Changing a global variable from inside a function

问题:

I am trying to change a variable that is outside of a function, from within a function. Because if the date that the function is checking is over a certain amount I need it to change the year for the date in the beginning of the code.

$var = "01-01-10";
function checkdate(){
     if("Condition"){
            $var = "01-01-11";
      }
}

回答1:

A. Use the global keyword to import from the application scope.

$var = "01-01-10";
function checkdate(){
    global $var;  
    if("Condition"){
        $var = "01-01-11";
    }
}
checkdate();

B. Use the $GLOBALS array.

$var = "01-01-10";
function checkdate(){
    if("Condition"){
        $GLOBALS['var'] = "01-01-11";
    }
}
checkdate();

C. Pass the variable by reference.

$var = "01-01-10";
function checkdate(&$funcVar){  
    if("Condition"){
        $funcVar = "01-01-11";
    }
}
checkdate($var);

回答2:

Just use the global keyword like so:

$var = "01-01-10";
function checkdate(){
     global $var;

     if("Condition"){
            $var = "01-01-11";
      }
}

Any reference to that variable will be to the global one then.

回答3:

All the answers here are good, but... are you sure you want to do this?

Changing global variables from within functions is generally a bad idea, because it can very easily cause spaghetti code to happen, wherein variables are being changed all over the system, functions are interdependent on each other, etc. It's a real mess.

Please allow me to suggest a few alternatives:

1) Object-oriented programming

2) Having the function return a value, which is assigned by the caller.

e.g. $var = checkdate();

3) Having the value stored in an array that is passed into the function by reference

function checkdate(&$values) { if (condition) { $values["date"] = "01-01-11"; } }

Hope this helps.

回答4:

Try this pass by reference

  $var = "01-01-10";
    function checkdate(&$funcVar){  
        if("Condition"){
            $funcVar = "01-01-11";
        }
    }
    checkdate($var);

or Try this same as the above, keeping the function as same.

 $var = "01-01-10";
    function checkdate($funcVar){  
        if("Condition"){
            $funcVar = "01-01-11";
        }
    }
    checkdate(&$var);