fltk/documentation/editor.html

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<H1 ALIGN="RIGHT"><A NAME="editor">4 - Designing a Simple Text Editor</A></H1>

<P>This chapter takes you through the design of a simple
FLTK-based text editor.

<H2>Determining the Goals of the Text Editor</H2>

<P>Since this will be the first big project you'll be doing with FLTK,
lets define what we want our text editor to do:

<OL>

	<LI>Provide a menubar/menus for all functions.</LI>
	<LI>Edit a single text file, possibly with multiple views.</LI>
	<LI>Load from a file.</LI>
	<LI>Save to a file.</LI>
	<LI>Cut/copy/delete/paste functions.</LI>
	<LI>Search and replace functions.</LI>
	<LI>Keep track of when the file has been changed.</LI>

</OL>

<H2>Designing the Main Window</H2>

<P>Now that we've outlined the goals for our editor, we can begin with
the design of our GUI. Obviously the first thing that we need is a
window, which we'll place inside a class called <TT>EditorWindow</TT>:

<UL><PRE>
class EditorWindow : public Fl_Double_Window {
  public:
    EditorWindow(int w, int h, const char* t);
    ~EditorWindow();

    Fl_Window          *replace_dlg;
    Fl_Input           *replace_find;
    Fl_Input           *replace_with;
    Fl_Button          *replace_all;
    Fl_Return_Button   *replace_next;
    Fl_Button          *replace_cancel;

    Fl_Text_Editor     *editor;
    char               search[256];
};
</PRE></UL>

<H2>Variables</H2>

<P>Our text editor will need some global variables to keep track of
things:

<UL><PRE>
int            changed = 0;
char           filename[256] = &quot;&quot;;
Fl_Text_Buffer *textbuf;
</PRE></UL>

<P>The <TT>textbuf</TT> variable is the text editor buffer for
our window class described previously. We'll cover the other
variables as we build the application.</P>

<H2>Menubars and Menus</H2>

<P>The first goal requires us to use a menubar and menus that
define each function the editor needs to perform. The <A
href="Fl_Menu_Item.html"><TT>Fl_Menu_Item</TT></A> structure is
used to define the menus and items in a menubar:</P>

<UL><PRE>
Fl_Menu_Item menuitems[] = {
  { "&amp;File",              0, 0, 0, FL_SUBMENU },
    { "&amp;New File",        0, (Fl_Callback *)new_cb },
    { "&amp;Open File...",    FL_CTRL + 'o', (Fl_Callback *)open_cb },
    { "&amp;Insert File...",  FL_CTRL + 'i', (Fl_Callback *)insert_cb, 0, FL_MENU_DIVIDER },
    { "&amp;Save File",       FL_CTRL + 's', (Fl_Callback *)save_cb },
    { "Save File &amp;As...", FL_CTRL + FL_SHIFT + 's', (Fl_Callback *)saveas_cb, 0, FL_MENU_DIVIDER },
    { "New &amp;View", FL_ALT + 'v', (Fl_Callback *)view_cb, 0 },
    { "&amp;Close View", FL_CTRL + 'w', (Fl_Callback *)close_cb, 0, FL_MENU_DIVIDER },
    { "E&amp;xit", FL_CTRL + 'q', (Fl_Callback *)quit_cb, 0 },
    { 0 },

  { "&amp;Edit", 0, 0, 0, FL_SUBMENU },
    { "&amp;Undo",       FL_CTRL + 'z', (Fl_Callback *)undo_cb, 0, FL_MENU_DIVIDER },
    { "Cu&amp;t",        FL_CTRL + 'x', (Fl_Callback *)cut_cb },
    { "&amp;Copy",       FL_CTRL + 'c', (Fl_Callback *)copy_cb },
    { "&amp;Paste",      FL_CTRL + 'v', (Fl_Callback *)paste_cb },
    { "&amp;Delete",     0, (Fl_Callback *)delete_cb },
    { 0 },

