Implement the message handlers for WM_CHAR

By olaf , 3 July 2025

The method OnChar controls the input. Depending on the input it acts in different ways.:

When the input char is a number, a minus or a control code CHertzEdit calls the base class CEdit. This guarantees the usual behaviour of the control for this input
When the input char is a period, OnChar() checks the presence of another period in the control. When a period already exists, the input is ignored, otherwise accepted (Call of CEdit::OnChar).
When the input char is a character that can be converted to a unit code, the current unit is truncated and replaced with a new one that is buid from the input.
All other input is ignored by not calling the base class.

void CHertzEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)
{
        if (iscntrl(nChar))
        {
                CEdit::OnChar(nChar, nRepCnt, nFlags);
                return;
        }

        CString str_nChar(nChar);
        CString strZiel;
        if (m_bNegativAllowed)
                strZiel=str_nChar.SpanIncluding("0123456789kKmMhHzZ.-");
        else
                strZiel=str_nChar.SpanIncluding("0123456789kKmMhHzZ.");

        // Ist nChar a valid input (s.a.) ?
        if (strZiel.IsEmpty())
                return;

        // Ist nChar eine number ?
        strZiel=str_nChar.SpanIncluding(".kKmMhHzZ");
        if (strZiel.IsEmpty()) {
                // yes // Base class
                CEdit::OnChar(nChar, nRepCnt, nFlags);
                return;
        }

        // Get the content of the control
        int nTextLen=GetWindowTextLength();
        char* pChar=new char[nTextLen+1]; // incl. abschliessender \0
        GetWindowText(pChar, nTextLen+1);
        CString strText(pChar);

delete[] pChar;

        if (nChar=='.') {
                // is there a period?
                if (strText.Find('.')== -1) {
                         // no -> base class
                         CEdit::OnChar(nChar, nRepCnt, nFlags);
                        return;
                } else {
                        // no -> ignore
                        return;
                }
        }

BOOL wasK, wasM, wasHz;

        // remove the unit successive
        if (strText.Remove('m') || strText.Remove('M')) wasM=TRUE;
            else wasM=FALSE;
        if (strText.Remove('k') || strText.Remove('K')) wasK=TRUE;
            else wasK=FALSE;
        if (strText.Remove('h') || strText.Remove('H')) wasHz=TRUE;
            else wasHz=FALSE;
        if ((strText.Remove('z') || strText.Remove('Z')) && wasHz)
                wasHz=TRUE;
        else
                wasHz=FALSE;

strText.Remove(' ');

        if (nChar=='k' || nChar=='K') {
                strText+=" KHz";
                SetWindowText(strText);
                SetModify();
                return;
        }
        if (nChar=='m' || nChar=='M') {
                strText+=" MHz";
                SetWindowText(strText);
                SetModify();
                return;
        }
        if (nChar=='h' || nChar=='H' || nChar=='z' || nChar=='Z') {
                if (wasK) {
                        strText+=" KHz";
                        SetWindowText(strText);
                        SetModify();
                        return;
                }
                if (wasM) {
                        strText+=" MHz";
                        SetWindowText(strText);
                        SetModify();
                        return;
                }
                strText+=" Hz";
                SetWindowText(strText);
                SetModify();
                return;
        }
        ASSERT(FALSE); // should never happen
}