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Q30271: LINK QB & C "Unresolved Externals"; How to Use LINK /NOE, /NOD

Article: Q30271
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom S_C S_QuickC | mspl13_basic
Last Modified: 13-MAR-1990

The following article explains how to compile and link the example of
linking QuickBASIC to Microsoft C shown on Page 391 of the "Microsoft
QuickBASIC 4.0: BASIC Language Reference" manual for Versions 4.00 and
4.00b, and Page 391 of the "Microsoft BASIC Compiler 6.0: BASIC
Language Reference" manual for Microsoft BASIC Compiler Versions 6.00
and 6.00b for MS-DOS and MS OS/2.

This article also explains how to use the LINK /NOE and /NOD options
to eliminate error messages when linking to C.

When linking BASIC to C (or to other Microsoft languages), please note
the following information about using the LINK /NOE and /NOD options:

1. Notes for using LINK /NOE Option are as follows:

   The LINK /NOE option is required for interlanguage calling to
   eliminate the following error message:

      xx.LIB : error L2044: __xxxxx : symbol multiply defined, use /NOE

   The Microsoft language libraries, such as LLIBCE.LIB from C and
   BRUN40.LIB from QuickBASIC, contain some of the same routines;
   thus, they require LINK /NOE.

   If you still get a "symbol multiply defined" message after using
   the LINK /NOE option, then the multiply defined symbols in your
   source code need to be renamed, recompiled, and relinked.

   The /NOE option is documented only in the README.DOC file on a disk
   in QuickBASIC 4.00 and 4.00b and in BASIC compiler 6.00 and 6.00b.
   In QuickBASIC Version 4.50, /NOE is documented on Page 365 of the
   "Microsoft QuickBASIC 4.5: Programming in BASIC" manual.

2. Notes for using LINK /NOD Option are as follows:

   Note that an .OBJ file compiled with QuickBASIC 4.00, 4.00b, or
   4.50, or C 5.00 or 5.10 contains information telling the linker
   what .LIB file to look for at link time.

   If you use the LINK /NOD option, you are telling the linker not to
   search any specified library in the .OBJ file to resolve external
   references. Thus, if you use the /NOD option, you must explicitly
   specify the name of the .LIB language libraries for both C and
   QuickBASIC in the LINK command (even if the .LIB library has a path
   set to it with SET LIB=path). If you do not, LINK.EXE will give the
   following error:

      LINK : error L2029: Unresolved Externals

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

The following steps describe how to compile and link the code example
shown at the bottom of this article (taken from Page 391 of the
BASIC language reference manuals):

1. Compile cf.bas and cfunc.c (shown farther below) as follows:

      BC CF.BAS;
      CL /C /AL CFUNC.C

   You may also use the C medium-memory model: CL /C /AM CFUNC.C. This
   example uses CL.EXE from Microsoft C Versions 5.00 and 5.10.

2. Type SET at the DOS command line to make sure that you issued a
   statement similar to "SET LIB=C:\QB.400;C:\C.500" to tell LINK.EXE
   where to look for .LIB files at link time.

3. Link the BASIC and C routines, specifying the BASIC routine first
   and using LINK.EXE Version 3.61 or later:

      LINK CF.OBJ+CFUNC.OBJ/NOE;

CF.BAS
------

   REM  BASIC routine cf.bas:
   DEFINT A-Z
   DECLARE SUB cfunc CDECL (BYVAL x AS INTEGER)
   beforecall = SETMEM(-2048)
   cfunc (1024)
   aftercall = SETMEM(3500)
   IF aftercall <= beforecall THEN PRINT "memory not reallocated."
   END

CFUNC.C
-------

   /*  C routine cfunc.c:    */
   void far cfunc(bytes)
   int bytes;
   {
    char *malloc();
    char *workspace;
    workspace=malloc((unsigned) bytes);
    free(workspace);
   }

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