The Clipboard

By Dave Kelly

One of the features that makes the Macintosh unique from other computers is the use of the clipboard. The clipboard adds flexibility to the Mac user interface. With it you can exchange data from one application to another. Anyone who has worked with MacPaint or MacWrite is familar with the operation of the clipboard. What you cut or copy is saved in the clipboard allowing you to paste it somewhere else! But how do you deal with the clipboard from your own programs? That is the subject we want to explore this month.

Support of the clipboard is another feature of the Macintosh user interface that was left out of MSBASIC version 1.0 but fortunately is easily used in version 2.0. Most of the features that we will use here will only work for version 2.0. There are a few things you should keep in mind when writing programs to use the clipboard.

First, there are three different ways which BASIC can address the clipboard file. Use the OPEN statement with one of the following statements for the filename:

“CLIP:” for transferring data from programs that have tabular data, like Multiplan or Chart.

“CLIP:TEXT” for transfering text to and from word processors and other programs.

“CLIP:PICTURE” for transferring picture data to and from MacPaint or other programs.

Files that are OPENed to this device, using the mode indicated above, will read/write data directly from/to the Clipboard File stored on the system disk.

The sample program ‘Show Clip’ shows how the clipboard could be read within an application and displayed. You have probably seen many applications that give the user the option to “Show Clipboard”. The program will check to see if the clipboard contains picture data or text and will read the data accordingly and display it in the window. This routine is an example to show how to read from the clipboard, but could be used in your own application to produce the “Show Clipboard” option.

When you make use of EDIT FIELDs in your programs you should keep the Edit menu active so that your EDIT FIELD can be fully edited using the cut, copy and paste feature of the Edit menu. This way the clipboard is being used without having to do a whole lot of programing; however the operation is still manual. The user must decide what to select and copy or cut it into the EDIT FIELD. The same is true for inserting text with the paste option.

If the file is opened to “CLIP:” or “CLIP:TEXT”, the data is read sequentially from the clipboard file. There are actually two clipboard areas. One is the clipboard file and the other is a temporary area in memory. That’s why sometimes the disk turns on when you cut or copy something and other times it doesn’t.

To write text to the clipboard:

• Open the clipboard with OPEN “CLIP:” FOR OUTPUT AS #1 or equivalent.

• Use Write #1 or Print #1 to write your variable to the clipboard file.

• CLOSE #1 to close the file.

To read from the clipboard:

• Open the clipboard with OPEN “CLIP:” FOR OUTPUT AS #1 or equivalent.

• Use INPUT #1 to read variables from the clipboard file.

• CLOSE #1 to close the file.

See the program for an example of this.

You should remember to use the proper format when storing data in the clipboard so that other applications may use the data. For example, the text that a word processor uses would contain format control characters imbedded in the text. These kind of characters should only be left in the text stored in the clipboard if you know that the program that will be reading it will use them. Some things might not matter what format they are stored in and the data can be formatted once it has been read into the new application. Most of the applications available will tell you how the data is formatted, so if you know what the data will be used in, there won’t be any problem. Some help on transfering files to and from the clipboard and other applications can be found on page 55 of the BASIC manual.

Copying pictures is just about as easy as text. To transfer something to MacPaint:

• Use the PICTURE ON statement to record the graphics statements.

• Issue all the graphics statements you need to produce the picture. You don’t have to draw it to record it as a picture.

• Use PICTURE OFF to stop recording graphics.

A good example of this is found in the BASIC manual page 205.

• Next open the clipboard file with OPEN “CLIP:PICTURE” FOR OUTPUT AS #1 (or equavalent statement)

• Send the picture to the clipboard with PRINT #1,PICTURE$

• Close the file: CLOSE #1

Next you can either exit BASIC and paste the picture into MacPaint or save the picture in the Scrapbook to use later.