  { "&amp;Search", 0, 0, 0, FL_SUBMENU },
    { "&amp;Find...",       FL_CTRL + 'f', (Fl_Callback *)find_cb },
    { "F&amp;ind Again",    FL_CTRL + 'g', find2_cb },
    { "&amp;Replace...",    FL_CTRL + 'r', replace_cb },
    { "Re&amp;place Again", FL_CTRL + 't', replace2_cb },
    { 0 },

  { 0 }
};
</PRE></UL>

<P>Once we have the menus defined we can create the
<TT>Fl_Menu_Bar</TT> widget and assign the menus to it with:</P>

<UL><PRE>
Fl_Menu_Bar *m = new Fl_Menu_Bar(0, 0, 512, 30);
m-&gt;copy(menuitems);
</PRE></UL>

<P>We'll define the callback functions later.

<H2>Editing the Text</H2>

<P>To keep things simple our text editor will use the
<A HREF="Fl_Text_Editor.html"><TT>Fl_Text_Editor</TT></A>
widget to edit the text:

<UL><PRE>
w->editor = new Fl_Text_Editor(0, 30, 512, 354);
w->editor->buffer(textbuf);
</PRE></UL>

<P>So that we can keep track of changes to the file, we also want to add
a &quot;modify&quot; callback:</P>

<UL><PRE>
textbuf->add_modify_callback(changed_cb, w);
textbuf->call_modify_callbacks();
</PRE></UL>

<P>Finally, we want to use a mono-spaced font like <TT>FL_COURIER</TT>:

<UL><PRE>
w->editor->textfont(FL_COURIER);
</PRE></UL>

<H2>The Replace Dialog</H2>

<P>We can use the FLTK convenience functions for many of the
editor's dialogs, however the replace dialog needs its own
custom window.  To keep things simple we will have a
&quot;find&quot; string, a &quot;replace&quot; string, and
&quot;replace all&quot;, &quot;replace next&quot;, and
&quot;cancel&quot; buttons.  The strings are just
<TT>Fl_Input</TT> widgets, the &quot;replace all&quot; and
&quot;cancel&quot; buttons are <TT>Fl_Button</TT> widgets, and
the &quot;replace next &quot; button is a
<TT>Fl_Return_Button</TT> widget:</P>

<P ALIGN="CENTER"><IMG src="editor-replace.gif" ALT="The search and replace dialog."><BR>
<I>Figure 4-1: The search and replace dialog.</I></P>

<UL><PRE>
Fl_Window *replace_dlg = new Fl_Window(300, 105, &quot;Replace&quot;);
Fl_Input *replace_find = new Fl_Input(70, 10, 200, 25, &quot;Find:&quot;);
Fl_Input *replace_with = new Fl_Input(70, 40, 200, 25, &quot;Replace:&quot;);
Fl_Button *replace_all = new Fl_Button(10, 70, 90, 25, &quot;Replace All&quot;);
Fl_Button *replace_next = new Fl_Button(105, 70, 120, 25, &quot;Replace Next&quot;);
Fl_Button *replace_cancel = new Fl_Button(230, 70, 60, 25, &quot;Cancel&quot;);
</PRE></UL>

<H2>Callbacks</H2>

<P>Now that we've defined the GUI components of our editor, we
need to define our callback functions.</P>

<H3>changed_cb()</H3>

<P>This function will be called whenever the user changes any text in the
<TT>editor</TT> widget:

<UL><PRE>
void changed_cb(int, int nInserted, int nDeleted,int, const char*, void* v) {
  if ((nInserted || nDeleted) && !loading) changed = 1;
  EditorWindow *w = (EditorWindow *)v;
  set_title(w);
  if (loading) w->editor->show_insert_position();
}
</PRE></UL>

<P>The <TT>set_title()</TT> function is one that we will write to set
the changed status on the current file.  We're doing it this way
because we want to show the changed status in the window's
title bar.

