CopyJson

This method extracts a JSON object from a key and stores it in a variable of data type STRING. This STRING can have any length. The method returns the length of the copied JSON object (including null termination). If the destination buffer is too small, it is emptied by a null termination and returned as length 0.

Syntax

METHOD CopyJson : UDINT
VAR_INPUT
  v    : SJsonValue;
END_VAR
VAR_IN_OUT CONSTANT
  pDoc : STRING;
  nDoc : UDINT;
END_VAR

Return value

Inputs

/ Inputs/Outputs

Sample call:

The following JSON document is to be loaded into the DOM memory:

sMessage := ' {"serialNumber":"123","meta":{"batteryVoltage":"1547mV","clickType":"SINGLE"}}';

The value of the JSON object "meta" is to be extracted and stored in a variable of data type STRING. First the JSON document is searched iteratively for the property "meta", then its value or sub-object is extracted by calling the method CopyJson().

jsonDoc         := fbJson.ParseDocument(sMessage);
jsonIterator    := fbJson.MemberBegin(jsonDoc);
jsonIteratorEnd := fbJson.MemberEnd(jsonDoc);
WHILE jsonIterator <> jsonIteratorEnd DO
  sName         := fbJson.GetMemberName(jsonIterator);
  jsonValue     := fbJson.GetMemberValue(jsonIterator);
  IF sName = 'meta' THEN
    fbJson.CopyJson(jsonValue, sString, SIZEOF(sString));
  END_IF
  jsonIterator  := fbJson.NextMember(jsonIterator);
END_WHILE

After this run, the sString variable has the following content:

{"batteryVoltage":"1547mV","clickType":"SINGLE"}