while循环行为，如何计算表达式

Question

If the following line of code causes php to consume 100% of the cpu time

 while(true){}

then why should the following code not do the same? after all, !feof($fp) is just a boolean expression, and when evaluating as true, it uses no perceivable cpu time at all.

 $fp = stream_socket_client($remote_socket);
 while(!feof($fp)){}

Answer 1

This is about how much work goes on in the loop before the loop condition is evaluated again, and for how long that condition will remain true.

while(true){} Nothing to evaluate and forever. So 100%

While(true) 
{
  // Wait 1 second for a key press
  // Display another '.'
}

loop still runs forever, but there's a 'pause' of one second every execution of the loop.

Your example given eof is and remains true it will never exit, but checking eof takes some time, so it won't be a 100%, be fairly close though I should think...