_C PROGRAMMING COLUMN_
by Al Stevens

Listing One

// -------- editbox.h 
#ifndef EDITBOX_H
#define EDITBOX_H

#include "textbox.h"

class EditBox : public TextBox    {
    void OpenWindow();
protected:
    int column;       // Current column
    Bool changed;     // True if text has changed
    Bool insertmode;  // True if in insert mode
    virtual void Home();
    virtual void End();
    virtual void NextWord();
    virtual void PrevWord();
    virtual void Forward();
    virtual void Backward();
    virtual void DeleteCharacter();
    virtual void InsertCharacter(int key);
public:
    EditBox(const char *ttl, int lf, int tp, int ht, int wd, DFWindow *par=0)
                        : TextBox(ttl, lf, tp, ht, wd, par)
            { OpenWindow(); }
    EditBox(const char *ttl, int ht, int wd, DFWindow *par=0)
                        : TextBox(ttl, ht, wd, par)
            { OpenWindow(); }
    EditBox(int lf, int tp, int ht, int wd, DFWindow *par=0)
                        : TextBox(lf, tp, ht, wd, par)
            { OpenWindow(); }
    EditBox(int ht, int wd, DFWindow *par=0) : TextBox(ht, wd, par)
            { OpenWindow(); }
    EditBox(const char *ttl) : TextBox(ttl)
            { OpenWindow(); }
    // -------- API messages
    virtual Bool SetFocus();
    virtual void ResetFocus();
    virtual void SetCursor(int x, int y);
    virtual void ResetCursor();
    virtual void SetCursorSize();
    virtual unsigned char CurrentChar()
            { return (*text)[column]; }
    virtual unsigned CurrentCharPosition()
            { return column; }
    virtual Bool AtBufferStart()
            { return (Bool) (column == 0); }
    virtual void Keyboard(int key);
    virtual void Move(int x, int y);
    virtual void Paint();
    virtual void PaintCurrentLine()
            { Paint(); }
    virtual void ClearText();
    virtual void LeftButton(int mx, int my);
    Bool Changed()
            { return changed; }
    void ClearChanged()
            { changed = False; }
    Bool InsertMode()
            { return insertmode; }
    void SetInsertMode(Bool imode)
            { insertmode = imode; ResetCursor(); }
};
inline Bool isWhite(int ch)
{
    return (Bool)
        (ch == ' ' || ch == '\n' || ch == '\t' || ch == '\r');
}
#endif


Listing Two 

// ------------- editbox.cpp
#include <ctype.h>
#include "desktop.h"
#include "editbox.h"