To transfer MacPaint pictures to BASIC:

• Put the MacPaint picture in the Clipboard

• Open the clipboard file with OPEN “CLIP:PICTURE” FOR INPUT AS #1 (or equavalent statement)

• Transfer the picture to a string variable (called image$ in this case): image$=INPUT$(LOF(1),1)

• Close the file: CLOSE #1

• Draw the Picture to the screen exactly the way it was recored: PICTURE,image$

See the program for an example of reading a picture from the clipboard.

To determine if the data in the clipboard is picture or text we can use the BASIC statement LOF. LOF(1) will return the length of the specified file (in this case our file is “CLIP:”. If the result turns out to be zero, it means that either the data is a picture or the clipboard is empty. So next just read whatever picture Is stored, if any. If the clipboard is empty, the resulting string variable will also be empty.

There is one more way to store text or graphics in the clipboard. I’m not sure that there is a good reason to want to do this though. Using a screen GET, a portion of the screen can be copied into a non-string variable array. This variable can be written to the clipboard for later use. You can then read the clipboard and use a screen PUT, to place the data back on the screen. The screen GET and PUT commands are much more useful in moving sections of the screen image. Since the array used is not a string, it is not in the proper format for MacPaint or for PICTURE statements. I tried to use screen GET and PUT to read the picture of Professor Mac found in last month’s Screen Poke article. The problem is that when the image is directly poked on the screen, BASIC doesn’t recognize it as being anything useful. You can’t record pokes with the PICTURE ON/OFF feature of BASIC. Perhaps one of our readers knows how to change the data from a screen GET format to MacPaint picture format. For most programs you will want to use the other methods mentioned anyway.

In conclusion, figure 1 shows the different ways that data can be stored in the clipboard. Most of these methods are explained fairly well in the BASIC 2.0 manual. (ref. pg. 55-58 for more information on tranfering data between BASIC and other programs. Note there is an error on page 58 where it says PICTURE$,IMAGE$ should be PICTURE, IMAGE$. Also see pg. 205 for PICTURE statement.)

‘     Show Clip
‘     By Dave Kelly
‘     ©MACTUTOR 1985

‘Set up windows
WINDOW 1,”Output Window”, (2,40)-(510,200),1
WINDOW 2,”Clipboard File”,  (2,220)-(510,340),1
WINDOW CLOSE 2
‘Set up menus
MENU 4,0,0,””
MENU 5,0,1,”Windows”
MENU 5,1,1,”Output Window”
MENU 5,2,1,”Show Clipboard”
MENU 5,3,1,”Quit”
ON MENU GOSUB handlemenu
MENU ON
ON DIALOG GOSUB handlewindow
DIALOG ON
EDIT FIELD 1,””,(150,42)-(365,120),1
show:GOTO show:GOSUB showclipboard
handlemenu:  ‘Menu handler
number=MENU(0)
IF number<>5 THEN RETURN
item=MENU(1):MENU
IF item=1 THEN WINDOW 1
IF item=2 THEN GOSUB showclipboard
IF item=3 THEN WINDOW CLOSE 2:WINDOW CLOSE 1:MENU RESET: END
RETURN
handlewindow:  ‘Menu handler
stat=DIALOG(0)
IF stat=3 THEN WINDOW DIALOG(3)
IF stat=4 THEN WINDOW CLOSE DIALOG(4)
RETURN
showclipboard:
WINDOW 2:CLS
DIALOG STOP:MENU STOP
‘Read text from clipboard
OPEN “CLIP:TEXT” FOR INPUT AS #1
IF LOF(1)=0 THEN CLOSE #1:GOTO   do.picture
LOCATE 1,1
WHILE NOT EOF(1)
        INPUT #1,a$:PRINT a$
WEND
CLOSE #1:DIALOG ON:MENU ON
RETURN
do.picture:  ‘Read picture from Clipboard
DIALOG STOP:MENU STOP
OPEN “CLIP:PICTURE” FOR INPUT AS #1
        image$=INPUT$(LOF(1),1)
        PICTURE,image$
CLOSE #1:DIALOG ON:MENU ON:RETURN