Do not understand how this array result happens

Question

I'm trying to learn to build a login sequence. In one part, I wanted to determine if the user left any of the 3 required fields blank:

foreach ( $_POST as $key => $value )
   {
      if ( $key = "school_code" ||
           $key = "user_name"   ||
           $key = "password" )
         {
            if ( $value == "" )
               {
                  $a_blank[] = $key ;
               }  
         }  
   }

if( @sizeof( $a_blank ) > 0 )
   {
      echo '<pre>';
      print_r( $a_blank );
      echo '</pre>';
   }

If the user does not enter anything for school_code or user_name, but DOES enter a password and then clicks submit, the result is:

Array
(
    [0] => 1
    [1] => 1
)

Why isn't the array result like this (i.e., the values of $key)?

Array
(
    [0] => school_code
    [1] => user_name
)

Thanks!

Answer 1

Comparison is with ==, not =.

$key = "school_code" || $key = "user_name" || $key = "password"

Should be with == instead. You could write this in a slightly less-verbose way too:

$options = array("school_code","user_name","password");
if (in_array($key, $options) && empty($value)) {
    $a_blank[] = $key;
}

Answer 2

When you're doing a comparison, remember to use two equal signs (==) instead of just one (=). A single equal sign is assignment, two is comparison.

Take this as an example:

$val = false;
if ($val = true)
    foo();

If you use = in the if statement, foo() will be called. What you're actually doing is setting the value of $val to true right inside the if statement. In that case, it will always be true. That's not what you want.

$val = false;
if ($val == true)
    foo();

This is what you want. Here, foo() will not get called.

For more info see the PHP docs.

Answer 3

Two problems with this code.

The

$key = "school_code" || $key = "user_name" || $key = "password" 

Will assign to $key the result of the logical or which will always be true (== 1).

The other problem is that depending on the browser "empty" form values are not always returned so if say the user left password blank it might not appear in the $_POST array.

You would be much better doing a plain old explicit "if"s rather than the fancy array tricks for this.

$missing = array();
foreach (array('school_code','user_name','password') as $nm
if ( !isset($_POST[$nm] length($_POST[$nm]) == 0 ) {
        $missing[] = $nm;
}

Answer 4

I've tried out this code (using the == as comparison of course) and it works fine.

This is the result I got:

Array
(
    [0] => school_code
    [1] => password
)

But when run with the original (mistakenly using the = sign) it returns:

Array
(
    [0] => 1
    [1] => 1
)

The problem is that the asker is using = to compare instead of ==. So the solution is to use == and it will work.

Can anyone explain this?

Answer 5

Thanks for all the help with my question! I'm frustrated that the "==" vs "=" has tripped me up yet once again. Wish I could set my IDE so that every time I typed an equal sign, a little popup would ask me, "ARE YOU SURE?"

FWIW, here is the HTML:

<?php
session_start() ;
$_SESSION["form_token"] = md5( rand( time(), true ) ) ;
?>

<!-- Display login form -->
<div id="login">
<p>Please supply your username, 3-digit school code, and password.</p>

<form action = "<?php echo $_SERVER['PHP_SELF']; ?>"
      method = "post">

<Input type = "hidden"
       name = "form_token"
      value = "<?php echo $_SESSION['form_token']; ?>" />

<dl>
<dt><strong>Username</strong></dt>
<dd><input type = "text"
           name = "user_name" /></dd><br/>

<dt><strong>School code</strong></dt>
<dd><input type = "text"
           name = "school_code" /></dd><br/>

<dt><strong>Password</strong></dt>
<dd><input type = "password"
           name = "password" /></dd> <br/>

<dd><input type = "submit"
           name = "action"
           value = "Login" /></dd>
</dl>
</form>

Answer 6

when you are using such comapring if ( $key == "school_code" || .. )

you may have such bug if you wrongly type "=" instead "=="

nice trick is use it that way : if ("school_code" == $key || ... and you'll never has this bug because another way it would be error

sorry for bad english.