Testing select on various platforms...

darwin.txt

Output on OS X:

ret = 6
fh1 read
fh2 read
fh1 write
fh2 write
fh1 error
fh2 error

debian.txt

Output on Linux:

ret = 4
fh1 read
fh2 read
fh1 write
fh2 write

select.c

#include <sys/select.h>
#include <fcntl.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
	int fh1 = open("README", O_RDONLY);
	int fh2 = open("README2", O_WRONLY | O_CREAT, 0666);

	fd_set rdset, wrset, erset;
	FD_ZERO(&rdset);
	FD_SET(fh1, &rdset);
	FD_SET(fh2, &rdset);
	FD_ZERO(&wrset);
	FD_SET(fh1, &wrset);
	FD_SET(fh2, &wrset);
	FD_ZERO(&erset);
	FD_SET(fh1, &erset);
	FD_SET(fh2, &erset);

	struct timeval timeout;
	timeout.tv_sec = 1;

	int nfds = fh1 > fh2 ? fh1 : fh2;
	int ret = select(nfds+1, &rdset, &wrset, &erset, &timeout);

	printf("ret = %d\n", ret);
	if( FD_ISSET(fh1, &rdset) ) printf("fh1 read\n");
	if( FD_ISSET(fh2, &rdset) ) printf("fh2 read\n");
	if( FD_ISSET(fh1, &wrset) ) printf("fh1 write\n");
	if( FD_ISSET(fh2, &wrset) ) printf("fh2 write\n");
	if( FD_ISSET(fh1, &erset) ) printf("fh1 error\n");
	if( FD_ISSET(fh2, &erset) ) printf("fh2 error\n");

	return 0;
}