String.Replace 没有按预期工作

Question

我有一个程序

    public void TestMethod2()
    {
        string[] keywords =
        {
            "SELECT", "FROM", "WHERE", "GROUP", "HAVING", "ORDER", "LEFT",  "RIGHT", "JOIN", "INNER", "OUTER", "ASC",
            "DESC", "AND", "OR","IN", "BETWEEN", "BY", "NOT", "ON", "AS", "CASE", "WHEN", "ELSE", "UPDATE", "SET"
        };

        var actualString = "SELECT * FROm A Join B On C in D case e join t left outer join inner join right join";

        foreach (var text in actualString.Split(' '))
        {
            var isExists = keywords.Any(x => x.Equals(text, StringComparison.OrdinalIgnoreCase));

            if (!isExists)
            {
                continue;
            }

            actualString = actualString.Replace(text, text.ToUpper());
        }


        var expectedString = "SELECT * FROM A JOIN B ON C IN D CASE e JOIN t LEFT OUTER JOIN INNER JOIN RIGHT JOIN";

    }

我是 C# 的新手。我不清楚为什么 Replace() 方法没有按预期工作。它正在显示输出 SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INNER JOIN RIGHT JOIN

有人能告诉我为什么 Replace() 会这样吗？ 提前致谢。

Answer 1

我建议使用Regex.Replace 而不是只使用String.Replace 和

 \bKeyWord\b 

模式 当且仅当它是一个整个单词时，将子字符串视为关键字：

 select horror 
   from torro 
  where corner = 1 
     or ordain = 2

应该变成

 SELECT horror -- even if horror has two "or"
   FROM torro  -- even if torro has two "or"
  WHERE corner = 1 -- even if corner contains "or"
     OR ordain = 2 -- even if ordain contains "or"

实施：

string[] keywords = {
  "SELECT", "FROM", "WHERE", "GROUP", "HAVING", "ORDER", "LEFT",  "RIGHT",
  "JOIN", "INNER", "OUTER", "ASC", "DESC", "AND", "OR","IN", "BETWEEN", 
  "BY", "NOT", "ON", "AS", "CASE", "WHEN", "ELSE", "UPDATE", "SET"
};

var actualString = 
  "SELECT * FROm A Join B On C in D case e join t left outer join inner join right join";

foreach (var keyword in keywords)
  actualString = Regex.Replace(
    actualString,
    @"\b" + Regex.Escape(keyword) + @"\b",
    keyword.ToUpper(),
    RegexOptions.IgnoreCase); 

Answer 2

从这里的答案中得到了一个清晰的想法。最后通过将 foreach 更改为 for 循环来解决这个问题。谢谢你们。

public void TestMethod2()
{
    string[] keywords =
    {
        "SELECT", "FROM", "WHERE", "GROUP", "HAVING", "ORDER", "LEFT",  "RIGHT", "JOIN", "INNER", "OUTER", "ASC",
        "DESC", "AND", "OR","IN", "BETWEEN", "BY", "NOT", "ON", "AS", "CASE", "WHEN", "ELSE", "UPDATE", "SET"
    };

    var actualString = "SELECT * FROm A Join B On C in D case e join t left outer join inner join right join";

    var cnt = sqlTest.Split(' ').Count();
    for (int i = 0; i < cnt; i++)
    {
        var text = sqlTest.Split(' ')[i];
        var isExists = keywords.Any(x => x.Equals(text, StringComparison.OrdinalIgnoreCase));

        if (!isExists)
        {
            continue;
        }

        actualString = actualString.Replace(text, text.ToUpper());
    }


    var expectedString = "SELECT * FROM A JOIN B ON C IN D CASE e JOIN t LEFT OUTER JOIN INNER JOIN RIGHT JOIN";

}

Answer 3

它的行为符合预期。这是一行一行的输出：

[SELECT] -> SELECT * FROm A Join B On C in D case e join t left outer join inner join right join [FROm] -> SELECT * FROM A Join B On C in D case e join t left outer join inner join right join [Join] -> SELECT * FROM A JOIN B On C in D case e join t left outer join inner join right join [On] -> SELECT * FROM A JOIN B ON C in D case e join t left outer join inner join right join [in] -> SELECT * FROM A JOIN B ON C IN D case e join t left outer join INner join right join [case] -> SELECT * FROM A JOIN B ON C IN D CASE e join t left outer join INner join right join [join] -> SELECT * FROM A JOIN B ON C IN D CASE e join t left external join INner join right join [left] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT external join INner join right join [outer] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INNER JOIN right join [join] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INNER JOIN right join [inner] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INner join right join [join] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INNER JOIN right join [right] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INNER JOIN RIGHT JOIN [join] -> SELECT * FROM A JOIN B ON C IN D CASE e join t LEFT OUTER JOIN INNER JOIN RIGHT JOIN

您可以在第 5 行看到当 in 被 IN 替换时；然后 join 被替换为 joIN

然后，发生的事情是您对 Keywords.Any 的调用正常工作，并且匹配 join 和 joIN，但是，replace 调用仍然区分大小写，替换不会发生。

替换是 C# 区分大小写，不幸的是，.NET 不提供不区分大小写的版本；但是有一些解决方案。

检查 this link 以获取不区分大小写替换的实现。

Answer 4

问题是您已经替换了联接中的 IN。因此，当您想用 JOIN 替换 join 时，比较失败。 （加入！= 加入）

Answer 5

如果你调试它，你会注意到你的关键字“in”替换了第二个连接，所以你得到了 join。稍后您的文本变量将尝试将“join”替换为“JOIN”，但它不会找到“join”，因为它的一部分是大写的。