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PHP - Type Casting

The term "Type Casting" refers to the conversion of one type of data to another. Since PHP is a weakly typed language, the parser coerces certain data types into others while performing certain operations. For example, a string containing digits is converted to an integer if it is one of the operands involved in an addition operation.

Implicit Type Casting​

Here is an example of coercive or implicit type casting:

<?php
$a = 10;
$b = '20';
$c = $a + $b;
echo "c = " . $c;
?>

In this case, $b is a string variable cast into an integer to enable addition. It will produce the following output:

c = 30

Let's take another example where an integer variable $a is converted to a string for concatenation with a string variable:

<?php
$a = 10;
$b = '20';
$c = $a . $b;
echo "c = " . $c;
?>

It will produce the following output:

c = 1020

In addition to coercive type conversion, PHP provides ways to explicitly cast one type of data to another using type casting operators or functions.

Type Casting Operators​

To convert an expression of one type to another, you can use type casting operators. Here are some examples:

  • (int) or (integer) casts to an integer.
  • (bool) or (boolean) casts to a boolean.
  • (float) or (double) or (real) casts to a float.
  • (string) casts to a string.
  • (array) casts to an array.
  • (object) casts to an object.

Casting to Integer​

You can convert a float value to an integer using (int):

<?php
$a = 9.99;
$b = (int)$a;
var_dump($b);
?>

It will produce the following output:

int(9)

The float value is not rounded to the nearest integer; instead, it returns the integer part.

String to Integer Conversion​

The (int) operator also converts a string to an integer. If the string contains only digits, the conversion is straightforward:

<?php
$a = "99";
$b = (int)$a;
var_dump($b);
?>

Output:

int(99)

Even if the string contains a floating-point number, (int) returns just the integer part. However, if the string is alphanumeric, the conversion behaves differently:

  • If the string starts with digits followed by non-numeric characters, only the initial digits are considered.
  • If the string starts with non-numeric characters and digits are in the middle, the operator returns "0".
<?php
$a = "10 Rs.";
$b = (int)$a;
var_dump($b);

$a = "$100";
$b = (int)$a;
var_dump($b);
?>

Output:

int(10)
int(0)

Casting to Float Type​

You can use (float) or (double) to explicitly convert to a float:

<?php
$a = 100;
$b = (double)$a;
var_dump($b);
?>

Output:

float(100)

A string containing a valid numeric representation may also be cast to float using these operators.

Handling Scientific Notation​

Strings with scientific notation can also be converted to float:

<?php
$a = "1.23E01";
$b = (double)$a;
var_dump($b);

$a = "5.5E-5";
$b = (float)$a;
var_dump($b);
?>

Output:

float(12.3)
float(5.5E-5)

Non-numeric characters after the floating-point numbers are ignored. If the string starts with non-numeric characters, the conversion returns "0".

Casting to String Type​

You can cast expressions evaluating to floating-point or integer to string using (string):

<?php
$a = 100;
$b = (string)$a;
var_dump($b);

$x = 55.50;
$y = (string)$x;
var_dump($y);
?>

Output:

string(3) "100"
string(4) "55.5"

Casting to Bool Type​

Non-zero numbers (integer or float) cast to true with (bool). A value of "0" returns false. Strings are always cast to true.

<?php
$a = 100;
$b = (bool)$a;

$x = 0;
$y = (bool)$x;

$m = "Hello";
$n = (bool)$m;

var_dump($b);
var_dump($y);
var_dump($n);
?>

Output:

bool(true)
bool(false)
bool(true)

Type Casting Functions​

PHP includes built-in functions for type casting:

  • intval()
  • floatval()
  • strval()

The intval() Function​

This function gets the integer value of a variable.

<?php
echo intval(42) . PHP_EOL;
echo intval(4.2) . PHP_EOL;
echo intval('42') . PHP_EOL;

echo intval(042) . PHP_EOL;        // Octal number
echo intval('042', 0) . PHP_EOL;   // Octal number
echo intval('42', 8) . PHP_EOL;    // Octal

echo intval(0x1A) . PHP_EOL;       // Hexadecimal
echo intval('0x1A', 16) . PHP_EOL; // Hexadecimal
echo intval('0x1A', 0) . PHP_EOL;  // Hexadecimal

echo intval(false) . PHP_EOL;
echo intval(true) . PHP_EOL;
?>

Output:

42
4
42
34
34
34
26
26
26
0
1

The floatval() Function​

This function gets the float value of an expression.

<?php
echo floatval(42) . PHP_EOL;
echo floatval(4.2) . PHP_EOL;
echo floatval('42') . PHP_EOL;

echo floatval('99.90 Rs') . PHP_EOL;
echo floatval('$100.50') . PHP_EOL;
echo floatval('ABC123!@#') . PHP_EOL;

echo (true) . PHP_EOL;
echo (false) . PHP_EOL;
?>

Output:

42
4.2
42
99.9
0
0
1

The doubleval() function is an alias of floatval() and returns similar results.

The strval() Function​

This function gets the string value of a variable.

<?php
echo strval(42) . PHP_EOL;
echo strval(4.2) . PHP_EOL;
echo strval(4.2E5) . PHP_EOL;

echo strval(NULL) . PHP_EOL;

echo (true) . PHP_EOL;
echo (false) . PHP_EOL;
?>

Output:

42
4.2
420000

1

If the value being converted to a string is an object that implements the __toString() method, strval() uses that method.

<?php
class myclass {
   public function __toString() {
      return __CLASS__;
   }
}
echo strval(new myclass);
?>

Output:

myclass