字符串中的正则表达式

Question

I am trying to write a keylogger, with an intent of just getting the float numbers from keyboard input and with them compute some formula and display to the user. My code so far (the HookCallBack part)

 private static IntPtr HookCallback(
            int nCode, IntPtr wParam, IntPtr lParam)
        {

            string xxx = "";
            if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN)
            {
                int vkCode = Marshal.ReadInt32(lParam);   


                if (((Keys)vkCode).ToString() == "OemPeriod")
                {
                    //Console.Out.Write(".");
                    xxx += ".";
                    xxx.Replace("OemPeriod", ".");
                }
                if (((Keys)vkCode).ToString() == "D1")
                {
                    //Console.Out.Write(".");
                    xxx += "1";
                    xxx.Replace("D1", "1");
                }
                if (((Keys)vkCode).ToString() == "D2")
                {
                    //Console.Out.Write(".");
                    xxx += "2";
                    xxx.Replace("D2", "2");
                }

all the way up to 9 and 0

                }
                if (((Keys)vkCode).ToString() == "Space")
                {
                    //Console.Out.Write(".");
                    xxx += " ";
                    xxx.Replace("Space", " ");
                }


            }


            string test = "2.3 4.5 6.7";   

            Regex regex = new Regex(@"\d+\.\d+");
            var ma2 = regex.Matches(xxx);
            Console.Out.Write(ma2.Count);

            xxx = String.Empty;      

            return CallNextHookEx(_hookID, nCode, wParam, lParam);
        }

My issue is this: im not able to make the regex to work (ma2.Count = 0) with the string xxx (which is the keyboard input from the user), but when i replace xxx with the string test, it works. What im doing wrong. Dont know if i was clear enough. Newbie here.Thks in advance!

Answer 1

Updated:

It looks like this method is being called every time a new key is being called, however, you are updating a local variable called xxx .

Every time this method gets invoked, you are always starting with an empty string. At most, xxx will have 1 character.

You will need store the value of xxx outside the scope of the function.

Not recommended (because you want to avoid static variables for this type of thing), but you could introduce a new variable:

private static string InputFields = "";

and use InputFields += "."; for example.

Also note that xxx.Replace(...) doesn't actually do anything here because you are not assigning the result of this method to anything. You can drop it altogether.

---

As per @CinCout's comment, are you able to verify the value of xxx ?

I tried the example above and it should work with the test input:

using System;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main()
    {
        var test = "2.3 4.5 6.7";
        var regex = new Regex(@"\d+\.\d+");
        var matches = regex.Matches(test);

        foreach (var match in matches)
        {
            Console.WriteLine(match);
        }
    }
}

Demo