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This article summarizes the knowledge about php arrayfunctionarray_key_exists() and the performance comparison with in_array, and the difference analysis with isset, which is very For details, friends in need can refer to it.
array_key_exists() function determines whether the specified key exists in an array. If the key exists, it returns true, otherwise it returns false
array_key_exists(key,array);
key: required. Specify key name
array: required. Specify the input array
<?php $a = array('a'=>'Dog','b'=>'Cat'); if(array_key_exists('a',$a)){ echo 'Key exists!'; } else{ echo 'Key does not exist!'; } ?>
Output: Key exists!
Why is array_key_exists faster than in_array?
array_key_exists and in_array query things are different
array_key_exists determine whether there is a key value
array_key_exists(a,arr)->if(isset(arr[a])) It is true
And in_array needs to traverse the value before jumping out of the loop
Question:
Does the index of the array have a separate storage unit and is optimized? The time complexity of array_key_exists is o(1), and in_array is o(n) ??
Follow-up answer:
In terms of complexity, this is the case
array_key_exists is to determine whether a certain key has No value
in_array To traverse once to obtain whether they are the same, you must traverse if you don’t know the construction
The difference between isset and array_key_exists in PHP
1. The judgment of array values is different. If the value is null or '' or false, isset returns false, and array_key_exists returns true;
2. The execution efficiency is different, isset is a built-inoperator, array_key_exists is phpbuilt-in function, isset is faster. Please refer to: PHP function implementation principle and performance analysis
3. When using isset to access a non-existent index array value, it will not cause a PHP error message of E_NOTICE;
4.array_key_exists will Call get_defined_vars to determine whether the array variable exists, isset is not used;
Test code:
<?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";
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