PHP Built-in Functions (Step-by-Step Guide with Examples)

PHP comes with hundreds of built-in functions that simplify coding tasks. These functions handle strings, arrays, math, dates, file operations, and more.

1. What Are Built-in Functions in PHP?

Built-in functions are predefined PHP functions that perform specific tasks. You can call them directly without defining them.

Example: Using `strlen()` to Get String Length

<?php
$text = "Hello, PHP!";
echo strlen($text); // Output: 11
?>

➡ The strlen() function counts characters in a string.

2. PHP String Functions

PHP provides functions to manipulate strings.

Common String Functions

Function	Description	Example
`strlen()`	Returns the length of a string	`strlen("Hello") → 5`
`strtoupper()`	Converts a string to uppercase	`strtoupper("php") → PHP`
`strtolower()`	Converts a string to lowercase	`strtolower("PHP") → php`
`strpos()`	Finds the position of the first occurrence of a substring	`strpos("Hello", "e") → 1`
`strrpos()`	Finds the position of the last occurrence of a substring	`strrpos("Hello Hello", "e") → 7`
`str_replace()`	Replaces occurrences of a substring in a string	`str_replace("World", "PHP", "Hello World") → "Hello PHP"`
`substr()`	Extracts a part of a string	`substr("Hello", 1, 3) → "ell"`
`strrev()`	Reverses a string	`strrev("Hello") → "olleH"`
`trim()`	Removes whitespace from both sides of a string	`trim(" Hello ") → "Hello"`
`ltrim()`	Removes whitespace from the left side of a string	`ltrim(" Hello") → "Hello"`
`rtrim()`	Removes whitespace from the right side of a string	`rtrim("Hello ") → "Hello"`
`ucfirst()`	Capitalizes the first letter of a string	`ucfirst("hello") → "Hello"`
`lcfirst()`	Converts the first letter of a string to lowercase	`lcfirst("Hello") → "hello"`
`ucwords()`	Capitalizes the first letter of each word	`ucwords("hello world") → "Hello World"`
`str_repeat()`	Repeats a string a specified number of times	`str_repeat("Hi ", 3) → "Hi Hi Hi "`
`str_shuffle()`	Randomly shuffles the characters in a string	`str_shuffle("hello") → "lohel"` (Random output)
`wordwrap()`	Wraps a string to a given number of characters	`wordwrap("This is a long sentence", 10, "\n")`
`htmlspecialchars()`	Converts special characters to HTML entities	`htmlspecialchars("<b>bold</b>") → "<b>bold</b>"`
`html_entity_decode()`	Converts HTML entities back to characters	`html_entity_decode("<b>bold</b>") → "<b>bold</b>"`
`addslashes()`	Adds backslashes before special characters	`addslashes("I'm PHP") → "I\'m PHP"`
`stripslashes()`	Removes backslashes added by `addslashes()`	`stripslashes("I\'m PHP") → "I'm PHP"`
`number_format()`	Formats a number with grouped thousands	`number_format(10000.456, 2) → "10,000.46"`

String Functions (addcslashes(), chr(), chop())

Function	Description	Example
`addcslashes()`	Escapes characters in a string with a backslash, based on a list of characters	`addcslashes("Hello", "e") → "H\e\llo"`
`chr()`	Returns a one-character string from a given ASCII value	`chr(65) → "A"`
`chop()`	Alias for `rtrim()` — removes whitespace or other characters from the right side of a string	`chop("Hello ") → "Hello"`

Example: Replacing Text in a String

<?php
$text = "I love JavaScript!";
$newText = str_replace("JavaScript", "PHP", $text);
echo $newText; // Output: I love PHP!
?>

3. PHP Array Functions

PHP provides many built-in functions to manipulate arrays. Here’s a list of commonly used array functions:

