Example 5: Reading Signal Specifications

This program reads the signal specifications of the record named as its argument:

 1  #include <stdio.h>
 2  #include <ecg/db.h>
 3
 4  main(argc, argv)
 5  int argc;
 6  char *argv[];
 7  {
 8      static DB_Siginfo s[DB_MAXSIG];
 9      int i, nsig;
10
11      if (argc < 2) {
12          fprintf(stderr, "usage: %s record\n", argv[0]);
13          exit(1);
14      }
15      nsig = isigopen(argv[1], s, DB_MAXSIG);
16      if (nsig < 1) exit(2);
17      printf("Record %s\n", argv[1]);
18      printf("Starting time: %s\n", timstr(0L));
19      printf("Sampling frequency: %g Hz\n", sampfreq(argv[1]));
20      printf("%d signals\n", nsig);
21      for (i = 0; i < nsig; i++) {
22          printf("Group %d, Signal %d:\n", s[i].group, i);
23          printf(" File: %s\n", s[i].fname);
24          printf(" Description: %s\n", s[i].desc);
25          printf(" Gain: ");
26          if (s[i].gain == 0.)
27              printf("uncalibrated; assume %g", DEFGAIN);
28          else printf("%g", s[i].gain);
29          printf(" adu/%s\n", s[i].units ? s[i].units : "mV");
30          printf(" Initial value: %d\n", s[i].initval);
31          printf(" Storage format: %d\n", s[i].fmt);
32          printf(" I/O: ");
33          if (s[i].bsize == 0) printf("can be unbuffered\n");
34          else printf("%d-byte blocks\n", s[i].bsize);
35          printf(" ADC resolution: %d bits\n", s[i].adcres);
36          printf(" ADC zero: %d\n", s[i].adczero);
37          if (s[i].nsamp > 0L) {
38              printf(" Length: %s (%ld sample intervals)\n",
39                     timstr(s[i].nsamp), s[i].nsamp);
40              printf(" Checksum: %d\n", s[i].cksum);
41          }
42          else printf(" Length undefined\n");
43      }
44      exit(0);
45  }

Notes:

Line 8:

There might be as many as DB_MAXSIG signals, so we allocate enough DB_Siginfo objects to accommodate them all.

Line 15:

The command-line argument, argv[1], is the record name. The number of readable signals is nsig. This program will give specifications for each of them, but not for any signals that are named in the `header' file but are not readable. If nsig < 1, isigopen will print an error message; in this case the program can't do anything useful, so it exits.

Line 18:

Invoking timstr with an argument of zero (here written `0L' to emphasize to the compiler that the argument is a long integer) will obtain the starting time of the record. If no starting time is defined, timstr will return "0:00:00".

Lines 25--28:

Notice how a zero value for gain is interpreted.

Line 29:

If the units field is NULL, the physical units are assumed to be millivolts ("mV").

Lines 32--34:

If bsize is zero, I/O can be performed in blocks of any reasonable size; otherwise it must be performed in blocks of exactly the specified bsize.

Lines 37--42:

If the length of the record is defined, it is printed in both hours, minutes, and seconds, and in sample intervals. Since the argument of timstr in line 39 is positive, it is interpreted as a time interval. The checksum is defined only if the record length is defined.

Go to the first, previous, next, last section, table of contents.