[RESOLVED] increment value using $_GET

robkir

I am trying to use a hyperlink to add 1 or subtract 1 from a variable using GET. I'm stuck. It seems so obvious, but... well, you know. Sometimes the obvious isn't.

echo "<a href='".$_SERVER['PHP_SELF'] ."?result=add'> >> </a><br />
<a href='".$_SERVER['PHP_SELF'] ."?result=sub'> << </a><br />";

  if($_GET['result']=="add")   {

  $variable++;
  }

  else if($_GET['result']=="sub")   {

  $variable--;

  }

  echo "User choice " . $variable;

traq

You've got the right idea with the GET params, but in the code you posted, [font=monospace]$variable[/font] does not exist before you try to use it. It will be initialized as NULL, which will be converted to 0 when you try to do math on it, and then result in 1 or -1.

If you're trying to deal with a variable you set on a previous page, then you need to pass it to this page somehow - via the link, or by using sessions, for example. It looks like you might be trying to make pagination links…? you could simply do the math beforehand:

<?php

// current page is page #2
$current = 2;

print "<a href=?result=".$current + 1.">»</a><br>" // results in "?result=3"
   ."<a href=?result=".$current - 1.">«</a><br> ";  // results in "?result=1"

You should also know that using [font=monospace]PHP_SELF[/font] (without escaping the value, as you show above) will create a cross-site scripting vulnerability.

robkir

Hi traq,

My program does not like $current + 1 in the hyperlink. Is there something else I need to do?

Thanks for the alert on PHP_SELF. When you say escape the value, where do I do that? Or, is it better just to do as you have done with <a href=?...> and leave the destination page off entirely when it is call itself.

robkir

traq

robkir;11037741 wrote:
My program does not like $current + 1 in the hyperlink. Is there something else I need to do?

What do you mean by "does not like"?

robkir;11037741 wrote:
Thanks for the alert on PHP_SELF. When you say escape the value, where do I do that? Or, is it better just to do as you have done with <a href=?...> and leave the destination page off entirely when it is call itself.

If you are linking to the same page, with just a different query string, then yes, you can simply leave the path out and start with the ?.

If you want to use PHP_SELF (or any other user-supplied data you wish to print), you can use [man]htmlentities[/man] to make sure you don't print anything malicious on your page (it might still break things, but it will defeat the potential attack).

robkir

What do you mean by "does not like"?

I should have been clearer. The '$current + 1' seems to be the problem. It prevents the php from running.

Thanks

traq

robkir;11037753 wrote:
I should have been clearer. The '$current + 1' seems to be the problem. It prevents the php from running.

Meaning you see a blank white screen? Enable error reporting in your php.ini file:

error_reporting = E_ALL | E_STRICT
display_errors = On

In this case, I forgot to wrap the expression in parenthesis:

<?php 

// current page is page #2 
$current = 2; 

print "<a href=?result=".($current + 1).">»</a><br>" // results in "?result=3" 
   ."<a href=?result=".($current - 1).">«</a><br> ";  // results in "?result=1"

robkir

Enable error reporting in your php.ini file:

error_reporting = E_ALL | E_STRICT[/QUOTE]
I am relying on my hosting company to provide php. I checked their phpinfo and error checking is off. They don't like to make changes...so I doubt if they would be willing to change it.

The program no longer crashes...but it still doesn't increment the $current value.


Thanks for staying with me on this. I'd like to get it to work. The rest of the program seems to be working flawlessly...only this piece is the problem.

traq

robkir;11037759 wrote:
I am relying on my hosting company to provide php. I checked their phpinfo and error checking is off. They don't like to make changes...so I doubt if they would be willing to change it.

Unfortunate. Have you tried adding your own php.ini file?
Of course, you can always install a LAMP stack at home and develop locally… 🙂

robkir;11037759 wrote:
doesn't increment the $current value.

To clarify, I was making an example of something else: that you didn't need to pass the values between pages at all. But let's go back to your original code:

<?php

// set the variable:
//    first, look for the value passed in the query string (see below)
if( isset( $_GET["variable"] ) && isset( $_GET["result"] ) ){
    $variable = $_GET["variable"];
    // also do the add/sub math
    if( $_GET["result"] === "add" ){ $variable++; }
    if( $_GET["result"] === "sub" ){ $variable--; }
}
//    otherwise, set a default value
$variable = 1;

echo "User choice " . $variable;  

// in the links, pass not only "add" or "sub",
//    but also the value of your variable
print "<a href=?variable=$variable&result=add>»</a>"
    ."<a href=?variable=$variable&result=sub>«</a>";

robkir

By jove....it works. I appreciate the effort, thanks for helping me solve it.

As for installing php, perhaps I sound like a wimp, but I've got so many things on the proverbial plate, that I am taking the easy way out by having the host handle to details. Besides, its got to run on their server, so if my php configuration is different, it might be a problem.

traq

robkir;11037771 wrote:
By jove....it works. I appreciate the effort, thanks for helping me solve it.

no problem.

robkir;11037771 wrote:
As for installing php, perhaps I sound like a wimp, but I've got so many things on the proverbial plate, that I am taking the easy way out by having the host handle to details.

Easier than you think. Also, to be clear, I'm recommending a development server, not self-hosting.

robkir;11037771 wrote:
Besides, its got to run on their server, so if my php configuration is different, it might be a problem.

It's not difficult to match versions and configurations.

I understand if it's not something you are interested in / have time for. But it's fun and has lots of (unimaginable!) benefits, should you ever become ready for it. It is a huge boon to productivity.

robkir

Goods points...plus I have to do some traveling. Might be easier to have my own development server than trying to find a secure internet connection.