C++

Using Pre-defined JSON Templates

See more JSON Examples

Demonstrates how to predefine a JSON template, and then use it to emit JSON with variable substitutions.

Note: This example requires Chilkat v9.5.0.67 or greater.

C++

#include <CkJsonObject.h>
#include <CkHashtable.h>

void ChilkatSample(void)
    {
    // One way to create JSON is to do it in a straightforward manner:
    CkJsonObject json;
    json.put_EmitCompact(false);
    json.UpdateString("id","0001");
    json.UpdateString("type","donut");
    json.UpdateString("name","Cake");
    json.UpdateString("image.url","images/0001.jpg");
    json.UpdateInt("image.width",200);
    json.UpdateInt("image.height",200);
    json.UpdateString("thumbnail.url","images/thumbnails/0001.jpg");
    json.UpdateInt("thumbnail.width",32);
    json.UpdateInt("thumbnail.height",32);
    std::cout << json.emit() << "\r\n";

    // The JSON created by the above code:

    // 	{ 
    // 	  "id": "0001",
    // 	  "type": "donut",
    // 	  "name": "Cake",
    // 	  "image": { 
    // 	    "url": "images/0001.jpg",
    // 	    "width": 200,
    // 	    "height": 200
    // 	  },
    // 	  "thumbnail": { 
    // 	    "url": "images/thumbnails/0001.jpg",
    // 	    "width": 32,
    // 	    "height": 32
    // 	  }
    // 	}

    // An alternative is to predefine a template, and then use it to emit with variable substitutions.
    // For example:

    CkJsonObject jsonTemplate;
    jsonTemplate.UpdateString("id","{$id}");
    jsonTemplate.UpdateString("type","donut");
    jsonTemplate.UpdateString("name","{$name}");
    jsonTemplate.UpdateString("image.url","{$imageUrl}");
    // The "i." indicates that it's an integer variable.
    jsonTemplate.UpdateString("image.width","{$i.imageWidth}");
    jsonTemplate.UpdateString("image.height","{$i.imageHeight}");
    jsonTemplate.UpdateString("thumbnail.url","{$thumbUrl}");
    jsonTemplate.UpdateString("thumbnail.width","{$i.thumbWidth}");
    jsonTemplate.UpdateString("thumbnail.height","{$i.thumbHeight}");
    // Give this template a name.
    jsonTemplate.Predefine("donut");

    // --------------------------------------------------------------------------
    // OK, the template is defined.  Defining a template can be done once
    // at the start of your program, and you can discard the jsonTemplate object (it
    // doesn't need to stick around..)

    // Now we can create instances of the JSON object by name:
    CkJsonObject jsonDonut;
    jsonDonut.put_EmitCompact(false);
    jsonDonut.LoadPredefined("donut");
    std::cout << jsonDonut.emit() << "\r\n";

    // The output is this:

    // 	{ 
    // 	  "id": "{$id}",
    // 	  "type": "donut",
    // 	  "name": "{$name}",
    // 	  "image": { 
    // 	    "url": "{$imageUrl}",
    // 	    "width": "{$i.imageWidth}",
    // 	    "height": "{$i.imageHeight}"
    // 	  },
    // 	  "thumbnail": { 
    // 	    "url": "{$thumbUrl}",
    // 	    "width": "{$i.thumbWidth}",
    // 	    "height": "{$i.thumbHeight}"
    // 	  }
    // 	}

    // Finally, we can substitute variables like this:
    CkHashtable donutValues;
    donutValues.AddStr("id","0001");
    donutValues.AddStr("name","Cake");
    donutValues.AddStr("imageUrl","images/0001.jpg");
    donutValues.AddInt("imageWidth",200);
    donutValues.AddInt("imageHeight",200);
    donutValues.AddStr("thumbUrl","images/thumbnails/0001.jpg");
    donutValues.AddInt("thumbWidth",32);
    donutValues.AddInt("thumbHeight",32);

    // Emit with variable substitutions:
    bool omitEmpty = true;
    std::cout << jsonDonut.emitWithSubs(donutValues,omitEmpty) << "\r\n";

    // Output:

    // 	{ 
    // 	  "id": "0001",
    // 	  "type": "donut",
    // 	  "name": "Cake",
    // 	  "image": { 
    // 	    "url": "images/0001.jpg",
    // 	    "width": 200,
    // 	    "height": 200
    // 	  },
    // 	  "thumbnail": { 
    // 	    "url": "images/thumbnails/0001.jpg",
    // 	    "width": 32,
    // 	    "height": 32
    // 	  }
    // 	}

    // Change some of the values:
    donutValues.AddStr("id","0002");
    donutValues.AddStr("imageUrl","images/0002.jpg");
    donutValues.AddStr("thumbUrl","images/thumbnails/0002.jpg");

    std::cout << jsonDonut.emitWithSubs(donutValues,omitEmpty) << "\r\n";

    // Output:

    // 	{ 
    // 	  "id": "0002",
    // 	  "type": "donut",
    // 	  "name": "Cake",
    // 	  "image": { 
    // 	    "url": "images/0002.jpg",
    // 	    "width": 200,
    // 	    "height": 200
    // 	  },
    // 	  "thumbnail": { 
    // 	    "url": "images/thumbnails/0002.jpg",
    // 	    "width": 32,
    // 	    "height": 32
    // 	  }
    // 	}
    }