<H3>copy_cb()</H3>

<P>This callback function will call <A
href="Fl_Text_Editor.html#Fl_Text_Editor.kf_copy"><TT>kf_copy()</TT></A>
to copy the currently selected text to the clipboard:</P>

<UL><PRE>
void copy_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  Fl_Text_Editor::kf_copy(0, e->editor);
}
</PRE></UL>

<H3>cut_cb()</H3>

<P>This callback function will call <A
href="Fl_Text_Editor.html#Fl_Text_Editor.kf_cut"><TT>kf_cut()</TT></A>
to cut the currently selected text to the clipboard:</P>

<UL><PRE>
void cut_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  Fl_Text_Editor::kf_cut(0, e->editor);
}
</PRE></UL>

<H3>delete_cb()</H3>

<P>This callback function will call <A
href="Fl_Text_Buffer.html#Fl_Text_Buffer.remove_selection"><TT>remove_selection()</TT></A>
to delete the currently selected text to the clipboard:</P>

<UL><PRE>
void delete_cb(Fl_Widget*, void* v) {
  textbuf->remove_selection();
}
</PRE></UL>

<H3>find_cb()</H3>

<P>This callback function asks for a search string using the <A
href="functions.html#fl_input2"><TT>fl_input()</TT></A>
convenience function and then calls the <TT>find2_cb()</TT>
function to find the string:

<UL><PRE>
void find_cb(Fl_Widget* w, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  const char *val;

  val = fl_input("Search String:", e->search);
  if (val != NULL) {
    // User entered a string - go find it!
    strcpy(e->search, val);
    find2_cb(w, v);
  }
</PRE></UL>

<H3>find2_cb()</H3>

<P>This function will find the next occurrence of the search
string. If the search string is blank then we want to pop up the
search dialog:

<UL><PRE>
void find2_cb(Fl_Widget* w, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  if (e->search[0] == '\0') {
    // Search string is blank; get a new one...
    find_cb(w, v);
    return;
  }

  int pos = e->editor->insert_position();
  int found = textbuf->search_forward(pos, e->search, &pos);
  if (found) {
    // Found a match; select and update the position...
    textbuf->select(pos, pos+strlen(e->search));
    e->editor->insert_position(pos+strlen(e->search));
    e->editor->show_insert_position();
  }
  else fl_alert("No occurrences of \'%s\' found!", e->search);
}
</PRE></UL>

<P>If the search string cannot be found we use the <A
href="functions.html#fl_alert"><TT>fl_alert()</TT></A>
convenience function to display a message to that effect.

<H3>new_cb()</H3>
<P>This callback function will clear the editor widget and current
filename. It also calls the <TT>check_save()</TT> function to give the
user the opportunity to save the current file first as needed:

<UL><PRE>
void new_cb(Fl_Widget*, void*) {
  if (!check_save()) return;

  filename[0] = '\0';
  textbuf->select(0, textbuf->length());
  textbuf->remove_selection();
  changed = 0;
  textbuf->call_modify_callbacks();
}
</PRE></UL>

<H3>open_cb()</H3>

<P>This callback function will ask the user for a filename and then load
the specified file into the input widget and current filename. It also
calls the <TT>check_save()</TT> function to give the user the
opportunity to save the current file first as needed:

<UL><PRE>
void open_cb(Fl_Widget*, void*) {
  if (!check_save()) return;

  char *newfile = fl_file_chooser("Open File?", "*", filename);
  if (newfile != NULL) load_file(newfile, -1);
}
</PRE></UL>

<P>We call the <TT>load_file()</TT> function to actually load the file.

