Discrimination of php type conversion

PHP does not require (or support) explicit type definitions in variable definitions; the variable type is determined based on the context in which the variable is used. That is, if you assign a string value to the variable $var, $var becomes a string. If you assign an integer value to $var, it becomes an integer.

An example of PHP’s automatic type conversion is the addition operator “+”. If any operand is a floating point number, all operands are treated as floating point numbers, and the result is also a floating point number. Otherwise the operands are interpreted as integers and the result is also an integer. Note that this does not change the types of the operands themselves; only how the operands are evaluated and the type of the expression itself is changed.

<?php
$foo = "0";  // $foo 是字符串 (ASCII 48)
$foo += 2;   // $foo 现在是一个整数 (2)
$foo = $foo + 1.3;  // $foo 现在是一个浮点数 (3.3)
$foo = 5 + "10 Little Piggies"; // $foo 是整数 (15)
$foo = 5 + "10 Small Pigs";     // $foo 是整数 (15)
?>

If you want to test any of the examples in this section, you can use the var_dump() function.

Note:

The behavior of automatic conversion to an array is currently undefined.

In addition, since PHP supports accessing string subscripts using the same syntax as array subscripts, the following example is valid in all PHP versions:

$a = 'car'; // $a is a string
$a[0] = 'b'; // $a is still a string
echo $a; // bar
?>

Type casting

Type casting in PHP and C Much like: precede the variable to be converted with the target type enclosed in parentheses.

<?php
$foo = 10;   // $foo is an integer
$bar = (boolean) $foo;   // $bar is a boolean
?>

The allowed casts are:

(int), (integer) - converted to integer

(bool), (boolean) - converted to boolean type boolean

(float), (double), (real ) - Convert to float float

(string) - Convert to string string

(array) - Convert to array array

(object) - Convert to object object

(unset) - Convert to NULL (PHP 5)

(binary) conversion and b prefix conversion support are newly added for PHP 5.2.1.

Note that spaces and tabs are allowed within brackets, so the following two examples have the same function:

$foo = (int) $bar;
$foo = (int) $bar;
? >

Convert string literals and variables to binary strings:

$binary = (binary)$string;
$binary = b"binary string";
?>

Note:

Instead of converting a variable to a string, you can place it in double quotes:

<?php
$foo = 10;            // $foo 是一个整数
$str = "$foo";        // $str 是一个字符串
$fst = (string) $foo; // $fst 也是一个字符串// 输出 "they are the same"
if ($fst === $str) {
echo "they are the same";
}
?>

Sometimes it may not be obvious what exactly happens when casting between types. See below for more information:

Convert to Boolean

Convert to Integer

Convert to Float

Convert to String

Convert to Array

Convert to Object

Convert to Resource

Convert to NULL