stdlib issue for CryptoSys API

This solves two issues for C and C++ programmers with CryptoSys API:

Why won't it compile with Visual C++ 2005 Express?
'Unresolved external ... referenced from xxx.OBJ' error with Borland C++

Symptoms

In Borland C++:

[Linker Error] Unresolved external '__stdcall API_Function(...) referenced from xxx.OBJ

Error: Unresolved external '_API_Function' referenced from xxx.OBJ'

In Visual C++ 2005 Express:

error LNK2019: unresolved external symbol _API_Function referenced in function _main

fatal error C1083: Cannot open include file: 'windows.h': No such file or directory

The problem

The C include file diCryptoSys.h for version 3.2.0 of CryptoSys API contains the following at lines 19-27:-

/* We only need windows.h for _stdcall convention */
#ifdef WIN32
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#else
/* Ignore for Linux */
#define _stdcall
#endif

The preprocessor #ifdef directive was introduced in version 3.2 so we could use the same include file for the Linux distribution.

The first error is that this should have read

/* We only need windows.h for __stdcall convention */
#if defined(_WIN32) || defined(WIN32)
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#else
/* Ignore for Linux */
#define _stdcall
#endif

The preprocessor constant WIN32 is defined by default in earlier versions of MSVC++ but not in Borland C++ or in Visual C++ 2005 Express (MSVC++8). Hence the "unresolved external" problems with those compilers.

In the manual we suggested one solution for Visual C++ 2005 Express (MSVC++8):

Set the Calling Convention to __stdcall (/Gz) using Project>Properties>Configuration Properties>Advanced>Calling Convention.

This is now redundant and can be ignored. However, users who had downloaded the vanilla version of Visual C++ 2005 Express would also end up with the "missing windows.h" problem (see below on how to solve).

The Solution

In fact, in both MSVC and Borland, you do not need the reference to windows.h at all. _stdcall (or __stdcall) is a standard keyword for both compilers. You can delete all the 8 lines above from the CryptoSys .h include files and both the "unresolved external" and "missing windows.h" problems go away.

A better, Linux-compatible solution is to replace the 8 lines above with:

/* __stdcall convention required for Win32 DLL only */
#if defined(unix) || defined (linux) || defined(__linux)
#define _stdcall
#endif

Remarks

This issue has been fixed in version 4.0
Thanks to Farjad Farid for bringing this problem with Borland C++ to our attention.
We've been working with programming interfaces to Windows DLLs since the 1990s and we never realised that you don't need to include <windows.h> at all to get the "_stdcall" interface to work. Just goes to show, eh? Thanks are due, it seems, to the makers of Visual C++ 2005 Express for helping us eventually find this out.
The "missing windows.h" problem in Visual C++ 2005 Express can be solved by downloading the latest Windows SDK and adding a new entry for "Include files" in Tools>Options>VC++ Directories. In our system this is C:\Program Files\Microsoft Platform SDK for Windows Server 2003 R2\Include. Thanks to josh1billion for this.

This page last updated 1 January 2008

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