php开发之时间和日期的应用
1，比较两个日期的大小
比较两个日期的大小，首先是将日期转换为时间戳，然后对时间戳进行比较。
具体示例代码如下：
<code class=" hljs xml"><span class="php"><span class="hljs-preprocessor"><?php</span><span class="hljs-variable">$time1</span> =date(<span class="hljs-string">"Y-m-d H:i:s"</span>);<span class="hljs-variable">$time2</span> =<span class="hljs-string">"2009-12-9 4:40:12"</span>;<span class="hljs-keyword">echo</span> <span class="hljs-string">"时间变量\$time1 的时间为："</span>.<span class="hljs-variable">$time1</span>.<span class="hljs-string">"\n"</span>;<span class="hljs-keyword">echo</span> <span class="hljs-string">"时间变量\$time2 的时间为："</span>.<span class="hljs-variable">$time2</span>.<span class="hljs-string">"\n"</span>;<span class="hljs-keyword">if</span>(Strtotime(<span class="hljs-variable">$time1</span>)-strtotime(<span class="hljs-variable">$time2</span>)<<span class="hljs-number">0</span>){ <span class="hljs-keyword">echo</span> <span class="hljs-string">"\$time1早于\$time2"</span>;}<span class="hljs-keyword">else</span>{ <span class="hljs-keyword">echo</span> <span class="hljs-string">"\$time2早于\$time1"</span>;}<span class="hljs-preprocessor">?></span></span></code>运行结果如下： 
2，实现页面脚本运行的时间
这里主要使用microtime()函数来实现，该函数返回当前UNIX时间戳和微秒数。返回格式为msec sec的字符串。其中sec为当前的UNIX时间戳，msec为微秒数。
语法格式如下：
string microtime(void)
示例代码如下：
<code class=" hljs xml"><span class="php"><span class="hljs-preprocessor"><?php</span><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">run_time</span><span class="hljs-params">()</span>{</span> <span class="hljs-keyword">list</span>(<span class="hljs-variable">$msec</span>,<span class="hljs-variable">$sec</span>) =explode(<span class="hljs-string">" "</span>,microtime()); <span class="hljs-comment">//使用explode()函数返回两个变量</span> <span class="hljs-keyword">return</span>((float)<span class="hljs-variable">$msec</span> + (float)<span class="hljs-variable">$sec</span>); <span class="hljs-comment">//返回两个变量的和</span>}<span class="hljs-variable">$start</span> =run_time(); <span class="hljs-comment">//第一次运行run_time()函数</span><span class="hljs-keyword">for</span>(<span class="hljs-variable">$i</span>=<span class="hljs-number">0</span>;<span class="hljs-variable">$i</span><<span class="hljs-number">100000</span>;<span class="hljs-variable">$i</span>++){}<span class="hljs-variable">$end</span> =run_time(); <span class="hljs-comment">//再一次运行run_time()函数</span><span class="hljs-keyword">echo</span> <span class="hljs-string">"运行的时间："</span>.(<span class="hljs-variable">$end</span>-<span class="hljs-variable">$start</span>).<span class="hljs-string">"\n"</span>;<span class="hljs-preprocessor">?></span></span></code>
