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1992-10-19
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Common Questions about QuickBASIC
After spending much time on CompuServe, BIX, the FidoNet
QuickBASIC echo and other national BASIC forums, I've noticed
that there is a lot of repetition. People ask the same
questions, time after time. They must be good questions! Here
is a compilation of a few of the more common questions.
Question:
How can I disable Control-Break?
Answer:
Programs compiled with QuickBASIC or BASCOM usually don't
have to worry about this. Control-Break is disabled unless
you compile with the /D (debug) option. In the event that
you are doing something that QuickBASIC doesn't completely
control, like printing to the screen via DOS functions, this
protection no longer holds. In that case, you may be able
to disable Break by getting DOS to check for it less
frequently. Use the command
BREAK OFF
from a batch file, or execute it from BASIC like so:
SHELL "COMMAND BREAK OFF"
See also the BreakOff routine in my PBClone library.
Question:
How can I get the error level from a SHELLed program? How
can I get my program to return an error level?
Answer:
That requires assembly language. PBClone contains such
routines. Also, newer BASIC compilers let you include an
error level with your END statement.
Question:
How can I read the command line from BASIC?
Answer:
The COMMAND$ function will do it for you. Note that
COMMAND$ doesn't return the exact command line-- it is
trimmed somewhat and capitalized. The QBWiz library can
return the original command line for you.
Question:
How can I get access to COM3 and COM4 for my communications
program?
Answer:
BASIC doesn't provide support for those comm ports.
However, there are many add-on libraries which will let you
do it. Look for BasWiz, QBCOM, or QBSER, among others.
Question:
How can I get a directory listing into an array?
Answer:
If you're using BASCOM/PDS, check the DIR$ function. Also,
most BASIC libraries can do this for you. Another way to do
this is to put the directory listing into a file by
SHELL "DIR *.* >DIRLIST.TXT"
and then read the file into an array. Yet another
alternative is to use the FILES statement on a non-displayed
screen page (if you have a CGA, EGA or VGA) or in invisible
colors (say, black on black), then get the results from the
screen with the SCREEN function.
Question:
How can I see if a file exists?
Answer:
Most BASIC libraries can do this for you. Or, you can use
the directory approach given above. Yet another way to do
it is to try to open the file for input:
ON ERROR GOTO NotFound
OPEN File$ FOR INPUT AS #1
CLOSE #1
Found = -1
Done:
RETURN
NotFound:
Found = 0
RESUME Done
Question:
I'm running out of string space. What can I do?
Answer:
If you have arrays, try moving them outside of the string
space area. Either use REDIM to dimension 'em or use the REM
$DYNAMIC metacommand. If this doesn't help enough, use
fixed-length strings, which are stored outside the regular
string area. Still not enough room? Try Microsoft's PDS or
VB-DOS compilers, or Spectra's PowerBASIC. Also, my BasWiz
library provides "far strings" for QuickBasic.
Question:
I'd like to constantly display the time. What do I do?
Answer:
That's also available in libraries, including PBClone. You
can do it yourself using an approach like this, among other
ways:
ON TIMER(1) GOSUB DisplayTime
TIMER ON
' your program goes here
DisplayTime:
OldRow = CSRLIN
OldCol = POS(0)
LOCATE 25, 70
PRINT TIME$;
LOCATE OldRow, OldCol
RETURN
Question:
I need to know how many days lie in between two dates. How
do I do it?
Answer:
As usual... this is something you can get in a library from
your local BBS. Try PBClone or QB4BAS.
Question:
How can I use ANSI display codes?
Answer:
You need to go through DOS display functions for that to
work. Use this:
OPEN "CON" FOR OUTPUT AS #1
This makes the DOS display functions available as file
(device) number one. You can print to it using normal file
statements:
PRINT #1, CHR$(27); "[2J";
The above statement will clear the screen if an ANSI driver
is installed. See your DOS manual for information on the
available ANSI codes. You can also get this information
from your friendly local BBS.
If you are using the BasWiz library, check out ANSIprint in
the Telecommunications section. It handles ANSI in a
virtual window and also allows for "ANSI" music processing
if desired. ANSI.SYS not needed.
Question:
How can I print the screen to the printer, in text or
graphics mode?
Answer:
One simple solution is to use CALL INTERRUPT. Interrupt
number 5 (five) does the same thing as pressing
PrintScreen/PrtSc on your keyboard. It will handle CGA
graphics as well as text mode if GRAPHICS is installed
(GRAPHICS.COM or GRAPHICS.EXE is provided with DOS).
If you are just using text mode, check into the SCREEN
function, which allows you to read characters off the
display. If you collect each row into a string and then use
RTRIM$ to remove trailing blanks, it'll be faster than
sending all those meaningless blanks to the printer.
Question:
How can I display picture files, like GIF, PCX, MAC, MSP and
so forth?
Answer:
Well, the BasWiz library can help with MAC and PCX files.
Probably the best solution for a general-purpose picture
handler, though, would be to get a copy of OPTIKS (usually
distributed as OK followed by a version number) or another
picture format converter at your local BBS. Image
translation tends to be somewhat difficult and slow in
BASIC, and it's hard to find the information needed to
handle the various formats available. If you can read other
languages than BASIC, you can find source code for various
picture handlers on your local BBS. These are often written
in assembly language, C, and Pascal, which are better for
this specific purpose than BASIC.
Have I mentioned BBSes a lot?! If you don't have a modem, make
the investment! It will be well worth it, whether you are a
serious programmer or just like to fiddle around now and then.
There are vast numbers of files and helpful people within reach
of a telephone call of your computer!