#JSONLib for C++ 2.1

JSONLib is a dynamic library for c++ which allows parse,read and build data with JSON format, using ECMAC-404 standar for JSON, and can read file with UTF-8 or UTF-16 content.

The repository has 2 projects

• src is the main project and it contains the source code and distribution file for JSONLib.
• Sample project has a sample to use the JSONLib. #Using JSONLib

##prerequisites

This code was developed with:

• Visual Studio Code
• gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
• PlugIn C/C++ for Visual Studio Code
• C++17.
• GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2

Building

Compiling

Build all

$make

Build Sample

$make sample

Cleaning

$make clean

Install / Uninstall

$sudo make install

$sudo make uninstall

If you want use it library with another OS just recompile the library.

Include Header file JSONLib.h (JSONLib/include/) and link with the library file libJSONLib.so (usr/lib/).

#How to use

##Select UTF-8 or UTF-16

To work with UTF-8 you must use the namespace json::utf8:

using namespace json::utf8;

To work with UTF-16 you must use the namespace json::wide:

using namespace json::wide;

for this mode (UTF-16) the library use wstring and, for this reason, all the strings must be handled as UTF-16: L"My Wide String".

No matter what kind of codec was choosed, there is a names pace that must be added to handled the JSONObect: json::common, wich has the definitions of JSONType that could has every JSONObject and error definitions (Codes and Descriptions).

using namespace json::common;

##Load and parse a JSON File or JSON String

JSONLib can read and parse a file with JSON content, in UTF-8 or UTF-16.

To load a file just the method JSONObject::loadJSONByFile, as this sample shows:

    JSONObject obj;

    string jsonFile = "../utf-8.json";
    pair<int,string> res = obj.loadJSONByFile(jsonFile);

    if(res.first == ERR_C_OK)
    {
        cout << "JSON OUTPUT:" << endl << "("<< obj.toString() << ")." << endl;


        print(1,obj,-1);
    }
    else
    {
        cout << "JSON ERROR: Code ("<< res.first << "): [" << res.second << "]" << endl;
        return false;
    }

    cout << endl << endl;
    return true;

loadJSONByFile load and parse the file and the content is stored into the JSONObject instance.

When it use the JSONLib with UTF-16 the method loadJSONByFile use a std::string to set the path file.

To load a JSON string and parse it, use the method JSONObject::loadJSON, as this sample shows:

    JSONObject obj;

    pair<int,string> res = obj.loadJSON(json_txt);

As JSONObject::loadJSONByFile does, it loads, parses and stores the JSON content into the the JSONObject instance.

If there is a problema with loading and parsing the JSON Content, both methods return a pair<int,string> which has the error code and error description of the problem:

pair<int,string> res = obj.loadJSON(json_txt);

	if(res.first == ERR_C_OK)
	{
    //...
	}
	else
	{
		cout << "JSON ERROR: Code ("<< res.first << "): [" << res.second << "]" << endl;
		return false;
	}

Reading and modify the JSONLib content

After loading and parse the content of a file or string, JSON content is stored into the instance of JSONObject. The JSONObject can store another JSONObject that can represent, according with JSON Standar:

• NULL (Empty) value
• Boolean value.
• Number Value.
• String value.
• Object, which is a value and can store another objects, values or arrays.
• Array, which has a collection of values

All the types are defined in the enum json::common::JSONType.

To read a value, which has a defined key, use the operator [] and the key of the value:

JSON Content:

{
  "Null Value": null,
  "Boolean Value": true,
  "Integer Number": 12,
  "Double Number": 231.45,
  "Double Number Exp": -443.32,
  "String Value": "My String"
}

Reading the value with key Integer Number:

JSONObject obj;

//Parse the JSON content

//Reading the value
cout << "\tInteger Number     = [" << obj["Integer Number"].toString(false) << "]" << endl;

To get the type of the JSONObject (Object, Array or Value), use the method type() which return a value of type json::common::JSONType:

if(val.type() == JSONType::EMPTY)
//...
else if(val.type() == JSONType::Boolean)
//...
else if(val.type() == JSONType::Array)

To modify a value or add a new value into the JSONObject use the operator =, as it shows:

obj["Integer Number"] = 666;

The JSONObject detect the type of value using its override operators:

void operator=(int);
void operator=(long);
void operator=(float);
void operator=(double);

To access at inner Object use the operator [] to navigate across the inner objects and value:

JSON Content with array:

{
  "glossary": {
    "title": "example glossary",
    "GlossDiv": {
      "title": "S",
      "GlossList": {
        "GlossEntry": {
          "ID": "SGML",
          "SortAs": "SGML",
          "GlossTerm": "Standard Generalized Markup Language",
          "Acronym": "SGML",
          "Abbrev": "ISO 8879:1986",
          "GlossDef": {
            "para": "A meta-markup language, used to create markup languages such as DocBook.",
            "GlossSeeAlso": [
              "GML",
              "XML"
            ]
          },
          "GlossSee": "markup"
        }
      }
    }
  }
}

//Getting an inner JSONObject.
JSONObject innerObj = obj["glossary"]["GlossDiv"]["GlossList"]["GlossEntry"]["GlossDef"];

//Use the inner JSONObject and navigate across its values.
cout << "GlossSeeAlso Para:" << innerObj["para"].toString() << endl;

To navigate across an array use the operator [] and set the index, which is base 0:

cout << "GlossSeeAlso Ittem 1:" << innerObj["GlossSeeAlso"][0].toString() << endl;
cout << "GlossSeeAlso Ittem 2:" << innerObj["GlossSeeAlso"][1].toString() << endl;

To add a new JSONObject into the Array or Object use the operator +=:

JSONObect obj; //The main JSONObject

//load and parse...

JSONObject innerObj = obj["glossary"]["GlossDiv"]["GlossList"]["GlossEntry"]["GlossDef"];

JSONObject nItem;
nItem = string("My New Item");
innerObj["GlossSeeAlso"]+= nItem; //Adding a new Object to array.
cout << "GlossSeeAlso Ittem 3:" << innerObj["GlossSeeAlso"][2].toString() << endl;

Use of memory

The JSONLib doesn't use dynamic memory. Instead of it, JSONLib use copyable object. So, avoid alloc dynamic memory for each instance of JSONObject.

So, avoid create any instance of JSONObject as this:

JSONObect* obj = new JSONObect();

If you need send an instance of JSONObject as argument and manipulate it, send it by reference:

void printJson(int level, JSONObject& val, int index)
{
  cout.width(level*2);
	cout << " ";
  if(val.type() == JSONType::EMPTY)
    //...
}

int main(int argc, char **argv) {
{
    string json_txt;

    cout << "Reading file: " << jsonFile << endl;

    JSONObject obj;

    pair<int,string> res = obj.loadJSONByFile(jsonFile);

    if(res.first == ERR_C_OK)
    {
        printJson(1,obj,-1); //Sending a reference of JSONObjet.
    }
}