我认为最简单的方法是使用带有foreach循环的函数:

//This functions deletes the elements of an array $original that are equivalent to the value $del_val
//The function works by reference, which means that the actual array used as parameter will be modified.

function delete_value(&$original, $del_val)
{
    //make a copy of the original, to avoid problems of modifying an array that is being currently iterated through
    $copy = $original;
    foreach ($original as $key => $value)
    {
        //for each value evaluate if it is equivalent to the one to be deleted, and if it is capture its key name.
        if($del_val === $value) $del_key[] = $key;
    };
    //If there was a value found, delete all its instances
    if($del_key !== null)
    {
        foreach ($del_key as $dk_i)
        {
            unset($original[$dk_i]);
        };
        //optional reordering of the keys. WARNING: only use it with arrays with numeric indexes!
        /*
        $copy = $original;
        $original = array();
        foreach ($copy as $value) {
            $original[] = $value;
        };
        */
        //the value was found and deleted
        return true;
    };
    //The value was not found, nothing was deleted
    return false;
};

$original = array(0,1,2,3,4,5,6,7,4);
$del_val = 4;
var_dump($original);
delete_value($original, $del_val);
var_dump($original);

输出将是:

array(9) {
  [0]=>
  int(0)
  [1]=>
  int(1)
  [2]=>
  int(2)
  [3]=>
  int(3)
  [4]=>
  int(4)
  [5]=>
  int(5)
  [6]=>
  int(6)
  [7]=>
  int(7)
  [8]=>
  int(4)
}
array(7) {
  [0]=>
  int(0)
  [1]=>
  int(1)
  [2]=>
  int(2)
  [3]=>
  int(3)
  [5]=>
  int(5)
  [6]=>
  int(6)
  [7]=>
  int(7)
}

要删除多个值，试试这个:

while (($key = array_search($del_val, $messages)) !== false) 
{
    unset($messages[$key]);
}

从数组中删除一个元素基本上就是设置一个元素的差异。

array_diff( [312, 401, 15, 401, 3], [401] ) // removing 401 returns [312, 15, 3]

它很好地泛化了，你可以同时删除任意多的元素，如果你想的话。

免责声明:请注意，我的解决方案产生了一个新的数组副本，同时保持旧的完整，与变异的接受答案形成对比。选一个你需要的。

在PHP 7.4中使用箭头函数:

$messages = array_filter($messages, fn ($m) => $m != $del_val);

为了保持它是一个非关联数组，用array_values()来包装它:

$messages = array_values(array_filter($messages, fn ($m) => $m != $del_val));

function array_remove_by_value($array, $value)
{
    return array_values(array_diff($array, array($value)));
}

$array = array(312, 401, 1599, 3);

$newarray = array_remove_by_value($array, 401);

print_r($newarray);

输出

Array ([0] => 312 [1] => 1599 [2] => 3)

如果你不知道它的键，那就意味着它无关紧要。

你可以将值作为键，这意味着它会立即找到值。比在所有元素中反复搜索要好。

$messages=array();   
$messages[312] = 312;    
$messages[401] = 401;   
$messages[1599] = 1599;   
$messages[3] = 3;    

unset($messages[3]); // no search needed