Set the default value for the parameter, but only the last parameter can be omitted. If parameters with default values are placed in the middle, you must leave a comma in the middle to separate them. Here are some examples:

Function getdata($a, $b, $c=0){

....

}

The above paragraph can only give two parameters when calling, and the default value of the third parameter is 0.

Call method: getdata( 1, 1)

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Function getdata($a, $b= 1, $c){

....

}

This paragraph should be called in the middle with a comma, for example: get data (1, 0).

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Function getdata($a, $b=0, $c= 1){

....

}

This part can be called as follows: getdata( 1)