Example of Passing Strings from C to Basic (48207)

SUMMARY

The two programs below demonstrate how Microsoft C can create and pass both fixed-length and variable-length strings to Microsoft Basic.

This information about interlanguage calling applies to QuickBasic versions 4.00, 4.00b, 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 Professional Development System (PDS) versions 7.00 and 7.10 for MS-DOS and MS OS/2.

For Basic PDS 7.00 and 7.10, this example works only with near strings. If you are using far strings (BC /Fs compile switch or in QBX.EXE), you must use the string-manipulation routines provided with Basic PDS 7.00 and 7.10 to change variable-length strings (StringAssign, StringRelease, StringAddress, and StringLength). For more information about using far strings, see Chapter 13 of the "Microsoft Basic 7.0: Programmer's Guide" for versions 7.00 and 7.10.

MORE INFORMATION

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, search in the Microsoft Knowledge Base using the following word:

BAS2C

Code Example

The following Basic program is BSUB.BAS, which invokes a C routine that creates two strings and passes them to a Basic subroutine. The Basic subroutine prints out the string (and the string's length) received from the C routine.

   DECLARE SUB CSUB CDECL()
   TYPE fixstringtype        ' Must use type to pass fixed-length string
      B AS STRING * 26       '  in parameter list.
   END TYPE
   CALL CSUB
   END

   SUB BASSUB(A$, B AS fixstringtype)  ' Subroutine called from C
      PRINT A$
      PRINT LEN(A$)
      PRINT B.B
      PRINT LEN(B.B)
   END SUB

The following program is CSUB.C, which builds a string descriptor that is passed to a called Basic subroutine:

#include <string.h>
struct stringdesc
       {
        int length;       /* string length */ 
        char *string;     /* near address of the string */ 
       };
extern void pascal bassub(struct stringdesc *basstring,
                          char *basfixstring);
struct stringdesc *std;
char thesecondstring[26];

void csub()
{                                         /* create the strings */ 
   std->length = 18;
   strcpy(std->string, "This is the string");
   strcpy(thesecondstring, "This is the second string");
   bassub(std, thesecondstring);          /* call Basic subroutine */ 
}

To demonstrate these programs from an .EXE program, compile and link as follows:

   BC BSUB.BAS;
   CL /c /AM CSUB.C;
   LINK /NOE BSUB CSUB;

BSUB.EXE produces the following output:

   This is the string
   18
   This is the second string
   26