Creating a HLLAPI Program

If you wish to develop new applications that will communicate with the 3270 emulator, we suggest that you use the WinHLLAPI interface. For almost all of the WinHLLAPI program functions to work, you need to be connected to a 3270 host.

To help you get started with HLLAPI development, two sample HLLAPI applications and the full set of HLLAPI specifications were optionally installed on your PC when the QWS3270 Secure application was installed. They are located in the samples sub-directory of the installation directory. One sample is written in Visual Basic, the other using the C programming language. The development files include:

HLLAPI.txt/readme.txt	Read me file
modDLLTest.bas	Visual Basic module file
DLL_Sample.frm	Visual Basic form file
frmAbout.frm	Visual Basic form file
frmQuestion.frm	Visual Basic form file
frmText.frm	Visual Basic form file
QWS_DDL_Sample.vbp	Visual Basic project file

C_Sample_app.dsw	VC6 workspace file
C_Sample_app.dsp	VC6 project file
C_Sample_app.rc	Resource compiler file
main.c	C source code
main.h	C header file
resource.h	Resource header file

whllapi.h	C header file
whllapi.dll	32-bit dynamic link library
whllapi.lib	lib file for inclusion in VC projects

C_Sample_app.exe	Compiled C executable
DLL_Sample.exe	Compiled VB executable

In order to use the HLLAPI interface, you will also need to have the whllapi.dll installed in your search path. QWS3270 Secure installs the file by default into its own directory.

There are certain restrictions with WinHLLAPI programming that should be noted.

Byte Ordering

The implemented Intel byte ordering is like the DEC VAX, and so it differs from the Internet and 68000-type processor byte ordering. Make sure that your programming considers this byte ordering.

Deviation from IBM EHLLAPI

There are a few instances where WinHLLAPI differs slightly from the IBM EHLLAPI standard. This is due to the graphical nature of the Windows environment, and how it differs from other HLLAPI platforms.

Pointers

All pointers used by applications with WinHLLAPI should be defined as FAR. In Visual Basic parameters should be passed ByRef.

A copy of the HLLAPI specifications has also been installed in the samples directory. The file is called winhlapi.hlp and is in form of a Windows help file.