Function	Description	Example
`count()`	Returns the number of elements in an array	`count([1, 2, 3]) → 3`
`sizeof()`	Alias of `count()`	`sizeof([1, 2, 3]) → 3`
`array_push()`	Adds one or more elements to the end of an array	`$arr = [1, 2]; array_push($arr, 3, 4);` → `[1, 2, 3, 4]`
`array_pop()`	Removes and returns the last element of an array	`$arr = [1, 2, 3]; array_pop($arr);` → `3`
`array_unshift()`	Adds elements to the beginning of an array	`$arr = [2, 3]; array_unshift($arr, 1);` → `[1, 2, 3]`
`array_shift()`	Removes and returns the first element of an array	`$arr = [1, 2, 3]; array_shift($arr);` → `1`
`array_merge()`	Merges two or more arrays	`array_merge([1, 2], [3, 4]) → [1, 2, 3, 4]`
`array_combine()`	Creates an array using one array as keys and another as values	`array_combine(["a", "b"], [1, 2]) → ["a" => 1, "b" => 2]`
`array_slice()`	Extracts a portion of an array	`array_slice([1, 2, 3, 4], 1, 2)` → `[2, 3]`
`array_splice()`	Removes elements and replaces them with new ones	`$arr = [1, 2, 3, 4]; array_splice($arr, 1, 2, ["X"]);` → `[1, "X", 4]`
`array_keys()`	Returns an array of all keys from an array	`array_keys(["a" => 1, "b" => 2]) → ["a", "b"]`
`array_values()`	Returns all values from an array	`array_values(["a" => 1, "b" => 2]) → [1, 2]`
`array_flip()`	Swaps keys with values in an array	`array_flip(["a" => 1, "b" => 2]) → [1 => "a", 2 => "b"]`
`array_reverse()`	Reverses the order of array elements	`array_reverse([1, 2, 3]) → [3, 2, 1]`
`array_unique()`	Removes duplicate values from an array	`array_unique([1, 2, 2, 3]) → [1, 2, 3]`
`in_array()`	Checks if a value exists in an array	`in_array(2, [1, 2, 3]) → true`
`array_search()`	Searches for a value and returns its key	`array_search(2, [1, 2, 3]) → 1`
`array_diff()`	Returns the difference between arrays (values not in the second array)	`array_diff([1, 2, 3], [2, 3]) → [1]`
`array_intersect()`	Returns common values between arrays	`array_intersect([1, 2, 3], [2, 3, 4]) → [2, 3]`
`array_map()`	Applies a function to each element of an array	`array_map('strtoupper', ['a', 'b', 'c']) → ['A', 'B', 'C']`
`array_filter()`	Filters an array using a callback function	`array_filter([1, 2, 3, 4], fn($x) => $x % 2 == 0)` → `[2, 4]`
`array_reduce()`	Reduces an array to a single value using a function	`array_reduce([1, 2, 3], fn($carry, $item) => $carry + $item, 0)` → `6`
`sort()`	Sorts an array in ascending order	`$arr = [3, 1, 2]; sort($arr);` → `[1, 2, 3]`
`rsort()`	Sorts an array in descending order	`$arr = [3, 1, 2]; rsort($arr);` → `[3, 2, 1]`
`asort()`	Sorts an associative array by values	`$arr = ["b" => 2, "a" => 1]; asort($arr);` → `["a" => 1, "b" => 2]`
`ksort()`	Sorts an associative array by keys	`$arr = ["b" => 2, "a" => 1]; ksort($arr);` → `["a" => 1, "b" => 2]`
`shuffle()`	Randomizes the order of elements in an array	`shuffle($arr);` → (Random output)

Example: Merging Arrays

<?php
$frontend = ["HTML", "CSS"];
$backend = ["PHP", "MySQL"];
$fullStack = array_merge($frontend, $backend);
print_r($fullStack);
?>

Output:

4. PHP Math Functions

PHP has built-in functions for mathematical calculations.

Common Math Functions

Function	Description	Example
`abs()`	Absolute value	`abs(-10)` → `10`
`round()`	Rounds a number	`round(4.7)` → `5`
`ceil()`	Rounds up	`ceil(4.3)` → `5`
`floor()`	Rounds down	`floor(4.7)` → `4`
`sqrt()`	Square root	`sqrt(16)` → `4`
`rand()`	Random number	`rand(1,100)`

Example: Generating a Random Number

<?php
echo "Random number: " . rand(1, 100);
?>

5. PHP Date and Time Functions

PHP has built-in functions to handle date and time operations.

Common Date Functions

Function	Description	Example
`date()`	Formats a date/time string	`date("Y-m-d")` → `"2025-02-12"`
`time()`	Returns current timestamp	`time()`
`strtotime()`	Converts string to timestamp	`strtotime("next Monday")`

Example: Displaying the Current Date

<?php
echo "Today is: " . date("Y-m-d");
?>

6. PHP File Handling Functions

PHP provides functions to read, write, and modify files.

Common File Functions

Function	Description	Example
`fopen()`	Opens a file	`fopen("file.txt", "r")`
`fwrite()`	Writes to a file	`fwrite($file, "Hello!")`
`fread()`	Reads file content	`fread($file, filesize("file.txt"))`
`fclose()`	Closes an open file	`fclose($file)`

Example: Writing to a File

<?php
$file = fopen("example.txt", "w");
fwrite($file, "Hello, PHP!");
fclose($file);
?>

7. PHP Miscellaneous Functions

PHP also includes functions for error handling, debugging, and more.

