Tác dụng của hàm prev()
The prev() function moves the array's internal pointer to the previous element and returns its value.
The following table summarizes the technical details of this function.
| Return Value: | Returns the value of the previous element in the array, or FALSE if the array is empty. |
|---|---|
| Version: | PHP 4+ |
Tip: Every array has an internal pointer that points to the current element in the array. When a new array is created, the current pointer is initialized reference the first element in the array.
Syntax
The basic syntax of the prev() function is given with:
The following example shows the prev() function in action.
Example
Run this code »<?php
// Sample array
$colors = array("red", "green", "blue", "orange", "yellow", "black");
// Getting the values
echo current($colors); // Prints: red
echo next($colors); // Prints: green
echo prev($colors); // Prints: red
?>Parameters
The prev() function accepts the following parameters.
| Parameter | Description |
|---|---|
| array | Required. Specifies the array to work on. |
More Examples
Here're some more examples showing how prev() function actually works:
The following example demonstrates how to get the previous value from an associative array:
Example
Run this code »<?php
// Sample array
$alphabets = array("a"=>"apple", "b"=>"ball", "c"=>"cat", "d"=>"dog");
// Getting the element's values
echo current($alphabets); // Prints: apple
echo next($alphabets); // Prints: ball
echo prev($alphabets); // Prints: apple
// Getting the previous element's key
echo key($alphabets); // Prints: a
?>The prev() function is commonly used along with the following functions:
current()– Returns the value of the current element in an array.next()– Moves the internal pointer of an array to the next element, and returns its value.end()– Moves the internal pointer of an array to its last element, and returns its value.reset()– Set the internal pointer of an array to its first element, and returns its value.key()– Returns the key of the current element in an array.
Here's an example that demonstrates how these functions basically work:
Example
Run this code »<?php
// Sample array
$colors = array("red", "green", "blue", "orange", "yellow", "black");
// Getting the values
echo current($colors); // Prints: red
echo end($colors); // Prints: black
echo current($colors); // Prints: black
echo prev($colors); // Prints: yellow
echo current($colors); // Prints: yellow
echo next($colors); // Prints: black
echo current($colors); // Prints: black
echo reset($colors); // Prints: red
echo current($colors); // Prints: red
// Getting the current element's key
echo key($colors); // Prints: 0
?>