PHP替代if（！isset（…））{…} => GetVar（$ Variable，$ ValueIfNotExists）

Question

When I use a variable in PHP which does not exist , I will get a warning/error message.

Notice: Undefined variable

So usually I'm writing an if-statement to initialize it first.

Example 1:

if (!isset($MySpecialVariable))
{
  $MySpecialVariable = 0;
}
$MySpecialVariable++;

Example 2:

if (!isset($MyArray["MySpecialIndex"]))
{
  $MyArray["MySpecialIndex"] = "InitialValue";
}
$Value = $MyArray["MySpecialIndex"];

The disadvantage is that I have to write $MySpecialVariable or $MyArray["MySpecialIndex"] several times and the program gets bloated.

How can I achieve the same result with writing the variable only once ?

I'm looking for something like

GetVar($MySpecialVariable, 0); # Sets MySpecialVariable to 0 only if not isset()
$MySpecialVariable++;

$Value = GetVar($MyArray["MySpecialIndex"], "InitialValue");

Answer 1

function GetVar(&$MyVar, $ValueIfVarIsNotSet)
{
    $MyVar = (isset($MyVar)) ? $MyVar : $ValueIfVarIsNotSet;
    return $MyVar;
}

The key is to to pass the requested variable by reference ( &$MyVar ). Otherwise it is not possible to call a function with a possibly uninitialized variable.

Test code:

echo "<pre>";

unset($a);
$b = "ValueForB";
unset($c);
$d = "ValueForD";

echo (isset($a)) ? "a exists" : "a NotSet";
$a = GetVar($a, 7); # $a can be passed even if it is not set here
$a++;
echo "\nValue=$a\n";
echo (isset($a)) ? "a exists" : "a NotSet";
echo "\n\n";

echo (isset($b)) ? "b exists" : "b NotSet";
echo "\nValue=".GetVar($b, "StandardValue2")."\n";
echo (isset($b)) ? "b exists" : "b NotSet";
echo "\n\n";

echo (isset($c)) ? "c exists" : "c NotSet";
echo "\nValue=".GetVar($c, "StandardValue3")."\n";
echo (isset($a)) ? "c exists" : "c NotSet";
echo "\n\n";

echo (isset($d)) ? "d exists" : "d NotSet";
echo "\nValue=".GetVar($d, "StandardValue4")."\n";
echo (isset($d)) ? "d exists" : "d NotSet";
echo "\n\n";

echo "</pre>";

Output:

a NotSet
Value=8
a exists

b exists
Value=ValueForB
b exists

c NotSet
Value=StandardValue3
c exists

d exists
Value=ValueForD
d exists

Answer 2

When you are running PHP7 you can use the null coalescing operator
Like:

$myVar = $myVar ?? 0;