Special characters and symbol problem

[squiblo]

If a user enters data into an input field, i do not want them to be able to upload special characreters like the following or numbers:

 

• "- #'][{}£$%^&*()â▀♣
  

 

and many more from character map.

 

how can i do this, by checking a variable like...

 

$username = $_POST['username'];

 

Thanks.

[mapleleaf]

Can you manage letters only??

 

function alpha_only($string)

    {

        return (preg_match("/[A-Z\s_]/i", $string) > 0) ? true : false;

    }

[squiblo]

what exactly will that function do, because i need an else saying something like, "You can only use letters"

[mapleleaf]

exactly only allows letters.

 

If it is usernames you are doing you could use this php function:

ctype_alnum  ( string $text  )

Check the maual http://php.net/manual/en/function.ctype-alnum.php

[Psycho]

Can you manage letters only??

 

function alpha_only($string)

    {

        return (preg_match("/[A-Z\s_]/i", $string) > 0) ? true : false;

    }

 

That function will not work. It simply returns true if ANY ONE character matches the pattern! The pattern needs to be exclusionary (Besides, why would you test if something is true, just to return true or false? Just return the result of the test. See example below)

 

function validCharacters($input)
{
    //Returns true if all the characters are letters (upper and lower case)
    return (preg_match("/[^\w]/", $input)==0);
}

//Usage
if (!validCharacters($_POST['username']))
{
  echo "Username can only contain letters";
}
else
{
  //Input was valid
}

[squiblo]

The following function only works for the variable "$forname" how can i get it to also work for $surname and $city

 

function validCharacters($input)
   {
      //Returns true if all the characters are letters (upper and lower case)
      return (preg_match("/[^\w]/", $input)==0);
   }

   //Usage
   if (!validCharacters($forname)+($surname)+($city))
    {
      echo "All boxes can only contain letters";
    }
      else
   {
      echo "success";
   }

[Psycho]

Typically you would validate each field individually and give the user specific details about what fields need to be changed, but if you want to do it all in one go, then use the correct method for concatenating string - which is a period:

 

if (!validCharacters($forname.$surname.$city))

[squiblo]

Thank you everyone!