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我在 C# 中制作了一个电子邮件验证程序，但是如何检查字符串之外的数据？

这是我的 C# 代码：

private bool CheckEmail()
{
    string email1 = email.Text;

    //calculating the length of the email
    int EmailLen = email1.Length;
    int num = 0;

    //the first character of the email must not be the "@"
    if (email1.Substring(0, 1) != "@")
    {
        //checking the email entered after the first character as it is not a "@" so i will start from 1.
        for (int i = 1; i < EmailLen; i++)
        {
            //prevents there from being two "@"next to each other
            if (email1[i] == '@' && (i + 1) < email1.Length && email1[i + 1] != '@')
            {
                //if there is an "@" in the email then num will increase by one
                num = num + 1;

                //now the stored value of i is the position where the "@" is placed. j will be i+2 as there should be at least one character after the "@"
                int j = i + 2;
                if (j < EmailLen)
                {
                    for (int k = j; k < EmailLen; k++)
                    {
                        //when it finds a "." In the email, the character after the "." Should not be empty or have a space, e.g. it should be something like ".com"

                        if (email1[k] == '.' && k + 1 < email1.Length && email1[k + 1] != ' ')
                        {
                            num = num + 1;
                        }
                    }
                }
                else
                {
                    break;
                }
            }
        }
    }
    else
    {
        num = 0;
    }

    //if the num is 2, then the email is valid, otherwise it is invalid.  If the email had more than one "@" for example, the num will be greater than 2.

    if (num == 2)
    {
        return true;
    }
    else
    {
        return false;
    }
}

当我尝试输入“aa@”时，我收到此错误：“索引和长度必须引用字符串中的位置。”</p>

在此处输入图像描述

当我输入 aa@a 时。，我收到此错误：“索引和长度必须引用字符串中的位置。”</p>

在此处输入图像描述

4

2 回答 2

2

您不能访问字符串之外的数据。这是有充分理由的——这样做会违反类型安全性，而类型安全性是 .NET CLR 等虚拟机的主要吸引力。

您只想检查您的界限以确保您没有尝试访问不存在的字符串的一部分。顺便说一句，对于检查单个字符，您完全想要做email1[i], not email1.Substring(i, 1)，所以您没有在左、右和中心构造新的字符串对象。

您的第一个测试应该是：

if (email1[i] == '@' && i + 1 < email1.Length && email1[i + 1] != '@')
于 2013-03-25T20:50:53.670 回答
1

你的问题是

email1.Substring(i + 1, 1)

在 for 循环的最后一次迭代中，i == EmailLen -1。

所以 i + 1 == EmailLen，它是字符串末尾的一个。

于 2013-03-25T20:50:58.733 回答