if-statement

safra

Hi,

In a php/mysql script I am using there is a table column options (smallint).

In php if-statement are used that look like this:

if($row[options] & 128){

}

where $row[options] is the table column.

Can anyone explain to me how to interprete this kind of if-statement?

Thanks,
Raoul

goh_gss

if statement will perform when the condition is true.

e.g.

if (a)
{
x=y

}

if (a)= true, then will access the x=y, else nothing will perform.

safra

Sorry for the late reply,

I understand the basics of an if-statement, just not this kind of if-statement.

Let me explain a little bit more.

The specific MySQL column options holds a value. This value is the sum of a number of form option that can be selected. These form options look like this (look how the values are built up).

<INPUT TYPE="checkbox" NAME="showemail" VALUE="1">
<INPUT TYPE="checkbox" NAME="showbirthday" VALUE="2">
<INPUT TYPE="checkbox" NAME="showhomepage" VALUE="4">
<INPUT TYPE="checkbox" NAME="online"VALUE="8">
<INPUT TYPE="checkbox" NAME="notifications" VALUE="16">

Example:
the 1st and last checkbox are checked.

the value of column options will be:
$showemail + showbirthday + showhomepage + online + notifications = 17

the if-statement:
if($row[options] & 128){
}

will return false. but,

if($row[options] & 16){
}

will return true (16 is the equivalent of checkbox 'notifications').

What I am trying to find out is how to interprete this kind of if-statement ($row[options] & 16) what does the '& 16' part exactly mean?

Thanks,
Raoul

Weedpacket

& is the bitwise AND operator. Convert its two arguments into binary, then the first bit of the result is the AND of the first bits of the arguments, the second bit of the result is the AND of the second bits, etc.

http://www.php.net/manual/en/language.operators.bitwise.php

So ($foo & 16) is true (more precisely, nonzero, which amounts to the same thing) if the fifth-to-last bit in $foo is set (because the fifth-to-last bit in 16 = 10000b is set).

safra

Thanks weedpacket, I think I know understand how this works.

Raoul