Use wildcard to compare string and validate input

Introduction

This article was inspired by Jack Handy (Wildcard string compare).

It describes a function to compare strings with wildcards. I have modified Jack's function to use MFC and use optional character in the wildcard string.

Wildcard sample

If you want to check a string like 'test' or 'tet', you may use the wildcard like this : te^st where ^ indicates an optional char.

I included another parameter to limit characters used in wildcard * or ?.

if (WildMatch("^-*?^.*", sValue, "0123456789")) {
    MessageBox("OK you have a real");
} else {
    MessageBox("Not a real");
}

This sample validates the string in sValue has a good format to be a real number.

Function code

BOOL WildMatch(CString sWild, CString sString, CString sLimitChar)
{
    BOOL bAny = FALSE;
    BOOL bNextIsOptional = FALSE;
    BOOL bAutorizedChar = TRUE;

    int i=0;
    int j=0;

    // Check all the string char by char

    while (i<sString.GetLength()) 
    {
      // Check index for array overflow

      if (j<sWild.GetLength())
      {
          // Manage '*' in the wildcard

          if (sWild[j]=='*') 
          {
          // Go to next character in the wildcard

          j++;

          // Enf of the string and wildcard end 

          // with *, only test string validity

          if (j>=sWild.GetLength()) 
          {
          // Check end of the string

          while (!sLimitChar.IsEmpty() && i<sString.GetLength()) 
          {
          // If this char is not ok, return false

          if (sLimitChar.Find(sString[i])<0)
              return FALSE;

          i++;
          }

          return TRUE;
          }

          bAny = TRUE;
          bNextIsOptional = FALSE;
          } 
          else 
          {
              // Optional char in the wildcard

              if (sWild[j]=='^')
              {
              // Go to next char in the wildcard and indicate 

              // that the next is optional

              j++;
 
              bNextIsOptional = TRUE;
              }
              else
              {
                bAutorizedChar = 
                  ((sLimitChar.IsEmpty()) || (sLimitChar.Find(sString[i])>=0));

                // IF :

                  if (// Current char match the wildcard

                    sWild[j] == sString[i] 
                    // '?' is used and current char is in autorized char list

                    || (sWild[j] == '?' && bAutorizedChar)
                    // Char is optional and it's not in the string

                    // and it's necessary to test if '*' make any 

                    // char browsing

                    || (bNextIsOptional && !(bAny && bAutorizedChar))) 
                    {
                    // If current char match wildcard, 

                    // we stop for any char browsing

                    if (sWild[j] == sString[i])
                        bAny = FALSE;

                    // If it's not an optional char who is not present,

                    // go to next

                    if (sWild[j] == sString[i] || sWild[j] == '?')
                        i++;

                    j++;

                    bNextIsOptional = FALSE;
                    } 
                    else
                    // If we are in any char browsing ('*') 

                    // and curent char is autorized

                    if (bAny && bAutorizedChar)
                        // Go to next

                        i++;
                    else
                        return FALSE;
               }
            }
        }
        else
        // End of the wildcard but not the 

        // end of the string => 

        // not matching

        return FALSE;
    }

    if (j<sWild.GetLength() && sWild[j]=='^')
    {
        bNextIsOptional = TRUE;
        j++;
    }


    // If the string is shorter than wildcard 

    // we test end of the 

    // wildcard to check matching

    while ((j<sWild.GetLength() && sWild[j]=='*') || bNextIsOptional)
    {
        j++;
        bNextIsOptional = FALSE;

        if (j<sWild.GetLength() && sWild[j]=='^')
        {
            bNextIsOptional = TRUE;
            j++;
        }
    }

    return j>=sWild.GetLength();
}

CEdit input validation

This sample shows you how to use this function to control input validation in a dynamic way.

Be careful when you define your wildcard, because it must be always true! If you want more advanced testing, don't test in real time but do only when the user validates.

For example, if you use ^-?*^.*, the user can never put the minus sign first, because '?' specifies one char is always necessary!

You can put this code in the OnChar of your CEdit child class, or if you don't want to derive a new class, you can put it in the PreTranslateMessage of the mother window, like:

if (pMsg->message==WM_CHAR && pMsg->hwnd==pEdit->m_hWnd && 
         pMsg->wParam>=32)
{
    // Define parameters

    CString sSaveText="";
    CString sNewText="";
    CString sLimitChar="0123456789";
    CString sWildCard="^-*^.*";
    int iNbMaxChar = 10;

        // If we use only upper case, makeupper

    if (m_bMakeUpper)
        pMsg->wParam = toupper(pMsg->wParam);

    DWORD dwSaveSel = pEdit->GetSel();

    pEdit->GetWindowText(sSaveText);

        // Transmit this char to the CEdit to process it

    pEdit->SendMessage(WM_CHAR, pMsg->wParam, pMsg->lParam);

    pEdit->GetWindowText(sNewText);

        // Check if new text is ok

    if (!WildMatch(m_sWildCard, sNewText, sLimitChar) || 
          sNewText.GetLength()>iNbMaxChar)
    {
                // if not, rollback

        pEdit->SetWindowText(sSaveText);
        pEdit->SetSel(dwSaveSel);
    }
}