Solution to Notice: Undefined index error message in php

if(array_key_exists( 'istrue',$_POST))
{
if($_POST[ 'istrue'])
{
$istrue=$_POST[ 'istrue'];
}
}else{
$istrue='';
}

The subsequent judgment can be as follows

elseif ($istrue == 'ok')

to avoid such errors. You can refer to how to do some program systems. For details, please refer to the code of dedecms or phpcms.

//Check and register externally submitted variables
foreach($_REQUEST as $_k=>$_v)
{
if( strlen($_k)> ;0 && eregi('^(cfg_|GLOBALS)',$_k) )
{
exit('Request var not allow!');
}
}
function _RunMagicQuotes(&$svar)
{
if(! get_magic_quotes_gpc())
{
if( is_array($svar) )
{
foreach($svar as $_k => $_v) $svar[$_k] = _RunMagicQuotes($_v);
}
else
{
$svar = addslashes($svar);
}
}
return $svar;
}
foreach(Array('_GET','_POST','_COOKIE') as $_request )
{
foreach($$_request as $_k => $_v) ${$_k} = _RunMagicQuotes($_v);
}
if(empty($istrue))
{
$istrue = '';
}