Lua

Get the Index of a JSON Member

See more JSON Examples

This example demonstrates how to get the index of a given member by name.

{
  "name": "donut",
  "image":
    {
    "fname": "donut.jpg",
    "w": 200,
    "h": 200
    },
  "thumbnail":
    {
    "fname": "donutThumb.jpg",
    "w": 32,
    "h": 32
    }
}

Lua

local chilkat = require("chilkat")

local json = chilkat.JsonObject.new()

-- This is the above JSON with whitespace chars removed (SPACE, TAB, CR, and LF chars).
-- The presence of whitespace chars for pretty-printing makes no difference to the Load
-- method.
local jsonStr = "{\"name\": \"donut\",\"image\":{\"fname\": \"donut.jpg\",\"w\": 200,\"h\": 200},\"thumbnail\":{\"fname\": \"donutThumb.jpg\",\"w\": 32,\"h\": 32}}"

local success = json:load(jsonStr)
if not success then
    print(json.last_error_text)
    return
end

-- The top-level JSON object has three members: name, image, and thumbnail.
local nameIndex = json:index_of("name")
-- The index of the "name" member is 0.
print("nameIndex = " .. nameIndex)

local thumbIndex = json:index_of("thumbnail")
-- The index of the "thumbnail" member is 2.
print("thumbIndex = " .. thumbIndex)

-- The "fname" member is NOT a direct member of the top-level JSON object.
-- It is a member of a nested object.  If we try to get the index of this
-- member using the top-level JSON object, it is not found (and returns -1).
local fnameIndex = json:index_of("fname")
-- The fnameIndex is -1 (not found).  This is correct.
print("fnameIndex = " .. fnameIndex)

-- Get the "image" object.
local imageObj = chilkat.JsonObject.new()
json:object_of2("image", imageObj)

-- Now we can get the index of the "fname" object, because it is a direct
-- member of the "image" object:
fnameIndex = imageObj:index_of("fname")
print("fnameIndex = " .. fnameIndex)