Microsoft KB Archive/47563

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

Article ID: 47563

Article Last Modified on 11/21/2006

This article was previously published under Q47563


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

Additional query words: QuickBas BasicCom

Keywords: KB47563