array array_slice ( array $array , int $offset [, int $length = NULL [, bool $preserve_keys = false ]] )

<?php
$input = array("a", "b", "c", "d", "e");

$output = array_slice($input, 2);   // returns "c", "d", and "e"
$output = array_slice($input, -2, 1); // returns "d"
$output = array_slice($input, 0, 3);  // returns "a", "b", and "c"

print_r(array_slice($input, 2, -1)); // array(0 => 'c', 1 => 'd');
print_r(array_slice($input, 2, -1, true)); // array(2 => 'c', 1 => 'd');

array array_splice ( array &$input , int $offset [, int $length = 0 [, mixed $replacement = array() ]] )

<?php
$input = array("red", "green", "blue", "yellow");
array_splice($input, 2);
// $input变为 array("red", "green")

$input = array("red", "green", "blue", "yellow");
array_splice($input, 1, -1);
// $input变为 array("red", "yellow")

$input = array("red", "green", "blue", "yellow");
array_splice($input, 1, count($input), "orange");
// $input变为 array("red", "orange")

$input = array("red", "green", "blue", "yellow");
array_splice($input, -1, 1, array("black", "maroon"));
// $input为 array("red", "green",
//     "blue", "black", "maroon")

$input = array("red", "green", "blue", "yellow");
array_splice($input, 3, 0, "purple");
// $input为 array("red", "green",
//     "blue", "purple", "yellow");

 /* Don't create the array of removed elements if it's not going
   * to be used; e.g. only removing and/or replacing elements */
  if (return_value_used) { // 如果有用到函数返回值则创建返回数组，否则不创建返回数组
    int size = length;

    /* Clamp the offset.. */
    if (offset > num_in) {
      offset = num_in;
    } else if (offset < 0 && (offset = (num_in + offset)) < 0) {
      offset = 0;
    }

    /* ..and the length */
    if (length < 0) {
      size = num_in - offset + length;
    } else if (((unsigned long) offset + (unsigned long) length) > (unsigned) num_in)     {
      size = num_in - offset;
    }

    /* Initialize return value */
    array_init_size(return_value, size > 0 ? size : 0);
    rem_hash = &Z_ARRVAL_P(return_value);
  }