用vc6编程实现gpib通信

我是用Agilent VISA程序库，按照visa手册对vc进行设置，粘了一个实现IDN？功能的程序，编译链接没问题，但执行试并没有得到仪器名称。仪器在visa assistant中已经查到并能实现idn？功能。程序如下：
/*idn.c
  This example program queries a GPIB device for an identification string
  and prints the results. Note that you must change the address. */

#include
#include

void main () {

  ViSession defaultRM, vi;
  char buf [256] = {0};


  /* Open session to GPIB device at address 22 */
  viOpenDefaultRM (&defaultRM);
  viOpen (defaultRM, "GPIB0::22::INSTR", VI_NULL,VI_NULL, &vi);

  /* Initialize device */
  viPrintf (vi, "*RSTn");

  /* Send an *IDN? string to the device */
  viPrintf (vi, "*IDN?n");

  /* Read results */
  viScanf (vi, "%t", &buf);

  /* Print results */
  printf ("Instrument id string: %sn", buf);

  /* Close session */
  viClose (vi);
  viClose (defaultRM);
}