common_types.md

Common data types

Overview

jsonpp doesn't enforce the data types when parsing or dumping JSON document. For example, short int, unsigned int, or other integral types can be used as JSON integers, std::vector<std::string>, std::list<int>, or other sequence containers, can be used as JSON array.

When parsing JSON without specifying the prototype argument, the parser will use default data types to store the JSON data. This document discusses the default data types.

Header

#include "jsonpp/common.h"

Default data types

using JsonNull = void *;
using JsonBool = bool;
using JsonInt = int64_t;
using JsonUnsignedInt = uint64_t;
using JsonReal = double;
using JsonString = std::string;
using JsonArray = std::vector<metapp::Variant>;
using JsonObject = std::map<std::string, metapp::Variant>;

JsonNull represents null.
JsonBool represents JSON boolean type, true and false.
JsonInt represents JSON integral type. The integer can be negative, zero, or positive.
JsonUnsignedInt represents unsigned integer. Not all parser backends support it. Currently only simdjson supports it. Usually an integer is parsed as unsigned if it's positive and larger than the maximum value of integer.
JsonReal represents JSON float point number.
JsonString represents JSON string.
JsonArray represents JSON array. It's heterogeneous data structure, the element type is metapp::Variant, so any data types can be stored.
JsonObject represents JSON object. It's heterogeneous data structure, the mapped value type is metapp::Variant, so any data types can be stored.

Type constants

There are enum values to identify the types. jtNone means it's not any known default data type.

enum class JsonType {
  jtNone,
  jtNull,
  jtBool,
  jtInt,
  jtUnsignedInt,
  jtReal,
  jtString,
  jtArray,
  jtObject
};

Function getJsonType

JsonType getJsonType(const metapp::Variant & var);

Returns the data type of var if it holds any default data type, otherwise returns JsonType::jtNone.