PHP: Compare arrays and copy first array value to second array value where second array value is null

How about a foreach() loop:

foreach($array1 as $key=>$value){
    if(!$array2[$key]){
        $array2[$key] = $value;
    }
}

And minimized, but a little less readable:

foreach($array1 as $key=>$value){
    $array2[$key] = $array2[$key] ? $array2[$key] : $value;
}

try this

<?php
$array1 = array( id => '11', c1 => 'abcd', c2 => '4500', c3 => 'texas' ,c4=>'name' );
$array2 = array( id => '12', c1 => '',    c2 => '4500', c3 => 'arizona', c4=>'' );

foreach($array2 as $key =>$value)
{
  if($value == '')
 {
    $array2[$key] = $array1[$key];
 }  
 }  

print_r($array2);
 ?>

Try this :

foreach($array2 as $key=>$value)

if ($value==null) $array2[$key]=$array1[$key];