C# 烦恼 - 在 sting 之外访问数据

Question

我用C#做了一个邮件验证程序，但是如何检查字符串以外的数据呢？

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，出现此错误:“索引和长度必须引用字符串中的某个位置。”

当我键入 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。”

Answer 1

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，而类型安全是 .NET CLR 等虚拟机的主要吸引力。

您只想检查您的边界以确保您没有尝试访问不存在的字符串部分。顺便说一句，为了检查单个字符，你完全想做 email1[i]，而不是 email1.Substring(i, 1)，所以你不会构造新的字符串左侧、右侧和中心的对象。

你的第一个测试应该是:

if (email1[i] == '@' && i + 1 < email1.Length && email1[i + 1] != '@')