Built-in Functions in PHP: A Complete Beginner’s Guide

11/19/2025
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PHP built-in functions with examples.

Built-in Functions in PHP: A Complete Beginner’s Guide

Built-in Functions in PHP: A Complete Beginner’s Guide

PHP comes with hundreds of built-in functions that make development faster, easier, and more efficient. These functions help you perform common tasks like string manipulation, mathematical operations, array processing, date handling, file operations, and much more—without writing extra code.

This guide explains what built-in functions are, how to use them, and includes essential examples for beginners.

What Are Built-in Functions in PHP?

Built-in functions are predefined functions provided by PHP. You can call them directly without having to write them yourself.

Examples include:

  • strlen() for string length

  • count() for counting array elements

  • round() for rounding numbers

  • date() for date/time formatting

These functions save time and improve productivity.

Syntax of a Built-in Function

All built-in functions follow the same basic structure:

functionName(parameter1, parameter2, ...);

Example:

<?php
echo strlen("Hello PHP");  // Output: 9
?>

1. String Functions in PHP

PHP provides many functions to handle and manipulate strings.

1. strlen() – Get string length

<?php
echo strlen("Hello"); // Output: 5
?>

2. strrev() – Reverse a string

<?php
echo strrev("PHP"); // Output: PHP reversed
?>

3. strtolower() / strtoupper()

echo strtolower("HELLO WORLD");
echo strtoupper("hello");

4. strpos() – Find position of a substring

<?php
echo strpos("Hello World", "World"); // Output: 6
?>

2. Array Functions in PHP

1. count() – Count elements in an array

<?php
$colors = ["Red", "Green", "Blue"];
echo count($colors); // Output: 3
?>

2. array_merge() – Merge arrays

<?php
$a = [1, 2];
$b = [3, 4];
print_r(array_merge($a, $b));
?>

3. in_array() – Check if value exists

<?php
if (in_array("Red", $colors)) {
    echo "Found";
}
?>

3. Mathematical Functions in PHP

1. abs() – Absolute value

echo abs(-10); // Output: 10

2. round() – Round a number

echo round(10.67); // Output: 11

3. rand() – Generate random number

echo rand(1, 100);

4. Date & Time Functions in PHP

1. date() – Format date/time

<?php
echo date("Y-m-d H:i:s");
?>

2. time() – Current Unix timestamp

echo time();

3. strtotime() – Convert string to timestamp

echo strtotime("next Monday");

5. File Handling Functions

1. file_get_contents()

Read the contents of a file.

$content = file_get_contents("sample.txt");

2. file_put_contents()

Write to a file.

file_put_contents("demo.txt", "Hello PHP!");

3. fopen(), fwrite(), fclose()

Low-level file operations.

6. Utility Functions

1. isset() – Check if variable exists

if (isset($name)) {
   echo "Variable is set";
}

2. empty() – Check if variable is empty

if (empty($data)) {
    echo "No data";
}

3. var_dump() – Display variable info

var_dump([1, 2, 3]);

Why Use Built-in Functions?

  • Saves time

  • Avoids rewriting logic

  • Increases efficiency

  • Reduces bugs

  • Improves performance

PHP’s built-in functions are optimized and fast, making them preferable over custom solutions.

Common Mistakes Beginners Make

  • Wrong number of parameters
  • Case sensitivity errors (PHP functions are not case-sensitive)
  • Passing wrong data types
  • Forgetting to check for null or empty values

Conclusion

PHP built-in functions make development faster and easier by providing ready-made tools for handling strings, arrays, numbers, files, and more. Mastering these functions will help you write cleaner, more efficient code and speed up your PHP development workflow.

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