what does eval() do?

[jdc44]

Happy Easter all,
I'm an experienced php programmer, but I must confess, I do not understand what eval does. I've read its php manual page, but I still remain confused.

I have a bit of code I inherited. It uses eval in a spot like so.

while ( $row=$results->fetchRow(DB_FETCHMODE_ASSOC) ){
[INDENT]$name = "maid$row[MA_ID]"; // example: $name = 'maid55'
eval("\$name = \$$name;");
if ( $name == 1 ){
[INDENT]// rest of code[/INDENT]
}[/INDENT]
}

What is the eval statement doing in the code snippet above? What (in simple english) does the eval() do?

Thanks for explaining.

Stumped!

[laserlight]

eval() takes a string argument and evaluates it as PHP code. Consequently, it can lead to potential security problems, and almost never needs to be used. The code snippet you gave shows a misuse of eval(). It can be more simply written:

while ( $row=$results->fetchRow(DB_FETCHMODE_ASSOC) ){

$name = "maid$row[MA_ID]"; // example: $name = 'maid55'
$name = $$name;
if ( $name == 1 ){

    // rest of code

}

}

But now, the above code shows an unnecessary use of variable variables. It would be better for $maid to be an array, upon which one can write:

while ( $row=$results->fetchRow(DB_FETCHMODE_ASSOC) ){

// Assuming MA_ID is not a defined constant, but a string index.
if ( $maid[$row['MA_ID']] == 1 ){

    // rest of code

}

}