Discrimination of php data 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. In other words, if you assign a string value to the variable $var, $var becomes a string. If you assign an integer to $var, it becomes an integer.

An example of PHP's automatic type conversion is the addition operator"+". If any operand is float , then all operands are treated as float , and the result is also float . Otherwise the operands are interpreted as integer 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 the above two examples seem odd, see Converting Strings to Numbers.

If you want to force a variable to be evaluated as a certain type, see the TypeForcing Conversion section. If you want to change the type of a variable, see settype().

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:

<?php
$a     =  &#39;car&#39; ;  // $a is a string
$a [ 0 ] =  &#39;b&#39; ;    // $a is still a string
echo  $a ;        // bar
?>

Type cast

Type casting in PHP is very similar to that in C: the variable to be converted is preceded by 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) - Convert to Boolean type boolean

• (float), (double), (real) - Convert to floating point type float

• (string) - Convert to string string

• (array) - Convert to array array

• (object) - Convert to object object

• (unset) - Convert to NULL (PHP 5)

(binary) Convert and b Prefix conversion support is new for PHP 5.2.1.

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

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

Convert string literals and variables to binary strings:

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

Note:

Instead of converting the variable to a string, you can place the variable 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" ;
}
?>

The above is the detailed content of Discrimination of php data type conversion. For more information, please follow other related articles on the PHP Chinese website!