array_key_exists()函數判斷某個數組中是否存在指定的key，如果key存在，則返回true，否則返回flase
array_key_exists(key,array);
key：必需。規定鍵名
array：必需。規定輸入的數組
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<?php$a = array('a'=>'Dog','b'=>'Cat');if(array_key_exists('a',$a)){ echo 'Key exists!';} else{ echo 'Key does not exist!';}?> |
輸出：Key exists!
array_key_exists為什么比in_array快？
array_key_exists 和 in_array 查詢的東西都不一樣吧
array_key_exists 判斷是否有鍵值
array_key_exists(a,arr)->if(isset(arr[a]))就是true
而in_array 需要去遍歷值 遍歷到了才跳出循環
追問：
是不是數組的索引有單獨的存儲單元，而且優化過，array_key_exists的時間復雜度是o(1), 而in_array是o(n) ??
追答：
重復雜度來說是這樣
array_key_exists 是判斷某個鍵有沒有值
in_array 要遍歷一次 獲取是否相同 不知道建的情況下必須遍歷
PHP中isset與array_key_exists的區別
1.對于數組值的判斷不同，對于值為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：
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<?phpfunctionmicrotime_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 $timen";for($i=0;$i<10000;$i++){isset($test_arr['aa']);}$time_end = microtime_float();$time = $time_end - $time_start;echo "isset 10000 is $timen";for($i=0;$i<1000000;$i++){isset($test_arr['aa']);}$time_end = microtime_float();$time = $time_end - $time_start;echo "isset 1000000 is $timen";//++++++++++++++++++++++++++++++$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 $timen";for($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 $timen";for($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 $timen"; |
