Q41536: PRINT TAB Can Change Value of Parameter in Subprogram
Article: Q41536 Product(s): See article Version(s): 4.50 Operating System(s): MS-DOS Keyword(s): ENDUSER | buglist4.50 SR# S890216-214 | mspl13_basic Last Modified: 14-FEB-1991 The code below demonstrates that a variable that has been passed to a subprogram procedure may incorrectly be changed by a PRINT TAB(n) statement. However, the same statement in the main module does not cause the error. The problem can be avoided by not using the PRINT TAB(n) statement, or by assigning a local variable to the passed parameter in the SUB and using the local variable in the PRINT TAB(n) statement, or by compiling with the BC /X option. (The /X compiler switch is normally used only to flag an ON ERROR statement with RESUME, RESUME NEXT, or RESUME 0.) Microsoft has confirmed this to be a problem in an .EXE program compiled with BC.EXE in QuickBASIC version 4.50. No problem occurs in the QB.EXE environment. We are researching this problem and will post new information here as it becomes available. The program example below works correctly with all versions of QuickBASIC earlier than version 4.50. Code Example ------------ DECLARE SUB testsub (row%) row% = 9 ' this line is ok -- it is in the main module LOCATE row%, 1: PRINT "main line row%= "; row%; TAB(38); row%; row% = 10 CALL testsub(row%) END SUB testsub (row%) LOCATE row%, 1: PRINT "Sub row%= "; row%; ' The value of row% prints incorrectly: PRINT TAB(38); "row now = "; row% END SUB To work around the problem in QuickBASIC 4.50, print a local variable instead of the passed parameter, for example: SUB testsub (row%) x%=row% LOCATE row%, 1: PRINT "Sub row%= "; row%; PRINT TAB(38); "row now = "; x% ' x% prints ok. END SUB
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