章 11. 类型

介绍

PHP 支持八种原始类型。

四种标量类型:

两种复合类型:

最后是两种特殊类型:

为了确保代码的易读性,本手册还介绍了一些伪类型

可能还会读到一些关于“双精度(double)”类型的参考。实际上 double 和 float 是相同的,由于一些历史的原因,这两个名称同时存在。

变量的类型通常不是由程序员设定的,确切地说,是由 PHP 根据该变量使用的上下文在运行时决定的。

注: 如果想查看某个表达式的值和类型,用 var_dump()

注: 如果只是想得到一个易读懂的类型的表达方式用于调试,用 gettype()。要查看某个类型,不要gettype(),而用 is_type 函数。以下是一些范例:

<?php
$bool
= TRUE;   // a boolean
$str  = "foo";  // a string
$int  = 12;     // an integer

echo gettype($bool); // prints out "boolean"
echo gettype($str);  // prints out "string"

// If this is an integer, increment it by four
if (is_int($int)) {
    
$int += 4;
}

// If $bool is a string, print it out
// (does not print out anything)
if (is_string($bool)) {
    echo
"String: $bool";
}
?>

如果要将一个变量强制转换为某类型,可以对其使用强制转换或者 settype() 函数。

注意变量根据其当时的类型在特定场合下会表现出不同的值。更多信息见类型戏法。此外,你还可以参考 PHP 类型比较表看不同类型相互比较的例子。


add a note add a note User Contributed Notes
arjini at gmail dot com
07-Dec-2005 04:32
Note that you can chain type castng:

var_dump((string)(int)false); //string(1) "0"
shahnaz khan
18-Mar-2005 08:40
if we use gettype() before initializinf any variable it give NULL
for eg.

<?php
$foo
;
echo
gettype($foo);
?>

it will show

NULL
Trizor of www.freedom-uplink.org
30-Jun-2004 09:14
The differance of float and double dates back to a FORTRAN standard. In FORTRAN Variables aren't as loosly written as in PHP and you had to define variable types(OH NOES!). FLOAT or REAL*4 (For all you VAX people out there) defined the variable as a standard precision floating point, with 4 bytes of memory allocated to it. DOUBLE PRECISION or REAL*8 (Again for the VAX) was identical to FLOAT or REAL*4, but with an 8 byte allocation of memory instead of a 4 byte allocation.

In fact most modern variable types date back to FORTRAN, except a string was called a CHARACHTER*N and you had to specify the length, or CHARACHTER*(*) for a variable length string. Boolean was LOGICAL, and there weren't yet objects, and there was support for complex numbers(a+bi).

Of course, most people reading this are web programmers and could care less about the mathematical background of programming.

NOTE: Object support was added to FORTRAN in the FORTRAN90 spec, and expanded with the FORTRAN94 spec, but by then C was the powerful force on the block, and most people who still use FORTRAN use the FORTRAN77.
philip at cornado dot com
06-Jun-2001 03:02
To see if something is numeric (a number) then use is_numeric().  All form data is returned as strings so checking a form value as an integer will return false.

http://www.php.net/is_numeric