PHP Casting Complete Guide | Type Conversion and Casting Techniques at phponline.in

Table of Contents:

PHP Casting: Complete Beginner to Advanced Guide

At phponline.in, we aim to make PHP concepts crystal clear. This guide covers PHP casting (also called type casting or type conversion) from beginner to advanced level. By the end, you’ll understand how to convert variables between different data types effectively, using both explicit casting and implicit type juggling.

You will learn

Introduction to PHP Casting
Why Type Casting is Important
PHP Data Types Recap
Implicit Casting (Type Juggling)
Explicit Casting in PHP
Integer Casting
Float Casting
String Casting
Boolean Casting
Array Casting
Object Casting
Null Casting
Casting and Functions
Casting with Type Declarations in PHP 7 and 8
Real-World Casting Examples
Common Casting Mistakes
PHP Type Comparison vs. Casting
Performance Considerations

1. Introduction to PHP Casting

Casting is the process of changing the data type of a variable in PHP. For example, converting a string like "123" into an integer 123.

PHP is loosely typed, meaning it can automatically change types based on context. However, you can manually control this with casting.

2. Why Type Casting is Important

Ensures data is in the correct format for calculations
Prevents unexpected results from type juggling
Improves code readability and intent

Example:

$value = "10 apples";
$intValue = (int)$value; // 10

3. PHP Data Types Recap

Before diving into casting, here are PHP’s main data types:

Integer
Float
String
Boolean
Array
Object
NULL
Resource

4. Implicit Casting (Type Juggling)

PHP can automatically convert values:

$x = "5" + 3; // PHP converts "5" to integer 5

This flexibility is convenient but can cause unexpected bugs.

5. Explicit Casting in PHP

Explicit casting forces a value into a specific type:

$intVal = (int)$var;
$floatVal = (float)$var;
$stringVal = (string)$var;

Syntax:

$newVar = (type)$oldVar;

6. Integer Casting

$val = "123";
$intVal = (int)$val; // 123

If the string contains non-numeric characters, casting stops at the first invalid character:

$val = "123abc";
$intVal = (int)$val; // 123

7. Float Casting

$val = "10.56";
$floatVal = (float)$val; // 10.56

Casting to float is useful for currency or precise decimal calculations.

8. String Casting

$num = 123;
$str = (string)$num; // "123"

Useful for concatenation and output.

9. Boolean Casting

$val = 0;
$bool = (bool)$val; // false

Rules:

0, 0.0, "", NULL, and empty arrays become false
Everything else becomes true

10. Array Casting

$val = "Hello";
$arr = (array)$val; // array with single element

Converts a variable into an array.

11. Object Casting

$arr = ["name" => "John"];
$obj = (object)$arr; // stdClass object

12. Null Casting

You can cast any value to NULL:

$val = 100;
$nullVal = (unset)$val; // NULL

13. Casting and Functions

You can cast function results:

$sum = (float)(5 / 2); // 2.5

14. Casting with Type Declarations in PHP 7 and 8

PHP allows type declarations for function parameters and return values:

function addNumbers(int $a, int $b): float {
    return $a + $b;
}

If wrong type is passed, PHP may attempt to cast it (in weak mode) or throw a TypeError (in strict mode).

15. Real-World Casting Examples

Form data processing
API response handling
Database query results conversion
JSON decoding to objects or arrays

16. Common Casting Mistakes

Assuming is_numeric() means value is safe to cast
Forgetting about locale settings in float conversion
Overusing implicit casting without validation

17. PHP Type Comparison vs. Casting

Casting changes the type of a value, whereas type comparison checks if two values are the same type using ===.

18. Performance Considerations

Casting is generally fast, but unnecessary casting can slow down loops or large data processing.

Frequently Asked Questions

What is the difference between implicit and explicit casting in PHP?

Implicit casting is automatic by PHP, explicit casting is done manually by the programmer.

How do I cast a string to an integer in PHP?

Use (int)$string or intval($string).

Can I cast arrays to objects in PHP?

Yes, using (object)$array.

What happens if I cast NULL to another type?

It becomes the empty value for that type.

Does casting affect the original variable?

No, casting returns a new value without changing the original variable.

PHP Casting