Agilent Technologies E4406A VSA manual Including the Visa Declarations File, Opening a Session

Programming Fundamentals

C Programming Using VTL

viClose (vi); viClose (defaultRM);

}

Including the VISA Declarations File

For C and C++ programs, you must include the visa.h header file at the beginning of every file that contains VTL function calls:

#include “visa.h”

This header file contains the VISA function prototypes and the definitions for all VISA constants and error codes. The visa.h header file includes the visatype.h header file.

The visatype.h header file defines most of the VISA types. The VISA types are used throughout VTL to specify data types used in the functions. For example, the viOpenDefaultRM function requires a pointer to a parameter of type ViSession. If you find ViSession in the visatype.h header file, you will find that ViSession is eventually typed as an unsigned long.

Opening a Session

A session is a channel of communication. Sessions must first be opened on the default resource manager, and then for each device you will be using. The following is a summary of sessions that can be opened:

•A resource manager session is used to initialize the VISA system. It is a parent session that knows about all the opened sessions. A resource manager session must be opened before any other session can be opened.

•A device session is used to communicate with a device on an interface. A device session must be opened for each device you will be using. When you use a device session you can communicate without worrying about the type of interface to which it si connected. This insulation makes applications more robust and portable across interfaces. Typically a device is an instrument, but could be a computer, a plotter, or a printer.

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