<H3>paste_cb()</H3>

<P>This callback function will call <A
href="Fl_Text_Editor.html#Fl_Text_Editor.kf_paste"><TT>kf_paste()</TT></A>
to paste the clipboard at the current position:</P>

<UL><PRE>
void paste_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  Fl_Text_Editor::kf_paste(0, e->editor);
}
</PRE></UL>

<H3>quit_cb()</H3>

<P>The quit callback will first see if the current file has been
modified, and if so give the user a chance to save it. It then exits
from the program:

<UL><PRE>
void quit_cb(Fl_Widget*, void*) {
  if (changed && !check_save())
    return;

  exit(0);
}
</PRE></UL>

<H3>replace_cb()</H3>

<P>The replace callback just shows the replace dialog:

<UL><PRE>
void replace_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  e-&gt;replace_dlg-&gt;show();
}
</PRE></UL>

<H3>replace2_cb()</H3>

<P>This callback will replace the next occurence of the replacement
string. If nothing has been entered for the replacement string, then
the replace dialog is displayed instead:

<UL><PRE>
void replace2_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  const char *find = e-&gt;replace_find-&gt;value();
  const char *replace = e-&gt;replace_with-&gt;value();

  if (find[0] == '\0') {
    // Search string is blank; get a new one...
    e-&gt;replace_dlg-&gt;show();
    return;
  }

  e-&gt;replace_dlg-&gt;hide();

  int pos = e-&gt;editor-&gt;insert_position();
  int found = textbuf-&gt;search_forward(pos, find, &amp;pos);

  if (found) {
    // Found a match; update the position and replace text...
    textbuf-&gt;select(pos, pos+strlen(find));
    textbuf-&gt;remove_selection();
    textbuf-&gt;insert(pos, replace);
    textbuf-&gt;select(pos, pos+strlen(replace));
    e-&gt;editor-&gt;insert_position(pos+strlen(replace));
    e-&gt;editor-&gt;show_insert_position();
  }
  else fl_alert(&quot;No occurrences of \'%s\' found!&quot;, find);
}
</PRE></UL>

<H3>replall_cb()</H3>

<P>This callback will replace all occurences of the search
string in the file:

<UL><PRE>
void replall_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  const char *find = e-&gt;replace_find-&gt;value();
  const char *replace = e-&gt;replace_with-&gt;value();

  find = e-&gt;replace_find-&gt;value();
  if (find[0] == '\0') {
    // Search string is blank; get a new one...
    e-&gt;replace_dlg-&gt;show();
    return;
  }

  e-&gt;replace_dlg-&gt;hide();

  e-&gt;editor-&gt;insert_position(0);
  int times = 0;

  // Loop through the whole string
  for (int found = 1; found;) {
    int pos = e-&gt;editor-&gt;insert_position();
    found = textbuf-&gt;search_forward(pos, find, &amp;pos);

    if (found) {
      // Found a match; update the position and replace text...
      textbuf-&gt;select(pos, pos+strlen(find));
      textbuf-&gt;remove_selection();
      textbuf-&gt;insert(pos, replace);
      e-&gt;editor-&gt;insert_position(pos+strlen(replace));
      e-&gt;editor-&gt;show_insert_position();
      times++;
    }
  }

  if (times) fl_message(&quot;Replaced %d occurrences.&quot;, times);
  else fl_alert(&quot;No occurrences of \'%s\' found!&quot;, find);
}
</PRE></UL>

<H3>replcan_cb()</H3>

<P>This callback just hides the replace dialog:

<UL><PRE>
void replcan_cb(Fl_Widget*, void* v) {
  EditorWindow* e = (EditorWindow*)v;
  e-&gt;replace_dlg-&gt;hide();
}
</PRE></UL>

<H3>save_cb()</H3>

<P>This callback saves the current file.  If the current filename is
blank it calls the &quot;save as&quot; callback:

<UL><PRE>
void save_cb(void) {
  if (filename[0] == '\0') {
    // No filename - get one!
    saveas_cb();
    return;
  }
  else save_file(filename);
}
</PRE></UL>

<P>The <TT>save_file()</TT> function saves the current file to the
specified filename.

<H3>saveas_cb()</H3>

<P>This callback asks the user for a filename and saves the current file:

<UL><PRE>
void saveas_cb(void) {
  char *newfile;

  newfile = fl_file_chooser(&quot;Save File As?&quot;, &quot;*&quot;, filename);
  if (newfile != NULL) save_file(newfile);
}
</PRE></UL>

<P>The <TT>save_file()</TT> function saves the current file to the
specified filename.

