How to avoid undefined index errors

Question

I am working through some code done by a previous developer  I m pretty new to PHP so I am wondering if there is any well known pattern or solution to this problem  Basically the original author does not check any array indexes before he tries to use them  I know I can use isset   to check each before it is used  but right now there are hundreds of lines where these errors are appearing  Before I put on some music and start slamming my head into my keyboard I want to make sure there is not some nice shortcut for handling this  Here is a typical section of code I m looking at         snip     quot text quot    gt   link    top pick marker    output  author      quot  amp nbsp  quot      quot  amp nbsp  quot                                    output  new icon      output  rec labels      quot   amp nbsp   quot                          output  admin link                          output  alternate title                           output  access info                           output  description                           output  url                          output  subject terms                           output  form subdivisions                           output  dates of coverage                            output  update frequency                            output  place terms           snip     I know I can use isset   here for each item  I would have to rearrange things a bit and remove all the concatenation as it is now  Is there any other easy way to do this or am I just stuck with it

User · Answer

You could try using a nice little function that will return the value if it exists or an empty string if not. This is what I use:

function arrayValueForKey($arrayName, $key) {
   if (isset($GLOBALS[$arrayName]) && isset($GLOBALS[$arrayName][$key])) {
      return $GLOBALS[$variable][$key];
   } else {
      return '';
   }
}

Then you can use it like this:

echo ' Values: ' . arrayValueForKey('output', 'admin_link') 
                 . arrayValueForKey('output', 'update_frequency');

And it won't throw up any errors!

Hope this helps!

User · Answer

In my case  I get it worked by defining the default value if the submitted data is empty  Here is what I finally did  using PHP7 3 5    if empty   POST  auto            POST  auto

User · Answer

Same idea as Michael Waterfall  From CodeIgniter      Lets you determine whether an array index is set and whether it has a value     If the element is empty it returns FALSE  or whatever you specify as the default value   function element  item   array   default   FALSE        if     isset  array  item   OR  array  item                       return  default             return  array  item

User · Answer

You can use isset   without losing the concatenation     snip  str    something       isset  output  alternate title       output  alternate title               isset  output  access info       output  access info               etc    You could also write a function to return the string if it is set - this probably isn t very efficient   function getIfSet  amp   var        if  isset  var             return  var            return null      str   getIfSet  output  alternate title      getIfSet  output  access info      etc   You won t get a notice because the variable is passed by reference

User · Answer

A short solution is this  PHP 5 3      output  alternate title      output  alternate title           You get either the value of the variable  if it doesn t evaluate to false  or the false expression   The one after the       Using the ternary Operator  without the  if true  parameter  will return the result of the test expression  The first one   Since undefined evaluates to false  the false expression will be returned    In PHP 7 there is the slightly more elegant Null coalescing operator    output  alternate title      output  alternate title             It would be nice with a default assignment operator like

User · Answer

If you are maintaining old code  you probably cannot aim for  the best possible code ever     That s one case when  in my opinion  you could lower the error reporting level   These  undefined index  should only be Notices   so  you could set the error reporting level to exclude notices   One solution is with the error reporting function  like this       Report all errors except E NOTICE error reporting E ALL   E NOTICE     The good thing with this solution is you can set it to exclude notices only when it s necessary  say  for instance  if there is only one or two files with that kind of code   One other solution would be to set this in php ini  might not be such a good idea if you are working on several applications  though  as it could mask useful notices     see error reporting in php ini   But I insist   this is acceptable only because you are maintaining an old application -- you should not do that when developping new code

User · Answer

foreach  i 0   i lt 10   i          v     array  v            this could help defining  v as an array           is to supress undefined variable  v      array push  v   i

User · Answer

A variation on SquareRootOf2 s answer  but this should be placed before the first use of the  output variable    keys   array  key1    key2    etc     output   array fill keys  keys

User · Answer

Figure out what keys are in the  output array  and fill the missing ones in with empty strings    keys   array keys  output    desired keys   array  author    new icon    admin link    etc      foreach  desired keys as  desired key      if in array  desired key   keys   continue      already set     output  desired key

User · Answer

Set each index in the array at the beginning  or before the  output array is used  would probably be the easiest solution for your case   Example   output  admin link         output  alternate title         output  access info         output  description         output  url            Also not really relevant for your case but where you said you were new to PHP and this is not really immediately obvious isset   can take multiple arguments  So in stead of this   if isset  var1   amp  amp  isset  var2   amp  amp  isset  var3               all are set     You can do   if isset  var1   var2   var3          all are set

[php] How to avoid 'undefined index' errors?

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