is_null versus isset [vs. empty vs. isnan]

arianhojat

hello i was wondering when to check for each.
for example, is one better suited to a specific purpose?

maybe like when u submit a form.
if( !is_null(_$POST['submit']) ) //or should i use isset?
{
do_stuff();
}

how about checking for NULL for values returned by a database row.
if( !is_null($row['field']) )
echo "not null value: $row['field']";

Also I remember in ASP/JSP checking to see whether a variable is not null AND is set or not equal to empty string. i forget why this was done, if anyone wants to elaborate on examples where this type of example is useful. something that looks like...
if( !is_null($GET['blah']) && !empty($GET['blah']) )
echo "good value?";

i think in ASP i was checking for null beforehand to see if the variable wasn't set to anything yet and cehcking for the empty string wouldnt shortcircuit an error.

laserlight

Use isset or empty for incoming variables before processing them further.

devinemke

arianhojat wrote:
maybe like when u submit a form.
if( !is_null(_$POST['submit']) ) //or should i use isset?
{
do_stuff();
}

it all depends. if the incoming POST element you are checking is an empty text box then [man]is_null[/man] would return FALSE since an empty string is not NULL. if the POST element is an unchecked checkbox then [man]is_null[/man] would return TRUE because an unset variable is NULL, but be advised that you will get an "Undefined variable" error if you are checking for a variable that does not exist (depending on your error reporting settings).

arianhojat wrote:
how about checking for NULL for values returned by a database row.
if( !is_null($row['field']) )
echo "not null value: $row['field']";

NULL has special meaning in database values. if the field you are checking is allowed to be set to NULL (at table creation) and the row you are checking is in fact NULL then [man]is_null[/man] would return TRUE.

read up on NULL.

Installer

There are some helpful tables here.

arianhojat

thanx! info and table is useful