<H2>Other Functions</H2>

<P>Now that we've defined the callback functions, we need our support
functions to make it all work:

<H3>check_save()</H3>

<P>This function checks to see if the current file needs to be saved.  If
so, it asks the user if they want to save it:

<UL><PRE>
int check_save(void) {
  if (!changed) return 1;

  int r = fl_choice(&quot;The current file has not been saved.\n&quot;
                    &quot;Would you like to save it now?&quot;,
                    &quot;Cancel&quot;, &quot;Save&quot;, &quot;Discard&quot;);

  if (r == 1) {
    save_cb(); // Save the file...
    return !changed;
  }

  return (r == 2) ? 1 : 0;
}
</PRE></UL>

<H3>load_file()</H3>

<P>This function loads the specified file into the <TT>textbuf</TT> class:

<UL><PRE>
int loading = 0;
void load_file(char *newfile, int ipos) {
  loading = 1;
  int insert = (ipos != -1);
  changed = insert;
  if (!insert) strcpy(filename, &quot;&quot;);
  int r;
  if (!insert) r = textbuf-&gt;loadfile(newfile);
  else r = textbuf-&gt;insertfile(newfile, ipos);
  if (r)
    fl_alert(&quot;Error reading from file \'%s\':\n%s.&quot;, newfile, strerror(errno));
  else
    if (!insert) strcpy(filename, newfile);
  loading = 0;
  textbuf-&gt;call_modify_callbacks();
}
</PRE></UL>

<P>When loading the file we use the <A
href="Fl_Text_Buffer.html#Fl_Text_Buffer.loadfile"><TT>loadfile()</TT></A>
method to &quot;replace&quot; the text in the buffer, or the <A
href="Fl_Text_Buffer.html#Fl_Text_Buffer.insertfile"><TT>insertfile()</TT></A>
method to insert text in the buffer from the named file.

<H3>save_file()</H3>

<P>This function saves the current buffer to the specified file:

<UL><PRE>
void save_file(char *newfile) {
  if (textbuf-&gt;savefile(newfile))
    fl_alert(&quot;Error writing to file \'%s\':\n%s.&quot;, newfile, strerror(errno));
  else
    strcpy(filename, newfile);
  changed = 0;
  textbuf-&gt;call_modify_callbacks();
}
</PRE></UL>

<H3>set_title()</H3>

<P>This function checks the <TT>changed</TT> variable and updates the
window label accordingly:
<UL><PRE>
void set_title(Fl_Window* w) {
  if (filename[0] == '\0') strcpy(title, "Untitled");
  else {
    char *slash;
    slash = strrchr(filename, '/');
#ifdef WIN32
    if (slash == NULL) slash = strrchr(filename, '\\');
#endif
    if (slash != NULL) strcpy(title, slash + 1);
    else strcpy(title, filename);
  }

  if (changed) strcat(title, " (modified)");

  w->label(title);
}
</PRE></UL>

<H2>Compiling the Editor</H2>

<P>The complete source for our text editor can be found in the <TT>test/editor.cxx</TT> source file.  Both the Makefile and Visual C++
workspace include the necessary rules to build the editor.  You can
also compile it using a standard compiler with:

<UL><PRE>
CC -o editor editor.cxx -lfltk -lXext -lX11 -lm
</PRE></UL>

<P>or by using the <TT>fltk-config</TT> script with:

<UL><PRE>
fltk-config --compile editor.cxx
</PRE></UL>

<P>As noted in <A href="basics.html">Chapter 1</A>, you may need to
include compiler and linker options to tell them where to find the FLTK
library. Also, the <TT>CC</TT> command may also be called <TT>gcc</TT>
or <TT>c++</TT> on your system.

<P>Congratulations, you've just built your own text editor!</P>

<H2>The Final Product</H2>

The final editor window should look like the image in Figure 4-2.

<P ALIGN="CENTER"><IMG src="editor.gif" ALT="The completed editor window."><BR>
<I>Figure 4-2: The completed editor window</I></P>

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