PHP 微时间的奇怪问题

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..