Any way to use a var within a predefined var?

Donny Bahama · #1 May 8th, 2007, 22:56

This doesn't work: $_SESSION[$var]

Is there some workaround that does. I've looked into $$vars (man, those were tough to wrap my brain a round at first!) but I don't see how they could help me. I also tried wrapping the inner var in curly brackets; that didn't work either.

masonbarge · #2 May 10th, 2007, 16:46

I'm not quite sure what you're getting at. Maybe this will get you started.
Page 1:

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    $multi=array();
    $multi[0]="This is the first multi";
    $multi[1]=17;
    $_SESSION['multi']=$multi;

Page Two:

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$multi=$_SESSION['multi'];
echo $multi[1];

This works like a charm. You can use an associative array. It retains the cast of the variable values and everything.

On which page do you want to set the variable value? If I'm following you at all, you should be able to get the job done by assigning values first and putting them into the superglobal only for transmission.

Donny Bahama · #3 May 10th, 2007, 17:49

What I'm getting at is that I want to pass a variable name (and only the variable name) to a function and have it echo back the variable name and the variable's set value...

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function echoVar(var) {
echo "var=$var";
}

I'd add some string parsing to that function so I could do things like

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// show session var 'return2'
echoVar(SV_return2);
//returns: "$_SESSION['return2'] is set to http://example.com/origination.php"

// show post var 'address'
 echoVar(P_address);
//returns: "$_POST['address'] is set to 1234 Main Street"

// show get var 'sid'
  echoVar(G_sid);
 //returns: "$_GET['sid'] is set to fde58b062cb8391a06df3"
 
 // show Cookie var 'userID'
  echoVar(C_userid)
 //returns: "$_COOKIE['userid'] is set to 1185"

but I don't know how to do that without something like $_SESSION['$var']. It's just a debugging function, but it'd sure be helpful.

masonbarge · #4 May 10th, 2007, 21:15

I think I see what you want.

You could almost surely do this more elegantly using variable variables, but I always pick the easy way. I'm not sure a $$ approach would actually save any coding space.

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function echoVar($type,$name) { 
 if ($type=='S') { $x='$_SESSION'; $value=$_SESSION[$name];
 }elseif ($type=='C') { $x='$_COOKIE'; $value=$_COOKIE[$name];
 }elseif ($type=='P') { $x='$_POST';$value=$_POST[$name];
 }elseif ($type=='G') { $x='$_GET';$value=$_GET[$name];
 }else{
     echo "<br />Improper first argument in EchoVar() for '$name', use S C P or G. <br />";
     return;
 }
   echo '<br />';
   if($value) {
   echo $x . '[\'' . $name . '\'] is set to value ';
   echo $value;
   echo '.<br />';
   }else{
      echo $x . '[\'' . $name . '\'] does not have a value set.';
   }
}

The only trick is not to get stuck trying to express a value for a superglobal inside double quotes. If you have to have EchoVar(SV_username) instead of EchoVar(S, username), my first thought would be to pop a substring replace in the first line or more likely inside the four if's.

masonbarge · #5 May 10th, 2007, 21:35

While I'm at it, if my first try didn't do the trick, this snippet may help you figure out what you want to do. It is really two different approaches.

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foreach ($_SESSION as $k => $v) {
     echo '<br />$_SESSION[' . $k .'] ';
     echo "is set to $v. <br />";
     global $$k;
     echo "$$k has a value of $v. <br />";
 }

I use something like this sometimes with an intro "The following session variables are set".

Donny Bahama · #6 May 11th, 2007, 03:56

Awesome stuff, Mason. Thanks! I'll definitely get use out of that second example, too. I've already created functions ShowPost(), ShowGet() and ShowCookies() based on that code. Great debugging tools!

One quick question regarding the first code you posted...
I "made it my own" as follows:

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function echoVar($type,$name) { 
    if ($type=='S') {
         $var='$_SESSION[\'' . $name . '\']';
        $val=$_SESSION[$name];
    } elseif ($type=='C') {
        $var='$_COOKIE[\'' . $name . '\']';
        $val=$_COOKIE[$name];
    } elseif ($type=='P') {
        $var='$_POST[\'' . $name . '\']';
        $val=$_POST[$name];
    } elseif ($type=='G') {
        $var='$_GET[\'' . $name . '\']';
        $val=$_GET[$name];
    } elseif ($type=='N') {
        $var='(basic var) $'. $name;
        $val=$name;
    } else {
        echo "<br />Improper first argument in EchoVar() for '$name', use<br>S (SESSION), C (COOKIE), P (POST), G (GET) or N (none = plain var). <br />";
        return;
    }
    if($val) {
        echo $var.' is set to '.$val.'<br />';
    }else{
        echo $var . ' does not have a value set.<br />';
    }
}

Notice the "type=N" section? That doesn't work. I tried using $$name (I really don't get variable variables!) but that doesn't work either. What can I use there that would work?
Thanks so much for the help!

masonbarge · #7 May 11th, 2007, 14:00

$$'s -- I sympathize. It helps me to fixate on the fact that I'm naming a variable, not setting a value, then remember that when I see or use one I have to expect to take two mental steps, not one. If it really bugs you, just try setting all your variables like this for a day or two.

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$grimx='var';
$$grimx=round($result, 2); or whatever

EchoVar won't work for a plain variable because you can't enter both a variable name and a variable value into the $name argument. You are just going to get "username has a value of username" or "Bob has a value of Bob" depending on whether you enter "username" or "$username" as the argument.

Using $$ is just going to rename the variable to the value of $name. It's the wrong direction. I can't think of an easy fix. If someone knows how to do this, please chime in.

You can add an optional third optional argument $var which is going to get rather silly -- you'd be using it like:

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echoVar(N, username, $username);

or you could simply make another function. IIRC you can't conditionally define functions with the same name - the "if" clauses have to go inside the function definition. So you can't define EchoVar two different ways depending on whether the variable is an array or a simple.

If you want a more complex function definition, you might be able to set up the function you want by using variable parameters. I've never done it so I don't know how to do it or whether it would even get you where you want to go. It looks like kind of a pain but it would be fun.

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Any way to use a var within a predefined var?