simpleson

Lightweight C++ JSON parser & serializer that is C++98 compatible with no dependencies

Why simpleson?

Simpleson is built under the following requirements:

One header and one source file only
No external dependencies
ISO/IEC 14882:1998 (aka C++98) compatible
Cross-platform

A primary use case for simpleson is in an memory-constrained embedded system.

Building simpleson

Simpleson was intentionally built such that a developer could simply copy json.h into the target project's inc folder, copy json.cpp into the src folder, and then compile the target project. No linking -> no drama.

Building the library and tests follows the standard build chain via CMake:

mkdir build
cd build
cmake ../
make

Unit tests can then be run by executing make test

Quickstart

// Create the input
std::string input = "{ \"hello\": \"world\" }";

// Parse the input
json::jobject result = json::jobject::parse(input);

// Get a value
std::string value = (std::string)result.get_entry("hello").value

// Add entry
json::key_value_pair item;
item.key = "new_key";
item.value = json::jvalue(123.4);
result.push_back(item);

// Serialize the new object
std::string serial = (std::string)result;

Using simpleson

The namespace of simpleson is simply json. JSON objects can be parsed by calling json::jobject::parse(), which returns a jobject. The jobject class is simply an extension of a vector of key-value pairs. Useful methods of jobject include:

has_key("key")
get_keys()
get_entry("key")

An instance of jobject can be searlized by casting it to a std::string. Note that an instance of jobject does not retain it's original formatting (it drops tabs, spaces outside strings, and newlines).

You can build your own jobject from scratch by creating a fresh instance of jobject and then pushing (push_back) key-value pairs into it.

A note on booleans

Booleans are handled a bit differently than other data types. Since everything can be cast to a boolean, having an implicit boolean operator meant everything goes to a boolean! Instead, jvalue objects of type jbool are created using the jvalue::jbool(const bool) static method. If you do not use this method and instead directly create/assign a boolean to a jvalue object, then the boolean will be cast to a jnumber type with a value of 0 or 1.

Key-value pairs

A key-value pair is just that: a key and a value; the members key and value of json::key_value_pair are public. The key member is simply the string of the key whie the value member is a jvalue instance. A jvalue instance can be casted to int, long, double, float, std::string, and json::jarray depending on the type of value it holds.

You can check the type of value by calling get_type() on the value.

You can deserialze a nested object by calling json::jobject::parse(parent.get_entry("child").value).

Arrays

Simpleson includes a class called jarray, which is an extension of a vector of strings. You can create an instance of jarray by parsing a string via json::jarray::parse(input). An instance of jarray can also be casted to std::vector<int>, std::vector<long>, std::vector<double>, and std::vector<float>.

TomMladenov/simpleson