var_dump(0) //int(0)
var_dump('0') //string(1) "0"
var_dump('ssddsd') //string(7) "sasadad"
var_dump(0=='sdfsdf') // bool(true)
var_dump('0'=='sdfsf') //bool(false)
在上面这些比较中为什么var_dump(0=='sdfsdf') // bool(true)而var_dump('0'=='sdfsf') //bool(false)
我认为的是0是整形,和字符型'sdfsf'比较应该是false。。。。
为什么实际结果却是相反的,我哪里理解错了么???
回复内容:
var_dump(0) //int(0)
var_dump('0') //string(1) "0"
var_dump('ssddsd') //string(7) "sasadad"
var_dump(0=='sdfsdf') // bool(true)
var_dump('0'=='sdfsf') //bool(false)
在上面这些比较中为什么var_dump(0=='sdfsdf') // bool(true)而var_dump('0'=='sdfsf') //bool(false)
我认为的是0是整形,和字符型'sdfsf'比较应该是false。。。。
为什么实际结果却是相反的,我哪里理解错了么???
<code>var_dump(0=='sdfsdf')</code>
当处理这句时,不同类型比较'sdfsdf'会被强制转换成int型,也就是int 0,所以结果是true
<code>var_dump('0'=='sdfsf') </code>
当处理这句时,相同类型比较直接比较内容,内容不一样,所以结果是false
你可以试试var_dump((int)("sdfsf"));结果是int 0
https://segmentfault.com/q/1010000000095573/a-1020000000098176
至于后面那个为啥错误的… 这个还需要说明么… 判断相等首要的因素是内容要相等,只是 ==
非严格模式会帮我们自动将两者的类型转换成一致的而已。字符串内容都不同你到底是为啥会觉得相等的…
你理解错了。
比较运算符直接的转换 是:整数和字符串比较,字符串转为整数,那么字符串sdfsdf就转为整数0了,所以第三条是true。
第四条是true因为他们都是字符串,所以就直接比较了,那么字符串0和sdfsf自然不等,为false
==
比较只比较值,不同类型会转换为同一类型比较。
要比较类型用===
,必须值和类型都一样才为true。
这些官方文档里都有写的,请仔细阅读文档。
var_dump(0=='sdfsdf');
弱类型比较通常会先进行类型转换转为相同类型在进行值相等判断.
其中字符串和数值的比较规则是字符串转换成数字. 所以上面那个比较实际的进行可看作
var_dump(0 == (int)'sdfsdf');
var_dump('0'=='sdfsf');
两个都是字符串就是比较值是否相等.
字符串和数字关键后会被转换成0,这样的现象在数据库中也会存在的
http://php.net/manual/zh/language.operators.comparison.php
如果比较一个数字和字符串或者比较涉及到数字内容的字符串,
则字符串会被转换为数值并且比较按照数值来进行.此规则也适用于switch语句.
当用===或!==进行比较时则不进行类型转换,因为此时类型和数值都要比对.
PHP中字符串跟数字比较时,字符串会被转化为数字后进行比较,转化过程类似intval():
<code>echo intval('5stars'); 输出5 print_r('5stars'==5); 输出1 var_dump('5stars'==5); 输出bool(true) var_dump('5stars'===5); 输出bool(false) var_dump('0e1'=='0e2'); 输出bool(true) var_dump('0e1'==='0e2'); 输出bool(false) </code>
PHP中比较字符串应该用恒等于===或者strcmp.

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