再看那柔弱的柳树吧,在寒冬余威尚盛时节,就早早苏醒过来,望着冰冻的河面,迎着凛冽的寒风,它微微察觉出一丝春意,于是,不顾一切地率先吐翠,淡淡地披起娇黄嫩绿的新装。沿河望去,枝梢间烟纱雾彀,一片生机,这情景仿佛一首动人的歌,一首热烈向往春天的歌,一首报告春的信息的歌,一首表达美好信念的歌。我在想:既然迎春花被人称作报春花,那么,柳树可不可以叫作报春树呢春来了,万千柳枝在春风中袅袅舞动。柳树是热爱春天的,春天也是热爱柳树的。
本文实例讲述了PHP中isset与array_key_exists的区别。分享给大家供大家参考。具体分析如下:
1.对于数组值的判断不同,对于值为null或''或false,isset返回false,array_key_exists返回true;
2. 执行效率不同,isset是内建运算符,array_key_exists是php内置函数,isset要快一些。请参考:PHP 函数实现原理及性能分析
3.当用isset访问一个不存在索引数组值时,不会引起一个E_NOTICE的php错误消息;
4.array_key_exists 会调用get_defined_vars判断数组变量是否存在,isset不用;
测试代码:
<?php function microtime_float() { list($usec, $sec) = explode(" ", microtime()); return ((float)$usec + (float)$sec); } $test_arr['aa']='dd'; $test_arr['bb']=''; $test_arr['cc']=NULL; $test_arr['dd']=false; $test_arr= array('aa'=>'dd','bb'=>'','cc'=>null,'dd'=>false); echo "isset aa is ";var_dump(isset($test_arr['aa']));echo "\n"; echo "isset bb is ";var_dump(isset($test_arr['bb']));echo "\n"; echo "isset cc is ";var_dump(isset($test_arr['cc']));echo "\n"; echo "isset dd is ";var_dump(isset($test_arr['cc']));echo "\n"; echo "isset none is ";var_dump(isset($test_arr['none']));echo "\n"; echo "key_exist aa is ";var_dump(array_key_exists('aa',$test_arr));echo "\n"; echo "key_exist bb is ";var_dump(array_key_exists('bb',$test_arr));echo "\n"; echo "key_exist cc is ";var_dump(array_key_exists('cc',$test_arr));echo "\n"; echo "key_exist dd is ";var_dump(array_key_exists('dd',$test_arr));echo "\n"; echo "key_exist none is ";var_dump(array_key_exists('none',$test_arr));echo "\n"; $time_start = microtime_float(); for($i=0;$i<100;$i++){ isset($test_arr['aa']); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "isset 100 is $time\n"; for($i=0;$i<10000;$i++){ isset($test_arr['aa']); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "isset 10000 is $time\n"; for($i=0;$i<1000000;$i++){ isset($test_arr['aa']); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "isset 1000000 is $time\n"; //++++++++++++++++++++++++++++++ $time_start = microtime_float(); for($i=0;$i<100;$i++){ array_key_exists('aa',$test_arr); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "array_key_exists 100 is $time\n"; for($i=0;$i<10000;$i++){ array_key_exists('aa',$test_arr); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "array_key_exists 10000 is $time\n"; for($i=0;$i<1000000;$i++){ array_key_exists('aa',$test_arr); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "array_key_exists 1000000 is $time\n";
希望本文所述对大家的php程序设计有所帮助。
到此这篇关于PHP中isset与array_key_exists的区别实例分析就介绍到这了。无论你有多少朋友,不能少了书这个诤友。更多相关PHP中isset与array_key_exists的区别实例分析内容请查看相关栏目,小编编辑不易,再次感谢大家的支持!