C# simply identifies whether an illegal string exists

IndexOf identifies illegal strings and is simple and easy to understand.

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renderings

Illegal characters in the string can be identified and displayed.

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 Implement code

private string UnlegalString(string str)//过滤非法字符串
        {
            //制定出非法字符串
            string Unlegalstr = "-_*×――(^)$%~!/@#$…&%￥—+=<>《》|!！??？:：•`·、。，；,.;\"‘’“”-]";
            //存储提示用户应该修改的文本
            string UserMsg = "";
            //计数结果
            int res = -1;
            //根据用户输入长度循环
            for (int i = 0; i < str.Length; i++)
            {
                res=Unlegalstr.IndexOf(str[i]);//若是没有则会返回-1
                if (res != -1)//如果不等-1，证明有结果
                {
                    UserMsg += str[i].ToString();//存储结果并返回
                }
                
            }
            if (res > 0)
                return UserMsg;//返回非法字符串
            else
                return "";//没有则不返回
        }

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transfer

private void button1_Click(object sender, EventArgs e)//Button_Click的方法中
        {
            //调用上面的方法，上面方法返回是字符串，这里判断一下是不是返回来空的。
            if (UnlegalString(textBox1.Text) != "")
            {
                //获取非法字符串
                string str = UnlegalString(textBox1.Text);
                MessageBox.Show($"存在非法字符串“{str}”！请修改！", "提示");
            }
            else
            {
                MessageBox.Show("不存在非法字符串", "提示");
            }
        }

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Expand the methods res=Unlegalstr.IndexOf(str[i]);used IndexOf.

String.​Index​Of method

• Refer to official documentation.

definition

• Namespaces:

  System

• Assembly:

  System.Runtime.dll

Reports the zero-based index of the first occurrence of the specified Unicode character or string in this instance. This method returns -1 if the character or string is not found in this instance .