cJson Frequently Asked Questions (FAQ)

Basic Questions

Q1: Where is the cJson class defined?

A: The cJson class is defined in the VBMAN library, located at:

vbman/src/Tools/Json/cJson.cls

To use it in your project, add a reference to the VBMAN library:

'Standard reference method
Dim Json As New VBMANLIB.cJson

'Or use the VBMAN global instance
With VBMAN.Json
    '...
End With

Q2: Why do array indices start from 1 instead of 0?

A: cJson internally uses VB's Collection object to store arrays, and VB's Collection indexing starts from 1. This follows VB developer conventions.

'Add elements using 0 (means append)
Json.Items(0) = "Element 1"
Json.Items(0) = "Element 2"

'Access using 1-based index (via Root)
MsgBox Json.Root("items")(1)  'Element 1
MsgBox Json.Root("items")(2)  'Element 2

Q3: How to clear a cJson instance?

A: Use the Clear method:

Json.Clear  'Clear all data

Note: When using the VBMAN.Json global instance, it's recommended to call Clear first:

With VBMAN.Json
    .Clear  'Clean previous data
    .Item("key") = "value"
End With

Usage Questions

Q4: How to check if JSON parsing was successful?

A: Use the LastSuccess property:

Json.Decode JsonText
If Json.LastSuccess Then
    MsgBox "Parse successful"
Else
    MsgBox "Parse failed: " & Json.LastError
End If

Q5: How to check if a key exists?

A: Use the RootItem.Exists method to check, use Root to access:

If Json.RootItem.Exists("key") Then
    MsgBox Json.Root("key")
Else
    MsgBox "Key does not exist"
End If

Q6: How to iterate through a JSON array?

A: Use Root to access the array, two iteration methods:

'Method 1: For Each (recommended)
Dim Item As Variant
For Each Item In Json.Root("data")
    Debug.Print Item("name")
Next

'Method 2: For loop (index starts from 1)
Dim i As Long
For i = 1 To Json.Root("data").Count
    Debug.Print Json.Root("data")(i)("name")
Next

Q7: How to handle nested objects?

A: Use Root for chained access or layered access:

'Chained access (recommended)
MsgBox Json.Root("level1")("level2")("level3")

'Or use default member feature (more concise)
MsgBox Json("level1")("level2")("level3")

'Layered access (recommended for deep nesting)
Dim Level1 As Object
Dim Level2 As Object
Set Level1 = Json.Root("level1")
Set Level2 = Level1("level2")
MsgBox Level2("level3")

Encoding Issues

Q8: How to display Chinese characters instead of Unicode?

A: Set the third parameter of Encode to True:

Json.Encode(, 2, True)  'Third parameter True means display Chinese as-is

Q9: How to format JSON string output?

A: Set the second parameter of Encode:

Json.Encode(, 2)     'Use 2-space indent
Json.Encode(, 4)     'Use 4-space indent
Json.Encode(, vbTab) 'Use Tab indent

Q10: How to handle special characters?

A: cJson automatically handles special character escaping:

Json.Item("text") = "Text with \"quotes\" and \\backslashes"
'Output: "text": "Text with \"quotes\" and \\backslashes"

File Operation Questions

Q11: How to load JSON from a file?

A: Use the LoadFrom method:

'Standard method
With New cJson
    .LoadFrom "C:\data.json"
    MsgBox .Item("name")
End With

'Chained calling
MsgBox VBMAN.Json.LoadFrom("C:\data.json")("name")

Q12: How to save JSON to a file?

A: Use the SaveTo method:

Json.SaveTo "C:\data.json"                    'Simple save
Json.SaveTo "C:\data.json", "UTF-8"          'Specify encoding
Json.SaveTo "C:\data.json", "UTF-8", 2, True 'Formatted and display Chinese

Q13: What character encodings are supported?

A: Common character encodings are supported:

• UTF-8 (recommended)
• UTF-16
• GB2312
• GBK
• ASCII

HTTP Related Questions

Q14: How to send JSON data?

