问题
I have (or not) a variable $_GET['myvar'] coming from my query string and I want to check if this variable exists and also if the value corresponds to something inside my if statement:
What I'm doing and think is not the best way to do:
if(isset($_GET['myvar']) && $_GET['myvar'] == 'something'): do something
My question is, exist any way to do this without declare the variable twice?
That is a simple case but imagine have to compare many of this $myvar variables.
回答1:
Sadly that's the only way to do it. But there are approaches for dealing with larger arrays. For instance something like this:
$required = array('myvar', 'foo', 'bar', 'baz');
$missing = array_diff($required, array_keys($_GET));
The variable $missing now contains a list of values that are required, but missing from the $_GET array. You can use the $missing array to display a message to the visitor.
Or you can use something like that:
$required = array('myvar', 'foo', 'bar', 'baz');
$missing = array_diff($required, array_keys($_GET));
foreach($missing as $m ) {
$_GET[$m] = null;
}
Now each required element at least has a default value. You can now use if($_GET['myvar'] == 'something') without worrying that the key isn't set.
Update
One other way to clean up the code would be using a function that checks if the value is set.
function getValue($key) {
if (!isset($_GET[$key])) {
return false;
}
return $_GET[$key];
}
if (getValue('myvar') == 'something') {
// Do something
}
回答2:
If you're looking for a one-liner to check the value of a variable you're not sure is set yet, this works:
if ((isset($variable) ? $variable : null) == $value) { }
The only possible downside is that if you're testing for true/false - null will be interpreted as equal to false.
回答3:
As of PHP7 you can use the Null Coalescing Operator ?? to avoid the double reference:
$_GET['myvar'] = 'hello';
if (($_GET['myvar'] ?? '') == 'hello') {
echo "hello!";
}
Output:
hello!
In general, the expression
$a ?? $b
is equivalent to
isset($a) ? $a : $b
回答4:
As mellowsoon suggest, you might consider this approach:
required = array('myvar' => "defaultValue1", 'foo' => "value2", 'bar' => "value3", 'baz' => "value4");
$missing = array_diff($required, array_keys($_GET));
foreach($missing as $key => $default ) {
$_GET[$key] = $default ;
}
You put the default values and set the not recieved parameters to a default value :)
回答5:
My question is, exist any way to do this without declare the variable twice?
No, there is no way to do this correctly without doing two checks. I hate it, too.
One way to work around it would be to import all relevant GET variables at one central point into an array or object of some sort (Most MVC frameworks do this automatically) and setting all properties that are needed later. (Instead of accessing request variables across the code.)
回答6:
Thanks Mellowsoon and Pekka, I did some research here and come up with this:
- Check and declare each variable as null (if is the case) before start to use (as recommended):
!isset($_GET['myvar']) ? $_GET['myvar'] = 0:0;
*ok this one is simple but works fine, you can start to use the variable everywhere after this line
- Using array to cover all cases:
$myvars = array( 'var1', 'var2', 'var3');
foreach($myvars as $key)
!isset($_GET[$key]) ? $_GET[$key] =0:0;
*after that you are free to use your variables (var1, var2, var3 ... etc),
PS.: function receiving a JSON object should be better (or a simple string with separator for explode/implode);
... Better approaches are welcome :)
UPDATE:
Use $_REQUEST instead of $_GET, this way you cover both $_GET and $_POST variables.
!isset($_REQUEST[$key]) ? $_REQUEST[$key] =0:0;
回答7:
why not create a function for doing this, convert the variable your want to check into a real variable, ex.
function _FX($name) {
if (isset($$name)) return $$name;
else return null;
}
then you do _FX('param') == '123', just a thought
回答8:
I use all time own useful function exst() which automatically declare variables.
Example -
$element1 = exst($arr["key1"]);
$val2 = exst($_POST["key2"], 'novalue');
/**
* Function exst() - Checks if the variable has been set
* (copy/paste it in any place of your code)
*
* If the variable is set and not empty returns the variable (no transformation)
* If the variable is not set or empty, returns the $default value
*
* @param mixed $var
* @param mixed $default
*
* @return mixed
*/
function exst( & $var, $default = "")
{
$t = "";
if ( !isset($var) || !$var ) {
if (isset($default) && $default != "") $t = $default;
}
else {
$t = $var;
}
if (is_string($t)) $t = trim($t);
return $t;
}
回答9:
A solution that I have found from playing around is to do:
if($x=&$_GET["myvar"] == "something")
{
// do stuff with $x
}
回答10:
<?php
function myset(&$var,$value=false){
if(isset($var)):
return $var == $value ? $value : false;
endif;
return false;
}
$array['key'] = 'foo';
var_dump(myset($array['key'],'bar')); //bool(false)
var_dump(myset($array['key'],'foo'));//string(3) "foo"
var_dump(myset($array['baz'],'bar'));//bool(false)
回答11:
This is similar to the accepted answer, but uses in_array instead. I prefer to use empty() in this situation. I also suggest using the new shorthand array declaration which is available in PHP 5.4.0+.
$allowed = ["something","nothing"];
if(!empty($_GET['myvar']) && in_array($_GET['myvar'],$allowed)){..}
Here is a function for checking multiple values at once.
$arrKeys = array_keys($_GET);
$allowed = ["something","nothing"];
function checkGet($arrKeys,$allowed) {
foreach($arrKeys as $key ) {
if(in_array($_GET[$key],$allowed)) {
$values[$key];
}
}
return $values;
}
回答12:
Well, you could get by with just if($_GET['myvar'] == 'something') since that condition presumes that the variable also exists. If it doesn't, the expression will also result in false.
I think it's ok to do this inside conditional statements like above. No harm done really.
回答13:
No official reference but it worked when I tried this:
if (isset($_GET['myvar']) == 'something')
来源：https://stackoverflow.com/questions/4007752/php-check-if-variable-exist-but-also-if-has-a-value-equal-to-something