Technical data

Programming Example 4
Programmer’s Guide 35
viScanf(viN9342C, "%t", &buf);
/*Print results */
printf("Instrument identification string: %s\n",
buf);
/* Close the sessions */
viClose(viN9342C);
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.