PHP commonly used array functions

* Functions should mainly understand the following points?

* 1. Function: What can it do?

* 2. Scenario: Where is it used?

* 3. Parameters: required and optional

* 4. Return value: type and quantity

* 1. Key and value operations (6)

* 1. in_array(value, array): Whether val is in array, return Boolean value

* 2. array_key_exists(key, array): Whether key is in array, return Boolean value

* 3. array_values(array): Returns the value part of array in index mode

* 4. array_keys(array[,value]): Returns the key part of array in index mode, and can also return the key of the specified value

* 5. array_search(value, array): Return the key of the specified value in string format

* 6. array_filp(array): Key value swap

* 2. Inside the array Pointer (cruise) operations (8)

* 1. key(array): returns the key of the current element

* 2. current(array): the value of the current element, pos() It is a function with the same name

* 3. next(array): The pointer moves down, pointing to the next element, and returns the current value

* 4. reset(array): The pointer is reset, pointing to the first element element, and return its value

* 5. end(array): The pointer moves to the last element

* 6. prev(array): The pointer moves forward one bit, and returns The value of the current element

* 7. each(array): Returns the index and associated description of the key value of the current element, and automatically moves the pointer down

* 8. list($a ,$b,...): Assign the values ​​in the index array to a set of variables

echo &#39;<pre class="brush:php;toolbar:false">&#39;;
$user = [&#39;id&#39;=>5,&#39;name&#39;=>&#39;peter&#39;,&#39;gender&#39;=>&#39;male&#39;,&#39;age&#39;=>30];
print_r($user); //查看数组
echo &#39;<hr color="red">&#39;;

//1. Commonly used operation functions for keys and values ​​in arrays

// 1. in_array(value, array): Whether val is in the array, return a Boolean value

echo in_array(&#39;Peter Zhu&#39;,$user) ? &#39;存在<br>&#39; : &#39;不存在<br>&#39;;

//2. array_key_exists(key, array): Whether the key is in the array, return a Boolean value

echo array_key_exists(&#39;name&#39;,$user) ? &#39;存在<br>&#39; : &#39;不存在<br>&#39;;

//3.array_values(array): Return the value part of array in index mode

print_r(array_values($user));

//4.array_keys(array[,value]): Return the key part of array in index mode

print_r(array_keys($user));

//4-1.array_keys(array[,value]): Returns the key part of the array in index mode, and can also return the key of the specified value

print_r(array_keys($user,'male'));

//5. array_search(value, array): Return the key of the specified value in string mode

print_r(array_search('peter', $user));

//6. array_filp(array): key value swap

print_r(array_flip($user));

// 2. Array internal pointer (cruise) operation

//count(array)The number of elements in the current array

echo count($user),&#39;<br>&#39;;

//The current pointer points to the first element

//1.key(array): Returns the key of the current element

echo key($user),&#39;<br>&#39;;

//2.current(array): The value of the current element, pos() is the function of the same name

 echo  current($user), &#39;<br>&#39;;

//3.next(array): The pointer moves down, pointing to the next Element

next($user);

//View the key value of the current element

 echo key($user),&#39;<br>&#39;;
 echo  current($user), &#39;<br>&#39;;

//Next(array) can also return in addition to moving the pointer down The value of the current element

var_dump(next($user)); 
 echo key($user),&#39;<br>&#39;;
 echo  current($user), &#39;<br>&#39;;

//Continue to traverse downwards and find that next(array) returns false, indicating that the traversal is over

var_dump(next($user));

//There is no data at the end, there will be no more output

 echo key($user),&#39;<br>&#39;;
 echo  current($user), &#39;<br>&#39;;

//4.reset(array): The pointer is reset, points to the first element, and returns its value

reset ($user);

//In addition to reset, the value of the first element can also be returned

// var_dump(reset($user));

echo key($user),&#39;<br>&#39;;
echo  current($user), '
';

//5. end(array): The pointer moves to the last element

end($user);

// var_dump(end($user)); //Can also return the current The value of the element

echo key($user),&#39;<br>&#39;;
echo  current($user), '
'；

//6. prev(array): The pointer moves forward one bit and returns the value of the current element

prev($user);
echo key($user),&#39;<br>&#39;;
echo  current($user), '
';

//7. each(array): Returns the current The index of the element's key value and the associated description of the array, and the pointer is automatically moved down

* Returns an array of four elements:

* 2 index elements, [0] is the key, [ 1] is the value

* 2 associated elements, [key] is the key, [value] is the value

@print_r(each($user));

/ /Note: Due to execution efficiency issues, this function has been abandoned in php7

//8. list($a,$b,...): Assign the value in the index array to a group Variable

reset($user);  //复位指针

* Operation performed:

* 1.each($user): Get the index part of the current element

* 2.list($key, $value ): The value of [0] is assigned to the variable $key, the value of [1] is assigned to the variable $value

* 3. The array $user pointer automatically moves down

list($key, $value) = each($user);
echo $key,&#39;=>&#39;.$value,&#39;<br>&#39;;

//Repeated call

list($key, $value) = each($user);
echo $key,&#39;=>&#39;.$value,&#39;<br>&#39;;

//Very suitable for loop implementation

echo &#39;<hr color="blue">&#39;;
reset($user);
while(list($key, $value) = each($user)) {
echo $key,&#39;=>&#39;.$value,&#39;<br>&#39;;
}