explode() / implode() Since: PHP 4（2000）

// Splits a string by a delimiter and returns an array.
explode($separator, $string, $limit);

// Joins array elements into a string.
implode($separator, $array);

// Splits a string into an array of chunks of a given length.
str_split($string, $length);

explode() and str_split() return an array. implode() returns the joined string.

<?php
// Splits a comma-separated string into an array.
$csv = "apple,orange,grape";
$fruits = explode(",", $csv);
var_dump($fruits); // Outputs array("apple", "orange", "grape").

// Limits the number of splits.
$data = "Yamada:Taro:30:Tokyo";
$parts = explode(":", $data, 3);
var_dump($parts); // Outputs array("Yamada", "Taro", "30:Tokyo"). The remainder is stored as the last element.

// Joins an array into a string.
$words = ["PHP", " is", " fun"];
echo implode("", $words); // Outputs "PHP is fun".

// Joins with a delimiter.
$tags = ["HTML", "CSS", "JavaScript"];
echo implode(", ", $tags); // Outputs "HTML, CSS, JavaScript".

// Builds an SQL IN clause.
$ids = [1, 5, 12, 23];
$in_clause = implode(",", $ids);
echo "SELECT * FROM users WHERE id IN ($in_clause)"; // Builds the IN clause.

// Splits a string into individual characters with str_split().
$chars = str_split("Hello");
var_dump($chars); // Outputs array("H", "e", "l", "l", "o").

// Splits a string into chunks of a specified length with str_split().
$code = "ABCDEFGHIJ";
$chunks = str_split($code, 3);
var_dump($chunks); // Outputs array("ABC", "DEF", "GHI", "J").

// Parses a file path into its segments.
$path = "/var/www/html/index.php";
$segments = explode("/", trim($path, "/"));
var_dump($segments); // Outputs array("var", "www", "html", "index.php").

explode() and implode() are functions for converting between strings and arrays. They are used extremely often in PHP development for tasks such as processing CSV data, parsing URLs and file paths, and building SQL statements.

Passing a positive integer as the third argument to explode() sets the maximum number of elements; the remaining portion of the string is stored together in the last element. Passing a negative integer excludes that many elements from the end. Note that passing an empty string as the separator causes an error. Use str_split() to split a string character by character.

str_split() splits by character count rather than a delimiter, making it convenient for processing fixed-width data and chunking strings. Use str_replace() to replace substrings and strpos() to search within strings.