dongtan8532 2019-06-23 10:30 采纳率: 0%
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PHP字符串表达式错误:这里发生了什么?

The expression

"a".(strlen('ab')-strlen('a')) 

evaluates to a1 as expected.

But if I accidentally omit parentheses,

"a".strlen('ab')-strlen('a') 

evaluates to -1. What is happening here?

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  • douzou8074 2019-06-23 11:01
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    I guess you might also get a Warning for non-numeric value when you omit the "()".

    As a normal mathematical rule, the brackets are solved first so in the

    "a".(strlen('ab')-strlen('a'))
    

    strlen('ab') is 2 and, strlen('a') is 1, so 2-1= 1 and it gets concated with 'a' so becomes 'a1'.

    And when you remove the parentheses,

    "a".strlen('ab')-strlen('a') 
    

    then it executes left to right so

    1. strlen('ab') concate's with 'a' which gives a2
    2. then 'a2' which is non-numeric is substracted with strlen('a') which is 1. so warning is displayed.
    3. But 'a2' is forced to be converted to numeric, thus becomes 0 so finally
    4. 0 - 1 = -1
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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