如何确定字符串是否是有效的变量名？

Question

我正在寻找一种快速方式（在C＃中）来确定字符串是否是有效的变量名。我的第一个直觉是鞭打一些正则表达式，但我想知道是否有更好的方法来做到这一点。就像某种秘密方法隐藏在一个名为IsThisAValidVariableName（字符串名称）的地方，或者其他一些光滑的方法，这样做不容易因为缺乏正则表达式而产生的错误。

Answer 1

试试这个：

// using System.CodeDom.Compiler;
CodeDomProvider provider = CodeDomProvider.CreateProvider("C#");
if (provider.IsValidIdentifier (YOUR_VARIABLE_NAME)) {
      // Valid
} else {
      // Not valid
}

Answer 2

  public static bool IsIdentifier(string text)
  {
     if (string.IsNullOrEmpty(text))
        return false;
     if (!char.IsLetter(text[0]) && text[0] != '_')
        return false;
     for (int ix = 1; ix < text.Length; ++ix)
        if (!char.IsLetterOrDigit(text[ix]) && text[ix] != '_')
           return false;
     return true;
  }

Answer 3

@字符周围有一些特殊情况很容易忘记检查 - 即'@'本身不是有效的标识符，"@1foo"也不是。{1}}。要捕获这些字符串，您可以先检查字符串是否为关键字，然后从字符串的开头删除@，然后检查剩下的字符是否为有效标识符（不允许@字符）。

这里我将它与一个解析标识符中的Unicode转义序列的方法相结合，并希望完成C＃（5.0）Unicode字符检查。要使用它，首先调用TryParseRawIdentifier()来处理关键字，转义序列，格式化字符（被删除）和逐字标识符。接下来，将结果传递给IsValidParsedIdentifier()以检查第一个和后续字符是否有效。请注意，当且仅当C＃认为标识符相同时，从TryParseRawIdentifier()返回的字符串才相等。

public static class CSharpIdentifiers
{
    private static HashSet<string> _keywords = new HashSet<string> {
        "abstract", "as", "base", "bool", "break", "byte", "case", "catch", "char", "checked",
        "class", "const", "continue", "decimal", "default", "delegate", "do", "double", "else",
        "enum", "event", "explicit", "extern", "false", "finally", "fixed", "float", "for",
        "foreach", "goto", "if", "implicit", "in", "int", "interface", "internal", "is", "lock",
        "long", "namespace", "new", "null", "object", "operator", "out", "override", "params",
        "private", "protected", "public", "readonly", "ref", "return", "sbyte", "sealed",
        "short", "sizeof", "stackalloc", "static", "string", "struct", "switch", "this", "throw",
        "true", "try", "typeof", "uint", "ulong", "unchecked", "unsafe", "ushort", "using",
        "virtual", "void", "volatile", "while"
    };

    public static IReadOnlyCollection<string> Keywords { get { return _keywords; } }


    public static bool TryParseRawIdentifier(string str, out string parsed)
    {
        if (string.IsNullOrEmpty(str) || _keywords.Contains(str)) { parsed = null; return false; }

        StringBuilder sb = new StringBuilder(str.Length);

        int verbatimCharWidth = str[0] == '@' ? 1 : 0;

        for (int i = verbatimCharWidth; i < str.Length; ) //Manual increment
        {
            char c = str[i];

            if (c == '\\')
            {
                char next = str[i + 1];

                int charCodeLength;
                if (next == 'u') charCodeLength = 4;
                else if (next == 'U') charCodeLength = 8;
                else { parsed = null; return false; }
                //No need to check for escaped backslashes or special sequences like \n,
                //as they not valid identifier characters

                int charCode;
                if (!TryParseHex(str.Substring(i + 2, charCodeLength), out charCode)) { parsed = null; return false; }

