VB代码 If Len(C) <= 2 Then C = "00" & C 后面缺少end if吗?
时间: 2024-03-06 13:49:41 浏览: 34
是的,如果在VB代码中使用If语句,必须使用`End If`来标记结束,否则代码将无法编译通过并提示语法错误。因此,正确的代码应该是:
```VB
If Len(C) <= 2 Then
C = "00" & C
End If
```
在这个示例中,如果字符串变量`C`的长度小于或等于2,则将其前面添加两个0。注意,这里的if语句包含在`Then`和`End If`之间,以标识其开始和结束位置。
相关问题
vb中if判断值是否为空
在VB中,可以使用以下方法判断一个值是否为空:
1. 使用Is关键字:
```
If value Is Nothing Then
'value为空
End If
```
2. 使用Len函数:
```
If Len(value) = 0 Then
'value为空
End If
```
3. 使用IsNull函数:
```
If IsNull(value) Then
'value为空
End If
```
其中,第一种方法适用于对象类型的值,第二种方法适用于字符串类型的值,第三种方法适用于数据库中的值。
vb6 json解析器代码
以下是 VB6 中解析 JSON 字符串的示例代码:
```VB
Option Explicit
Private Type JsonElement
Key As String
Value As Variant
End Type
Private Function ParseJson(ByVal json As String) As Collection
Dim elements As New Collection
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = 1
Do While i <= jsonLen
Dim c As String
c = Mid(json, i, 1)
If c = "{" Then ' Object
Dim obj As New Collection
i = ParseObject(json, i + 1, obj)
elements.Add obj
ElseIf c = "[" Then ' Array
Dim arr As New Collection
i = ParseArray(json, i + 1, arr)
elements.Add arr
ElseIf c = """" Then ' String
Dim value As String
i = ParseString(json, i + 1, value)
elements.Add value
ElseIf c Like "[0-9-]" Then ' Number
Dim value As Variant
i = ParseNumber(json, i, value)
elements.Add value
ElseIf c = "t" Or c = "f" Then ' Boolean
Dim value As Variant
i = ParseBoolean(json, i, value)
elements.Add value
ElseIf c = "n" Then ' Null
Dim value As Variant
i = ParseNull(json, i, value)
elements.Add value
End If
i = i + 1
Loop
Set ParseJson = elements
End Function
Private Function ParseObject(ByVal json As String, ByVal startIndex As Long, ByRef obj As Collection) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
Do While i <= jsonLen
Dim c As String
c = Mid(json, i, 1)
If c = "}" Then ' End of object
Exit Do
If c = """" Then ' Key
Dim key As String
i = ParseString(json, i + 1, key)
i = SkipWhitespace(json, i)
If Mid(json, i, 1) <> ":" Then
Err.Raise 1001, , "Invalid JSON format: expected colon after object key"
End If
i = SkipWhitespace(json, i + 1)
Dim value As Variant
If Mid(json, i, 1) = "{" Then ' Object
Dim childObj As New Collection
i = ParseObject(json, i + 1, childObj)
value = childObj
ElseIf Mid(json, i, 1) = "[" Then ' Array
Dim arr As New Collection
i = ParseArray(json, i + 1, arr)
value = arr
ElseIf Mid(json, i, 1) = """" Then ' String
i = ParseString(json, i + 1, value)
ElseIf Mid(json, i, 1) Like "[0-9-]" Then ' Number
i = ParseNumber(json, i, value)
ElseIf Mid(json, i, 1) = "t" Or Mid(json, i, 1) = "f" Then ' Boolean
i = ParseBoolean(json, i, value)
ElseIf Mid(json, i, 1) = "n" Then ' Null
i = ParseNull(json, i, value)
End If
obj.Add value, key
End If
i = i + 1
Loop
ParseObject = i
End Function
Private Function ParseArray(ByVal json As String, ByVal startIndex As Long, ByRef arr As Collection) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
Do While i <= jsonLen
Dim c As String
c = Mid(json, i, 1)
If c = "]" Then ' End of array
Exit Do
Dim value As Variant
If c = "{" Then ' Object
Dim childObj As New Collection
i = ParseObject(json, i + 1, childObj)
value = childObj
ElseIf c = "[" Then ' Array
Dim childArr As New Collection
i = ParseArray(json, i + 1, childArr)
value = childArr
ElseIf c = """" Then ' String
i = ParseString(json, i + 1, value)
