array_key_exists()函数判断某个数组中是否存在指定的key,如果key存在,则返回true,否则返回flase
array_key_exists(key,array);
key:必需。规定键名
array:必需。规定输入的数组
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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!' ; } ?> |
输出:Key exists!
array_key_exists为什么比in_array快?
array_key_exists 和 in_array 查询的东西都不一样吧
array_key_exists 判断是否有键值
array_key_exists(a,arr)->if(isset(arr[a]))就是true
而in_array 需要去遍历值 遍历到了才跳出循环
追问:
是不是数组的索引有单独的存储单元,而且优化过,array_key_exists的时间复杂度是o(1), 而in_array是o(n) ??
追答:
重复杂度来说是这样
array_key_exists 是判断某个键有没有值
in_array 要遍历一次 获取是否相同 不知道建的情况下必须遍历
PHP中isset与array_key_exists的区别
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:
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<?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 $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" ; |