Adding other Win32 Functions

If a program requires a Win32 function (a function defined in one of Windows' system DLLs), and the function is not provided by Rtt32.lib or Rtt32dll.dll, the function must be supplied by your program.

The following steps are required:

Create a source file for the new function.
Declare the function exactly as it is defined in the Windows header file.
Implement the function.
Implement a call stub (not required for Borland C/C++).

Example:

Suppose you need the function CharUpperA, which is not included in RTTarget-32's library. The following source code could be used to implement it:

#define _USER32_        // required by Microsoft C 
#define _KERNEL32_      // to prevent importing this function 
#include <windows.h> 

WINUSERAPI LPSTR WINAPI CharUpperA(LPSTR lpsz) 
{ 
   LPSTR p = lpsz; 
   while (*p) 
   { 
      if (*p >= 'a' && *p <= 'z') 
         *p -= 'a' - 'A'; 
      p++; 
   } 
   return lpsz; 
}

This file should be compiled and linked with your program.

For Microsoft C, an assembler call stub is also required:

.386 

EXTRN  _CharUpperA@4:near 
PUBLIC __imp__CharUpperA@4 
PUBLIC _CharUpperA 

_TEXT SEGMENT DWORD USE32 PUBLIC 'CODE' 

ASSUME CS:_TEXT, DS:_TEXT 

__imp__CharUpperA@4 DD offset _CharUpperA@4 
_CharUpperA: JMP _CharUpperA@4 

_TEXT ENDS 

END

The numeric value following the at sign (@) represents the number of bytes the function expects as parameters. The value is decimal and is usually four times the number of parameters. Function CharUpperA requires just one parameter, so 4 bytes are pushed onto the stack.

The call stub must be assembled and linked to the program.

As an alternative to a call stub, it is also possible to use RTLoc's Link command. In this case, the import table's call stub is used.

Left Win32 Emulation

Win32 API Function Cross Reference