ElseIf c Like "[0-9-]" Then ' Number
i = ParseNumber(json, i, value)
ElseIf c = "t" Or c = "f" Then ' Boolean
i = ParseBoolean(json, i, value)
ElseIf c = "n" Then ' Null
i = ParseNull(json, i, value)
End If
arr.Add value
i = SkipWhitespace(json, i)
If Mid(json, i, 1) = "," Then
i = i + 1
ElseIf Mid(json, i, 1) <> "]" Then
Err.Raise 1002, , "Invalid JSON format: expected comma or end of array"
End If
Loop
ParseArray = i
End Function
Private Function ParseString(ByVal json As String, ByVal startIndex As Long, ByRef value As String) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
Do While i <= jsonLen
Dim c As String
c = Mid(json, i, 1)
If c = """" Then ' End of string
Exit Do
If c = "\" Then ' Escape sequence
Dim nextChar As String
nextChar = Mid(json, i + 1, 1)
If nextChar = """" Then
value = value & """"
i = i + 1
ElseIf nextChar = "\" Then
value = value & "\"
i = i + 1
ElseIf nextChar = "/" Then
value = value & "/"
i = i + 1
ElseIf nextChar = "b" Then
value = value & vbBack
i = i + 1
ElseIf nextChar = "f" Then
value = value & vbFormFeed
i = i + 1
ElseIf nextChar = "n" Then
value = value & vbNewLine
i = i + 1
ElseIf nextChar = "r" Then
value = value & vbCr
i = i + 1
ElseIf nextChar = "t" Then
value = value & vbTab
i = i + 1
ElseIf nextChar = "u" Then
Dim hexCode As String
hexCode = Mid(json, i + 2, 4)
value = value & ChrW("&H" & hexCode)
i = i + 5
Else
Err.Raise 1003, , "Invalid JSON format: unknown escape sequence"
End If
Else
value = value & c
End If
i = i + 1
Loop
ParseString = i
End Function
Private Function ParseNumber(ByVal json As String, ByVal startIndex As Long, ByRef value As Variant) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
Do While i <= jsonLen
Dim c As String
c = Mid(json, i, 1)
If c Like "[0-9-+eE.]" Then
value = value & c
ElseIf c Like "[ },\]]" Then ' End of number
Exit Do
Else
Err.Raise 1004, , "Invalid JSON format: unexpected character in number"
End If
i = i + 1
Loop
value = CDbl(value)
ParseNumber = i - 1
End Function
Private Function ParseBoolean(ByVal json As String, ByVal startIndex As Long, ByRef value As Variant) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
If Mid(json, i, 4) = "true" Then
value = True
ParseBoolean = i + 3
ElseIf Mid(json, i, 5) = "false" Then
value = False
ParseBoolean = i + 4
Else
Err.Raise 1005, , "Invalid JSON format: expected boolean"
End If
End Function
Private Function ParseNull(ByVal json As String, ByVal startIndex As Long, ByRef value As Variant) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
If Mid(json, i, 4) = "null" Then
value = Null
ParseNull = i + 3
Else
Err.Raise 1006, , "Invalid JSON format: expected null"
End If
End Function
Private Function SkipWhitespace(ByVal json As String, ByVal startIndex As Long) As Long
Dim jsonLen As Long
Dim i As Long
jsonLen = Len(json)
i = startIndex
Do While i <= jsonLen And Mid(json, i, 1) Like "[ ]"
i = i + 1
Loop
SkipWhitespace = i
End Function
```
使用示例:
```VB
Dim json As String
json = "{""name"":""John"",""age"":30,""city"":""New York"",""pets"":[""dog"",""cat""]}"
Dim elements As Collection
Set elements = ParseJson(json)
Debug.Print elements("name") ' Output: John
Debug.Print elements("age") ' Output: 30
Debug.Print elements("city") ' Output: New York
Debug.Print elements("pets")(1) ' Output: cat
```
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