Question

我正在尝试设计简单的编译器（扫描仪），我需要知道如何编写代码识别标识符包含字母和数字，例如id45并打印

Answer 1

如果你想检查一个字符串是否以字母开头，并且之后可能包含字母或数字，你可以使用常规表达式，而不知道你想要什么。

Function IsVar(txt as string) as Boolean
  'txt ="id45"

IsVar = False

Dim re1 As String
re1 ="((?:[a-z][a-z0-9_]*))"

Dim r As New RegExp
  r.Pattern = re1
  r.IgnoreCase = True

  bX = re.Test(sSendLine)
  If bX = True Then
IsVar = True
  End If

End Function

基本上常规指令“说”

[a-z] match a single character present in the list
   a-z a single character in the range between a and z (case sensitive)
[a-z0-9_]* match a single character present in the list
   a-z a single character in the range between a and z (case sensitive)
   0-9 or a single character in the range between 0 and 9
   _   or the character _ (underscore)
* do the previous match from zero to unlimited times (as many times as possible) [greedy]

如果我们应该有一个字符串“id45”。

the first character is an I -- first instruction successful (next)
character 2 = d             -- second instruction successful (repeat)
character 3 = 4             -- second instruction successful (repeat)
character 4 = 5             -- second instruction successful (repeat)
no more characters          -- return true

如果你不想要和下划线，只需在正则表达式中取出下划线。

希望这会有所帮助查理

code vb6.0识别标识符包含字母和数字

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