Q47348: Example of Passing Fixed-Length Strings from C to BASIC

Article: Q47348
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890711-46 B_BasicCom S_C S_QuickC | mspl13_basic
Last Modified: 28-DEC-1989

To pass a string from Microsoft C to compiled BASIC, the string must
originate in BASIC. A fixed-length string works best for this purpose.
In the C module, you can modify the string, and BASIC will recognize
this modification because BASIC is referencing the address of the
string.

This information about interlanguage calling applies to 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, and to Microsoft BASIC
PDS Version 7.00 for MS-DOS and MS OS/2.

For more information about passing other types of parameters between
BASIC and C, and a list of which BASIC and C versions are compatible
with each other, query in the Software/Data Library on the following
word:

   BAS2C

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

The following program is an example of passing a fixed-length string
from C to BASIC (where the string is first allocated in BASIC). Please
note that the C module needs to use the medium memory model.

Compile Steps
-------------

   BC callc.bas /o;

   cl /c /AM stringf.c

Link Step
---------

   LINK callc+stringf /nod /noe ,,,bcom45+mlibce;

For BASIC PDS 7.00, use the following link step:

   LINK callc+stringf /nod /noe ,,,bcl70enr.lib+mlibce.lib;

BASIC Program
-------------

'CALLC.BAS
DECLARE SUB StringFar CDECL (_
            BYVAL p1o AS INTEGER,_
            BYVAL p1s AS INTEGER,_
            SEG p3 AS INTEGER)
CLS
DIM array AS STRING * 15
array = "This is a test" + CHR$(0)
CALL StringFar(VARPTR(array), VARSEG(array), LEN(array))
LOCATE 20,20
PRINT array
END

C Program
---------

/* stringf.c */
#include <stdio.h>
void StringFar(a,len)
   char far *a;
    int *len;
 {
    int i;
    printf("The string is : %s \n\n",a);
    printf(" Index       Value       Character\n");
    for (i=0;i < *len; i++)
     {
         printf("  %2d       %3d      %c\n",i,a[i],a[i]);
     };

    /* This loop shows that the string can be modified.
       It fills the string with the '@' character.
    */
    for (i=10;i < *len; i++)
      {
         a[i]=64;
      }
 }

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