Q58411: C Char Parameters Passed from BASIC as 2-Byte Parameters

Article: Q58411
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900126-85 B_BasicCom S_C S_QuickC BAS2C | mspl13_basic
Last Modified: 9-FEB-1990

Microsoft C uses 2 bytes when passing single-byte parameters;
therefore, to pass a single-byte data item by value between C and
BASIC, the BASIC parameter must be DECLAREd as an INTEGER.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
and 4.50 for MS-DOS, to Microsoft BASIC Compiler Versions 6.00 and
6.00b for MS-DOS and MS OS/2, to Microsoft BASIC Professional
Development System (PDS) Version 7.00 for MS-DOS and MS OS/2, to
Microsoft QuickC Versions 2.00 and 2.01 for MS-DOS, and to Microsoft C
Compiler Versions 5.00 and 5.10 for MS-DOS and MS OS/2.

The two programs below demonstrate passing a character by value from
BASIC to C.

To run the programs, do the following:

1. Compile as follows, depending on which language you are using:

   a. Compile in BASIC as follows:

         BC testb ;

   b. For Microsoft C Versions 5.00 and 5.10, compile as follows:

         CL -c -AL test.c ;

   c. For Microsoft QuickC, compile as follows:

         QCL -c -AL test.c ;

2. LINK with the following line:

      LINK /NOE testb+test ;

The following program, TESTB.BAS, illustrates passing characters from
BASIC to C by using the ASCII values and DECLAREing the C char
parameter with BYVAL var AS INTEGER:

   DECLARE SUB test CDECL (BYVAL a%, BYVAL b%)
   CALL test(ASC("A"), ASC("B"))
   END

TEST.C is as follows:

   void test(char a, char b)
     {
     printf("%c %c\n",a,b);
     }

When compiled and run, TESTB.EXE displays the following:

   A B

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