Summary analysis of PHP data types_PHP tutorial-PHP Tutorial-php.cn

PHP共有8中数据类型：

类型名称	类型表示	取值
bool	布尔型	true,false
integer	整型	-2147483647-2147483648
string	字符串型	字符串长度取决于机器内存
float	浮点型	最大值1.8e308
object	对象	通过new实例化 $obj=new person();
array	数组类型	$arr=array(1,2,3,4,5,6);//一维数组
resourse
null	空值	null

布尔型bool :
对于其他类型我们可以使用（bool）或者（boolean）进行强制转换 eg：（bool）1=true;
以下几种情况在强制转化的时候默认为false：

转换	结果
布尔型的false var_dump((bool) false)	bool(false)
整型0 var_dump((bool) 0);	bool(false)
浮点型0.0 var_dump((bool) 0.0);	bool(false)
字符串‘0' var_dump((bool) '0');	bool(false)
空数组$arr=array(); var_dump((bool) $arr)	bool(false)
不包含任何成员变量的空对象只在PHP4使用,PHP5中为true	bool(false)
NULL或者尚未赋值的变量var_dump((bool) NULL)	bool(false)
从没有任何标记（tags）的XML文档生成的SimpleXML 对象	bool(false)

The conversion result of string '0.0' is bool(true)
Note: -1 and other non-zero values (regardless of positive or negative) are true

Integer type integer:
The range of integer type is -2147483647--2147483647. If it exceeds this value, it will be automatically converted to float type
We can use echo PHP_INT_SZIE to output the word length of integer, which depends on the machine. echo PHP_INT_MAX outputs the maximum value of integer
There is no integer division operation in PHP. If 1/2 is executed, 0.5 of float will be generated. If you want to achieve integer division effect, you can use (int)(1/2)=0 or round(25/ 7)=4
Forcibly converted to integer type (int) or (integer) bool type true is converted to 1, false is converted to 0

Floating point type float:
The maximum value of the value range: 1.8e308. I don’t know what the minimum value is? Experts please tell me
The word length of floating point numbers is also related to the machine. It seems that there is no PHP_FLOAT_SIZE. Ah, experts please tell me how to get the length of floating point numbers

String type string:
4 ways to define strings:
1. Single quotes
2. Double quotes
3. heredoc syntax structure
4. nowdoc syntax structure (after PHP5.3.0)
Single quotes
Single quotes define the original string, and everything inside is processed as a string. If the string contains single quotes, you can use escapes
Double quotes
The string defined by double quotes will To parse some special characters (n, b) and variables
, you can place the variable in double quotes instead of converting the variable into a string (string):
$num=10;
$str = "$num"; //$str is a string type 10
heredoc syntax structure
<<String itself
Identifier
The end mark The identifier must be at the beginning of a line, and the definition format of the identifier must also be in accordance with the rules defined by PHP. It can only contain numbers, letters, and underscores, and cannot start with a number or underscore.
ends with the identifier. Which line does not allow other characters? , you can add a semicolon after the identifier, and there must be no tabs or spaces before and after the semicolon. Otherwise, PHP will not be able to parse the identifier and will continue to search for the identifier. If it is not found before the end of the file, it will generate An error
heredoc is a double quote without double quotes, that is, it can contain double quotes without escaping, and can parse special characters and variables
nowdoc syntax structure
<<< 'Identifier'
The string itself
The start identifier of nowdoc must be enclosed in single quotes, the end identifier and other rules are the same as heredoc
nowdoc is a single quote without single quotes, nowdoc contains The string will be output as it is, and the special characters and variables contained in it will not be parsed

If the double quotes contain several situations in array variables
//We first define the following array