A: Construct a JSON string and send it:

'Construct request body
Dim Body As String
With New cJson
    .Item("key") = "value"
    Body = .Encode()
End With

'Send POST request
With New cHttpClient
    .SetRequestContentType JsonString
    .SendPost "https://api.example.com", Body
End With

Q15: How to parse JSON returned by an API?

A: Use the ReturnJson method:

With VBMAN.HttpClient.Fetch(ReqGet, "https://api.example.com").ReturnJson()
    'Formatted display
    Text1.Text = .Encode(, 2, True)

    'Extract data
    If .Item("code") = 200 Then
        MsgBox .Item("data")("name")
    End If
End With

Q16: How to handle JSONP format?

A: cJson's Decode method automatically handles JSONP format:

'The following formats can all be auto-parsed
Json.Decode "callback({""name"":""John""});"
Json.Decode "var data = {""name"":""John""};"
Json.Decode "{""name"":""John""}"  'Standard JSON

Error Handling

Q17: What are common errors?

A: Common errors and solutions:

Error	Cause	Solution
Index out of bounds	Accessing non-existent array index	Check array length before access
Key not found	Accessing non-existent key	Use Exists method to check
Type mismatch	Data type doesn't match variable	Use type conversion functions
Parse failure	Invalid JSON format	Check input string format

Q18: How to debug JSON issues?

A: Use these debugging techniques:

'1. Formatted output to view structure
Debug.Print Json.Encode(, 2, True)

'2. Check error information
Json.Decode BadJsonText
If Not Json.LastSuccess Then
    Debug.Print "Error: " & Json.LastError
End If

'3. Check data type
Debug.Print TypeName(Json.Item("field"))

Performance Questions

Q19: Tips for handling large data volumes?

A:

1. Use compact format for transmission: Json.Encode() (no formatting)
2. Avoid deep nested object lookups
3. Release unused objects promptly
4. Consider batch processing for large data volumes

Q20: What's the difference between global and new instances?

A:

Feature	VBMAN.Json (Global)	New cJson (New Instance)
Lifecycle	Application lifetime	Released with code block end
Data Sharing	Globally shared	Independent isolation
Use Case	Cache global config	Temporary data processing
Note	Need manual Clear	Auto cleanup

Advanced Questions

Q21: How to construct JSON with array root node?

A: First call NewItem or NewItems:

With New cJson
    'Root is an array
    With .NewItem()
        .Item("name") = "John"
    End With
    With .NewItem()
        .Item("name") = "Jane"
    End With

    'Result: [{"name": "John"}, {"name": "Jane"}]
    Debug.Print .Encode(, 2, True)
End With

Q22: How to merge two JSON objects?

A: Manually copy key-value pairs:

Private Sub MergeJson(Target As cJson, Source As cJson)
    Dim Key As Variant
    For Each Key In Source.RootItem.Keys
        Target.Item(Key) = Source.Item(Key)
    Next
End Sub

Q23: How to copy a JSON object?

A: Encode then decode:

Dim Copy As New cJson
Copy.Decode Original.Encode()

Q24: What's the difference between Root and Item?

A:

Feature	Root	Item
Default Member	Yes (can use Json("key"))	No
Return Type	Object (Dictionary/Collection)	Variant
Chained Access	Supported	Limited support
Primary Use	Reading data	Setting values
Example	Json.Root("a")("b")	Json.Item("a") = 1

Recommended Usage:

'Set values with Item
Json.Item("name") = "John"

'Read values with Root
MsgBox Json.Root("name")
MsgBox Json.Root("address")("city")  'Chained access to nested object

'Shorthand form (using Root as default member)
MsgBox Json("name")
MsgBox Json("address")("city")

Q25: How to handle date types?

A: Dates are converted to strings; it's recommended to format them:

Json.Item("created") = Format(Now(), "yyyy-mm-dd HH:mm:ss")