Read and write /dev/ttya?

[Holger Veit]

montnaro at spyder.crd.ge.com (Skip Montanaro) writes:


[...]
>All communication with the device is printable ASCII, so for simplicity I'm
>just using stdio. I'm successful writing to the device. (This I know because
      ^^^^^^^^^^^^
>the MiniVAS and the VTR do the anticipated things.) However, I can't seem to
>read the response stream. Here's what I'm doing in effect (sans declarations
>and error checking):

>	f = fopen("/dev/ttya", "r+");
>	fprintf(f, "VSG");
>	fflush(f);

>	ch = getc(f);

>	if (ch != 'I') ...

>The getc() just hangs. What am I doing wrong?

stdio does input and output buffering. If your answering device does not
deliver a Carriage return as a block limiter, your getc() call will wait
forever. Try including 
	setbuf(f,NULL);	
as described in setbuf(3V) after your fopen statement, this should switch
to unbuffered I/O.

Holger Veit


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