Common Miscellaneous Functions

Function	Description	Example
`var_dump()`	Prints variable details	`var_dump($array)`
`isset()`	Checks if variable is set	`isset($var)`
`empty()`	Checks if variable is empty	`empty($var)`
`die()`	Stops script execution	`die("Error!")`
`exit()`	Same as `die()`	`exit("Stopping!")`

Example: Debugging with `var_dump()`

<?php
$data = ["PHP", "MySQL", "Laravel"];
var_dump($data);
?>

Output:

➡ var_dump() provides detailed output.

PHP Output Functions

PHP provides several functions for outputting data to the browser. These functions are used to display content like strings, variables, or structured data.

Function	Description	Example
`echo()`	Outputs one or more strings without returning a value	`echo "Hello";`
`print()`	Outputs a string and returns 1, so it can be used in expressions	`print "Hello";`
`printf()`	Outputs a formatted string	`printf("My name is %s", "John");` → `My name is John`
`sprintf()`	Returns a formatted string (similar to `printf` but doesn’t output it)	`$str = sprintf("My name is %s", "John"); echo $str;` → `My name is John`
`print_r()`	Prints human-readable information about a variable (useful for arrays and objects)	`print_r([1, 2, 3]);` → `[1, 2, 3]`
`var_dump()`	Dumps detailed information about a variable, including its type and value	`var_dump([1, 2, 3]);` → `array(3) { [0]=> int(1) [1]=> int(2) [2]=> int(3) }`
`var_export()`	Outputs or returns a valid PHP code representation of a variable	`var_export([1, 2, 3]);` → `array ( 0 => 1, 1 => 2, 2 => 3, )`
`ob_start()`	Starts output buffering (to send output to a buffer rather than to the browser)	`ob_start(); echo "Hello"; ob_end_flush();` → `Hello`
`ob_get_contents()`	Gets the current buffer contents (used with output buffering)	`ob_start(); echo "Hello"; $output = ob_get_contents(); ob_end_clean();` → `$output = "Hello"`

Function	Description	Example
`bin2hex()`	Converts a binary string to its hexadecimal representation	`bin2hex("Hello") → "48656c6c6f"`
`chunk_split()`	Splits a string into smaller chunks of a specified length	`chunk_split("abcdef", 2) → "ab\ncd\nef\n"`
`convert_cyr_string()`	Converts a string from one Cyrillic character set to another	`convert_cyr_string("Привет", "w", "k") → "Aopmf"`
`convert_uuencode()`	Encodes a string using uuencode encoding (used for encoding binary data for transmission)	`convert_uuencode("Hello") → "begin 644 /tmp/hello\n#0V%T\nend"`
`convert_uudecode()`	Decodes a string that was uuencoded using `convert_uuencode()`	`convert_uudecode("begin 644 /tmp/hello\n#0V%T\nend") → "Hello"`
`count_chars()`	Returns information about characters used in a string	`count_chars("hello", 3) → Array ( [104] => 1 [101] => 1 [108] => 2 [111] => 1 )`
`explode()`	Splits a string into an array based on a delimiter	`explode(",", "apple,banana,orange") → ["apple", "banana", "orange"]`
`fprintf()`	Writes a formatted string to a file pointer (can be used to format data)	`fprintf($file, "Hello %s", "world") → "Hello world"`
`get_html_translation_table()`	Returns an associative array with HTML entities for characters or their reverse	`get_html_translation_table(HTML_ENTITIES) → Array ( ["<"] => "<" ["&"] => "&" )`
`hebrevc()`	Converts a string to Hebrew, and reverses the order of characters	`hebrevc("שלום") → "םולש"`
`hex2bin()`	Converts a hexadecimal string to its binary representation	`hex2bin("48656c6c6f") → "Hello"`

PHP Built-in Functions (Step-by-Step Guide with Examples)

1. What Are Built-in Functions in PHP?

Example: Using strlen() to Get String Length

2. PHP String Functions

Common String Functions

String Functions (addcslashes(), chr(), chop())

3. PHP Array Functions

Output:

4. PHP Math Functions

Common Math Functions

Example: Generating a Random Number

5. PHP Date and Time Functions

Common Date Functions

Example: Displaying the Current Date

6. PHP File Handling Functions

Common File Functions

Example: Writing to a File

7. PHP Miscellaneous Functions

Common Miscellaneous Functions

Example: Debugging with var_dump()

Output:

PHP Output Functions

Example: Using `strlen()` to Get String Length

Example: Debugging with `var_dump()`