                sb.Append(char.ConvertFromUtf32(charCodeLength)); //Handle characters above 2^16 by converting them to a surrogate pair
                i += 2 + charCodeLength;
            }
            else if (char.GetUnicodeCategory(str, i) == UnicodeCategory.Format)
            {
                //Use (string, index) in order to handle surrogate pairs
                //Skip this character
                if (char.IsSurrogatePair(str, i)) i += 2;
                else i += 1;
            }
            else
            {
                sb.Append(c);
                i++;
            }
        }

        parsed = sb.ToString();
        return true;
    }

    private static bool TryParseHex(string str, out int result)
    {
        return int.TryParse(str, NumberStyles.AllowHexSpecifier, CultureInfo.InvariantCulture, out result);
        //NumberStyles.AllowHexSpecifier forces all characters to be hex digits
    }

    public static bool IsValidParsedIdentifier(string str)
    {
        if (string.IsNullOrEmpty(str)) return false;

        if (!IsValidParsedIdentifierStart(str, 0)) return false;

        int firstCharWidth = char.IsSurrogatePair(str, 0) ? 2 : 1;

        for (int i = firstCharWidth; i < str.Length; ) //Manual increment
        {
            if (!IsValidParsedIdentifierPart(str, i)) return false;
            if (char.IsSurrogatePair(str, i)) i += 2;
            else i += 1;
        }

        return true;
    }

    //(String, index) pairs are used instead of chars in order to support surrogate pairs
    //(Unicode code-points above 2^16 represented using two 16-bit characters)

    public static bool IsValidParsedIdentifierStart(string s, int index)
    {
        return s[index] == '_' || char.IsLetter(s, index) || char.GetUnicodeCategory(s, index) == UnicodeCategory.LetterNumber;
    }

    public static bool IsValidParsedIdentifierPart(string s, int index)
    {
        if (s[index] == '_' || (s[index] >= '0' && s[index] <= '9') || char.IsLetter(s, index)) return true;

        switch (char.GetUnicodeCategory(s, index))
        {
            case UnicodeCategory.LetterNumber: //Eg. Special Roman numeral characters (not covered by IsLetter())
            case UnicodeCategory.DecimalDigitNumber: //Includes decimal digits in other cultures
            case UnicodeCategory.ConnectorPunctuation:
            case UnicodeCategory.NonSpacingMark:
            case UnicodeCategory.SpacingCombiningMark:
            //UnicodeCategory.Format handled in TryParseRawIdentifier()
                return true;
            default:
                return false;
        }
    }
}

Answer 4

更长的路，加上它慢得多，就是使用反射来迭代类/命名空间的成员，并通过检查反射的成员**。ToString（）**是否与字符串输入相同来进行比较，这需要预先加载组件。

另一种方法（通过使用已经可用的Antlr扫描程序/解析器克服正则表达式使用的更长的方法）接近解析/删除C＃代码然后扫描成员名称（即变量）和比较用作输入的字符串，例如，输入一个名为'fooBar'的字符串，然后指定源（例如汇编或C＃代码）并通过分析专门查看成员的声明来扫描它，例如

private int fooBar;

是的，它很复杂，但是当你意识到编译器编写者正在做什么时会产生强大的理解，并且会将你对C＃语言的了解提升到一个你对语法及其特性非常熟悉的程度。

Answer 5

在 WPF 中，这可用于检查字符串是否为有效的变量名。但是它不能识别“ public”之类的保留字符串。

// works only in WPF!
public static bool CheckIfStringIsValidVarName(string stringToCheck)
{
    if (string.IsNullOrWhiteSpace(stringToCheck))
        return false;

    TextBox textBox = new TextBox();

    try
    {
        // stringToCheck == ""; // !!! does NOT throw !!!
        // stringToCheck == "Name$"; // throws
        // stringToCheck == "0"; // throws
        // stringToCheck == "name with blank"; // throws
        // stringToCheck == "public"; // does NOT throw
        // stringToCheck == "ValidName";

        textBox.Name = stringToCheck;
    }
    catch (ArgumentException ex)
    {
        return false;
    }

    return true;
}