  • AFAICS a better number support

On the other hand cJSON is small; YacJP is bigger (approx. 4000 lines, not counting tests; see the Statistics chapter).

The YacJP philosophy

C does not mean ``not object''. Actually the whole YacJP library is built using object-oriented techniques: one may find encapsulation, polymorphism, and even some design patterns (composites, factories, visitors).

YacJP is compact, but not at the price of extensibility and legibility.

YacJP is customizable: the user may provide specific hooks such as their own implementation of malloc(3) and free(3), a \ref json_on_error_fn "custom parse error handler", and so on.

YacJP is extendable: the user may provide their own implementation of \ref json_stream "input/output streams", as long as they provide the right interface they will be used correctly. Indeed, there is polymorphism in C.

YacJP is user-friendly: to implement actions on the JSON values tree, one just need to provide a \ref json_visitor "visitor" structure which is a list of functions, one for each data type (objects, arrays, and so on). Implementing such a structure is straightforward. There are examples of such implementations in YacJP itself:

  • the \ref json_kill "kill" visitor allows to correctly (recursively) free a whole JSON value tree;
  • the \ref json_write_to "write_to" visitor allows to write a JSON value tree to an output stream, with a few options such as the level of prettiness.


Yet Another C JSON Parser






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