Q33301: FUNCTION Procedures Cannot Be Invoked in I/O Statements

Article: Q33301
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 9-JUL-1990

You should avoid invoking (or nesting) a FUNCTION procedure in a BASIC
statement that performs output to a file. Instead, the returned value
of the FUNCTION procedure should be assigned to an intermediate
variable, and the intermediate variable can then be used in the I/O
statement. (A FUNCTION procedure is defined in a FUNCTION...END
FUNCTION block.)

This and other restrictions are described on Page 201 of the
"Microsoft QuickBASIC 4.0: BASIC Language Reference" manual for
versions 4.00 and 4.00b, as follows:

   Because BASIC may rearrange arithmetic expressions for greater
   efficiency, avoid using FUNCTION procedures that change program
   variables in arithmetic expressions. Also avoid using FUNCTION
   procedures that perform I/O in I/O statements. Using FUNCTION
   procedures that perform graphics operations in graphics statements
   may also cause side effects.

The same restriction is mentioned on Page 201 of the "Microsoft BASIC
Compiler 6.0: BASIC Language Reference" for versions 6.00 and 6.00b
for MS OS/2 and MS-DOS. It is also mentioned on Page 146 of the
"Microsoft BASIC 7.0: Language Reference" manual.

Please note that user-defined functions defined with the DEF FN
statement do not have the above restrictions.

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