Strange issue with PHP's microtime

Question

I'm trying to use php's microtime() to benchmark how long two loops in my code take, to see which one runs faster. Here's my code:

$now = microtime();

//loop1  here

$elapsed = microtime() - $now;
echo "Elapsed: $elapsed <br />";

When I run this for one loop, I get the result in negative numbers, something like:

Elapsed: -0.120572 

This is strange, since microtime() should always be bigger than its value a few microseconds earlier?

For the second loop, the value is always positive:

Elapsed: 0.005483 

What's going on here?

Answer 1

根据http://au1.php.net/manual/en/function.microtime.php使用microtime(true) as false 将 microtime 作为字符串返回，并且您在字符串上执行数学运算而不是作为数字..