Q47563: CTRL+A and CTRL+B Bytes Stripped from String Constants in .EXE

Article: Q47563
Product(s): See article
Version(s): 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890721-81 B_BasicCom | mspl13_basic
Last Modified: 29-JAN-1991

BC.EXE in QuickBASIC version 4.50 strips out the characters CTRL+A and
CTRL+B (ASCII 1 and 2) from quoted strings at compile time, whereas
QB.EXE allows these characters. Inside QB.EXE, a CONST or a variable
assigned a value of a literal STRING consisting of the CTRL+A or
CTRL+B characters correctly has both a length and a graphics
representation. In an .EXE program compiled with BC.EXE, neither one
has a length or a graphics representation. This is a limitation with
BC.EXE in QuickBASIC version 4.50, but not with earlier versions.

This design limitation also applies to BC.EXE in Microsoft BASIC
Professional Development System (PDS) versions 7.00 and 7.10 for
MS-DOS and MS OS/2. QBX.EXE 7.00 and 7.10 allows ASCII 1 and 2 values
in quoted strings.

BC.EXE reserves the ASCII 1 and 2 bytes to internally represent
end-of-statement and end-of-line. QB.EXE and QBX.EXE are more lenient
in allowing ASCII 1 and 2 bytes to be used in strings.

Code Example
------------

To enter the ASCII character 01 or 02 (smiley or inverse smiley face)
into a quoted string within the QB.EXE or QBX.EXE environment, you
must press CTRL+P followed by CTRL+A or CTRL+B. In the following
program, the caret symbol (^) represents holding down the CTRL key
while pressing the next key:

   CONST a = "^P^A"    ' Smiley face representation of CTRL+A
   CONST b = "^P^B"    ' Inverse smiley face representation of CTRL+B

   a1$ = "^P^A"
   b1$ = "^P^B"

   PRINT a, a1$, CHR$(1), LEN(a1$)
   PRINT b, b1$, CHR$(2), LEN(b1$)

Note that the functions CHR$(1) and CHR$(2) return the same ASCII
values (01 and 02) at run time as pressing CTRL+A and CTRL+B at edit
time. The problem does not occur if you print the function CHR$(1) or
CHR$(2), or assign either to a string variable. To work around the
problem, assign CHR$(1) and CHR$(2) to a string variable (but not to a
CONST constant). For example:

   a1$ = CHR$(1)
   b1$ = CHR$(2)
   PRINT a1$, CHR$(1), LEN(a1$)   ' Works fine in .EXE
   PRINT b1$, CHR$(2), LEN(b1$)   ' Works fine in .EXE

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