Category : Files from Magazines
Archive   : JAN94.ZIP
Filename : CPROG.ASC

_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
#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 qualification in (b).

(a)

template
class Foo {
Foo *nextfoo;
// ...
};


(b)

Foo *nextfoo;


Example 2: The template function


template
void Foo(T *tp)
{
*tp = 321;
}
template
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
main()
{
cout << "Hello, Timna";
}



(b)

extern f();
main() { }