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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：

<?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 。