5.8 Piped and Local Records

Piped record header files allow application programs to read signals from the standard input, or write them to the standard output. Record ‘8’ specifies 8-bit format, a 10-bit ADC, zero ADC offset, and two signals sampled at 250 Hz, both of which are to be acquired from the standard input, or written to the standard output. Record ‘16’ specifies 16-bit format and a 12-bit ADC, and is otherwise identical to record ‘8’. ADCs from several manufacturers can produce output in the format specified by record ‘16’; thus such output can be piped directly into an application program using record ‘16’. Signal files in AHA format also match these specifications. Piped records for reading or writing other numbers of signals are provided in the ‘pipe’ subdirectory of the system-wide database directory; they are named ‘pipe/8xn’ and ‘pipe/16xn’, where n is the number of signals (n = 1, 2, …, 16; piped record header files can be created with larger numbers of signals (use the existing files as a model).

Application programs may also read or write signal files in the current directory using local record header files. Record ‘16l’ (“one-six-ell”) specifies up to sixteen format 16 files, and record ‘8l’ (“eight-ell”) specifies up to sixteen format 8 files, named ‘data0’, ‘data1’, ‘data2’, …, ‘datan’ in the current directory. When opened using isigopen or wfdbinit, these signal files will be readable by getvec as signals 0, 1, 2, … 16 respectively. These files should be created by the user, with the use of putvec. It is necessary to create only as many signal files as will be used; if, for example, only one signal is needed, only ‘data0’ need be created.