PHP array_key_exists () array functions using an explanation

This article gives you a summary of the PHP array function array_key_exists () knowledge and performance comparison with In_array, and the isset of the difference analysis, very detailed, the need for small partners can refer to.

The array_key_exists () function determines whether the specified key exists in an array, returns true if key exists, or returns flase

Array_key_exists (Key,array);

Key: Required. Specified key Name
Array: Required. Specify an array of inputs

<?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 are not the same thing.
Array_key_exists determine if there is a key value
Array_key_exists (A,arr)->if (Isset (Arr[a])) is true

And the In_array needs to traverse the value to traverse it before jumping out of the loop

Ask:
is the index of the array has a separate storage unit, and optimized, array_key_exists time complexity is O (1), and In_array is O (n)??

Chase Answer:
In terms of complexity.

Array_key_exists is to determine if a key has a value

In_array to traverse once to get whether the same does not know the built case must traverse

The difference between isset and array_key_exists in PHP

1. For the value of the array is different, for a value of NULL or ' or false,isset return false,array_key_exists true;

2. Execution efficiency is different, isset is built-in operator, Array_key_exists is PHP built-in function, isset to be 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 e_notice PHP error message;

4.array_key_exists will call Get_defined_vars to determine if the array variable exists, isset not;

Test code:

<?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 "; 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" $timen "; for ($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 $timen"; for ($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";