How to convert JSON file to a WSTRING?

I want to use WebClient Function Block from Web_Client_SL library in IIOT to PUT an APPLICATION_JSON. For this goal I need to define the PostValue as a WSTRING and then define a Pointer for it to give the pointer as an input to FB. The first problem which I have is that when I give a json file to a WSTRING variable, the compiler returns an error. So what is the proper way to assign this json string in a variable?

For solving this problem, I used the JSON_Utilities_SL library in IIOT to convert a JSON file to a WSTRING. With JSONFileReader FB, I can make a JSONData object. How we can convert this JSONData object to WSTRING?

There is a function called JSONElementToString. For implementing it we need to extract the JSON elements. So I used the GetElementByIndex method to get the JSON elements. But the problem is that, I do not know the number of indexes for an arbitrary JSON file. What should I do?

I'm not sure, if I understand your description correct. I see 2 differnet use cases:

A: Pass the JSON file content, without changing anything

Open file, Read content STRING/WSTRING, Close file
Send WSTRING via Web_Client_SL library

B: Pass the JSON file content, with changing it

Open file, Read content STRING/WSTRING, Close file
Parse string into JSON object
Edit JSON object
Create WSTRING from JSON object
Send WSTRING via Web_Client_SL library

Remarks:

When you do not have to change the content of the JSON object, you do not need the JSON library of CoDeSys.
Just use the library CXA_FileAsync. It's a wrapper around the CoDeSys function, which are really hard to use.
If the file format is STRING, you have to read it as STRING and convert it afterwards to WSTRING
If the file format is WSTRING, you have to read it as WSTRING
In my tests around 1 year ago, the CoDeSys JSON library was not very stable. I would use it only for very basic stuff but not for complex JSON's.