Re: result=read(fd,buffer,200);

[Jan-Benedict Glaw <jbglaw@lug-owl.de>]

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On Tue, 2004-07-20 17:41:42 +0200, Gerald Emig <gme@emig-software.de>
wrote in message <20040720174142.7b8b6525@emig4.heisch.inka.de>:
> According to the documentation provided in info:libc, read 
> returns the number of character it actually has read.
> Especially if you are using serial ports, the amount read is often fewer
> as you expected.

That's a general thing to keep in mind.

Additionally, keep in mind that c_cc[VMIN] will control how long to
wait, too...

> Additionally, checking errno is stronly recommended.

As always:)

> Use something like the following to read exactly 200 chars:
> 
> 
> int read_amount (int iwantread)

This int should have been size_t.

> {
> 	int readpointer, fetch;

...and fetch needs to be ssize_t.

> readpointer=0;
> while (iwantread>0) {
> 	fetch=read (fd,&buffer[readpointer],iwantread);
> 	if (fetch >= 0) {
> 		readpointer += fetch;
> 		iwantread -= fetch;
> 	} else 	if ((errno!=EINTR) && (errno!=EAGAIN)) return -1;
> 	}
> 	return iwantread; // should be 0 on success
> }

MfG, JBG

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