PHP $ $str in the "$$" of the detailed

This notation is called a mutable variable. Sometimes it is convenient to use variable variable names. That is, the variable name of a variable can be set and used dynamically. An ordinary variable is set by a declaration, for example: $a = "Hello"; ?> Copy Code A mutable variable gets the value of an ordinary variable as the variable name of the variable variable. In the example above, hello uses two dollar sign ($) and can be used as a variable variable. For example: $ $a = "world"; ?> Copy Code At this point, two variables are defined: $a content is "hello" and $hello content is "world". Therefore, it can be expressed as: echo "$a ${$a}"; ?> Copy Code The following wording is more accurate and will output the same result: echo "$a $hello"; ?> Copy Code They all output: Hello world. To use mutable variables with arrays, you must address an ambiguous question. This is when you write the $ $a [1], the parser needs to know if you want to $a [1] as a variable, or you want $ $a as a variable and take out the value of the variable indexed to [1]. The syntax for solving this problem is to use ${$a [1] for the first case, and ${$a}[1 for the second case). The above mentioned is the whole content of this article, I hope you can like.

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