PHP中isset與array_key_exists的區別實例分析

本文實例講述了PHP中isset與array_key_exists的區別。分享給大家供大家參考。具體分析如下：

1.對於數組值的判斷不同，對於值為null或''或false,isset返回false，array_key_exists返回true；

2. 執行效率不同，isset是內建運算符，array_key_exists是php內置函數，isset要快一些。請參考：PHP 函數實現原理及性能分析

3.當用isset訪問一個不存在索引數組值時，不會引起一個E_NOTICE的php錯誤消息；

4.array_key_exists 會調用get_defined_vars判斷數組變量是否存在，isset不用；

測試代碼：

<?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";

希望本文所述對大家的php程序設計有所幫助。