《PHP應(yīng)用：PHP中isset與array_key_exists的區(qū)別實(shí)例分析》要點(diǎn)：
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PHP教程本文實(shí)例講述了PHP中isset與array_key_exists的區(qū)別.分享給大家供大家參考.具體分析如下：
PHP教程1.對(duì)于數(shù)組值的判斷不同,對(duì)于值為null或''或false,isset返回false,array_key_exists返回true；
PHP教程2. 執(zhí)行效率不同,isset是內(nèi)建運(yùn)算符,array_key_exists是php內(nèi)置函數(shù),isset要快一些.請(qǐng)參考：PHP 函數(shù)實(shí)現(xiàn)原理及性能分析
PHP教程3.當(dāng)用isset拜訪一個(gè)不存在索引數(shù)組值時(shí),不會(huì)引起一個(gè)E_NOTICE的php錯(cuò)誤消息；
PHP教程4.array_key_exists 會(huì)調(diào)用get_defined_vars判斷數(shù)組變量是否存在,isset不用；
PHP教程測試代碼：
PHP教程
<?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";
PHP教程希望本文所述對(duì)大家的php程序設(shè)計(jì)有所贊助.
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