Detailed explanation of the use of php array_key_exists() array function

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
$a = array(&#39;a&#39;=>&#39;Dog&#39;,&#39;b&#39;=>&#39;Cat&#39;);
if(array_key_exists(&#39;a&#39;,$a)){
  echo &#39;Key exists!&#39;;
} else{
  echo &#39;Key does not exist!&#39;;
}
?>

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[&#39;aa&#39;]=&#39;dd&#39;;
$test_arr[&#39;bb&#39;]=&#39;&#39;;
$test_arr[&#39;cc&#39;]=NULL;
$test_arr[&#39;dd&#39;]=false;
$test_arr= array(&#39;aa&#39;=>&#39;dd&#39;,&#39;bb&#39;=>&#39;&#39;,&#39;cc&#39;=>null,&#39;dd&#39;=>false);
echo "isset aa is ";var_dump(isset($test_arr[&#39;aa&#39;]));echo "n";
echo "isset bb is ";var_dump(isset($test_arr[&#39;bb&#39;]));echo "n";
echo "isset cc is ";var_dump(isset($test_arr[&#39;cc&#39;]));echo "n";
echo "isset dd is ";var_dump(isset($test_arr[&#39;cc&#39;]));echo "n";
echo "isset none is ";var_dump(isset($test_arr[&#39;none&#39;]));echo "n";
echo "key_exist aa is ";var_dump(array_key_exists(&#39;aa&#39;,$test_arr));echo "n";
echo "key_exist bb is ";var_dump(array_key_exists(&#39;bb&#39;,$test_arr));echo "n";
echo "key_exist cc is ";var_dump(array_key_exists(&#39;cc&#39;,$test_arr));echo "n";
echo "key_exist dd is ";var_dump(array_key_exists(&#39;dd&#39;,$test_arr));echo "n";
echo "key_exist none is ";var_dump(array_key_exists(&#39;none&#39;,$test_arr));echo "n";
$time_start = microtime_float();
for($i=0;$i<100;$i++){
isset($test_arr[&#39;aa&#39;]);
}
$time_end = microtime_float();
$time = $time_end - $time_start;
echo "isset 100 is $timen";
for($i=0;$i<10000;$i++){
isset($test_arr[&#39;aa&#39;]);
}
$time_end = microtime_float();
$time = $time_end - $time_start;
echo "isset 10000 is $timen";
for($i=0;$i<1000000;$i++){
isset($test_arr[&#39;aa&#39;]);
}
$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(&#39;aa&#39;,$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(&#39;aa&#39;,$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(&#39;aa&#39;,$test_arr);
}
$time_end = microtime_float();
$time = $time_end - $time_start;
echo "array_key_exists 1000000 is $timen";

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