// ----------- common constructor code
void EditBox::OpenWindow()
{
    windowtype = EditboxWindow;
    column = 0;
    changed = False;
    text = new String(1);
    BuildTextPointers();
}
Bool EditBox::SetFocus()
{
    Bool rtn = TextBox::SetFocus();
    if (rtn)    {
        ResetCursor();
        desktop.cursor().Show();
    }
    return rtn;
}
void EditBox::ResetFocus()
{
    desktop.cursor().Hide();
    TextBox::ResetFocus();
}
// -------- process keystrokes
void EditBox::Keyboard(int key)
{
    int shift = desktop.keyboard().GetShift();
    if ((shift & ALTKEY) == 0)    {
        switch (key)    {
            case HOME:
                Home();
                return;
            case END:
                End();
                return;
            case CTRL_FWD:
                NextWord();
                return;
            case CTRL_BS:
                PrevWord();
                return;
            case FWD:
                Forward();
                return;
            case BS:
                Backward();
                return;
            case RUBOUT:
                if (CurrentCharPosition() == 0)
                    break;
                Backward();
                // --- fall through
            case DEL:
                DeleteCharacter();
                BuildTextPointers();
                PaintCurrentLine();
                return;
            default:
                if (!isprint(key))
                    break;
                // --- printable keys processed by editbox
                InsertCharacter(key);
                BuildTextPointers();
                PaintCurrentLine();
                return;
        }
    }
    TextBox::Keyboard(key);
}
// -------- paint the editbox
void EditBox::Paint()
{
    TextBox::Paint();
    ResetCursor();
}
// -------- move the editbox
void EditBox::Move(int x, int y)
{
    TextBox::Move(x, y);
    ResetCursor();
}
// --------- clear the text from the editbox
void EditBox::ClearText()
{
    TextBox::ClearText();
    OpenWindow();
    ResetCursor();
}
// ----- move cursor to left margin
void EditBox::Home()
{
    column = 0;
    if (wleft)    {
        wleft = 0;
        Paint();
    }
    ResetCursor();
}
// ----- move the cursor to end of line
void EditBox::End()
{
    int ch;
    while ((ch = CurrentChar()) != '\0' && ch != '\n')
        column++;
    if (column - wleft >= ClientWidth())    {
        wleft = column - ClientWidth() + 1;
        Paint();
    }
    ResetCursor();
}
// ---- move the cursor to the next word
void EditBox::NextWord()
{
    while (!isWhite(CurrentChar()) && CurrentChar())
        Forward();
    while (isWhite(CurrentChar()))
        Forward();
}
// ---- move the cursor to the previous word
void EditBox::PrevWord()
{
    Backward();
    while (isWhite(CurrentChar()) && !AtBufferStart())
        Backward();
    while (!isWhite(CurrentChar()) && !AtBufferStart())
        Backward();
    if (isWhite(CurrentChar()))
        Forward();
}
// ---- move the cursor one character to the right
void EditBox::Forward()
{
    if (CurrentChar())    {
        column++;
        if (column-wleft == ClientWidth())
            ScrollLeft();
        ResetCursor();
    }
}
// ---- move the cursor one character to the left
void EditBox::Backward()
{
    if (column)    {
        if (column == wleft)
            ScrollRight();
        --column;
        ResetCursor();
    }
}
// ---- insert a character into the edit buffer
void EditBox::InsertCharacter(int key)
{
    unsigned col = CurrentCharPosition();
    if (insertmode || CurrentChar() == '\0')    {
        // ---- shift the text to make room for new character
        String ls, rs;
        if (col)
            ls = text->left(col);
        int rt = text->Strlen()-col;
        if (rt > 0)
            rs = text->right(rt);
        *text = ls + " " + rs;
    }
    (*text)[col] = (char) key;
    if (key == '\n')
        BuildTextPointers();
    Forward();
    changed = True;
}
// ---- delete a character from the edit buffer
void EditBox::DeleteCharacter()
{
    if (CurrentChar())    {
        String ls, rs;
        unsigned col = CurrentCharPosition();
        if (col)
            ls = text->left(col);
        int rt = text->Strlen()-col-1;
        if (rt > 0)
            rs = text->right(rt);
        *text = ls + rs;
        changed = True;
    }
}
// ---- position the cursor
void EditBox::SetCursor(int x, int y)
{
    desktop.cursor().SetPosition(
        x+ClientLeft()-wleft, y+ClientTop()-wtop);
}
// ---- left mouse button was pressed
void EditBox::LeftButton(int mx, int my)
{
    if (ClientRect().Inside(mx, my))    {
        column = max(0, min(text->Strlen()-1,
                          mx-ClientLeft()+wleft));
        ResetCursor();
    }
    else
        TextBox::LeftButton(mx, my);
}
// ---- set the size of the cursor
void EditBox::SetCursorSize()
{
    if (insertmode)
        desktop.cursor().BoxCursor();
    else 
        desktop.cursor().NormalCursor();
}
// ---- reset the cursor
void EditBox::ResetCursor()
{
    SetCursorSize();
    if (visible)
        SetCursor(column, 0);
}



Example 1: The compile problem in (a) dodged by the using the 
member pointer with the <T> qualification in (b).

(a)

template <class T>
class Foo   {
    Foo *nextfoo;
    // ...
};

  
(b)
       
Foo<T> *nextfoo;
            

Example 2: The template function


template <class T>
void Foo(T *tp)
{
    *tp = 321;
}
template <class T>
void Bar(T& tr)
{
    Foo(&tr);
}

main()
{

    int x = 123;
    Bar(x);
}



Example 3: The compiler declares a fatal compile error if a non-
void function fails to return something in (a) although this 
contradicts the ARM rule in (b).


(a)
            
#include <iostream.h>
main()
{
    cout << "Hello, Timna";
}



(b)            

extern f();
main() { }