PHP中isset与array_key_exists的区别实例分析

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：

<?phpfunction 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（$test_arr["aa"]））;echo "
";echo "isset bb is ";var_dump（isset（$test_arr["bb"]））;echo "
";echo "isset cc is ";var_dump（isset（$test_arr["cc"]））;echo "
";echo "isset dd is ";var_dump（isset（$test_arr["cc"]））;echo "
";echo "isset none is ";var_dump（isset（$test_arr["none"]））;echo "
";echo "key_exist aa is ";var_dump（array_key_exists（"aa",$test_arr））;echo "
";echo "key_exist bb is ";var_dump（array_key_exists（"bb",$test_arr））;echo "
";echo "key_exist cc is ";var_dump（array_key_exists（"cc",$test_arr））;echo "
";echo "key_exist dd is ";var_dump（array_key_exists（"dd",$test_arr））;echo "
";echo "key_exist none is ";var_dump（array_key_exists（"none",$test_arr））;echo "
";$time_start = microtime_float（）;for（$i=0;$i<100;$i++）{isset（$test_arr["aa"]）;}$time_end = microtime_float（）;$time = $time_end - $time_start;echo "isset 100 is $time
";for（$i=0;$i<10000;$i++）{isset（$test_arr["aa"]）;}$time_end = microtime_float（）;$time = $time_end - $time_start;echo "isset 10000 is $time
";for（$i=0;$i<1000000;$i++）{isset（$test_arr["aa"]）;}$time_end = microtime_float（）;$time = $time_end - $time_start;echo "isset 1000000 is $time
";//++++++++++++++++++++++++++++++$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 $time
";for（$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 $time
";for（$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
";

希望本文所述对大家的php程序设计有所帮助。