为什么从字符串到整数的类型转换总是返回“0”？

Question

I'm writing an AJAX chat script and I'm integrating a system to parse the time (basically like BBCode). The problem is, when I try casting the time (UNIX timestamp) to an integer for use with date(), it always returns "0". The code I am using to find and replace is below. I've also added a sample of what I'm trying to parse

$out = preg_replace("/\[time\](.*)\[\/time\]/i",date("c",(int)"$1",$out);

Sample:

<b>GtoXic</b>: [time]1342129366[/time]

Answer 1

Because what you are actually casting to an integer is the literal string $1, and converting a string to an integer works in the following way:

• If the start of the string is a valid numeric representation, use that until we come across a character incompatible with that format
• Otherwise return zero

In order to get this to work, you would use preg_replace_callback():

$output = preg_replace_callback("/#\[time\](.*)\[/time\]#i", function ($matches) {
  return date("c", $matches[1]);
}, $input);

The (int) cast is actually unnecessary, PHP will automatically handle this when you pass the value to a function that expects an integer.