Checking Whether a Variable Is Set: isset()
Although most functions are covered in Chapter 7, you need to know the isset()
function (literally, "is a variable set?") to make the most of this chapter. To use the function, send it a variable as the only parameter, and it will return true or false depending on whether the variable has a value assigned to it. For example:
$foo = 1; if (isset($foo)) { echo "Foo is set\n"; } else { echo "Foo is not set\n"; } if (isset($bar)) { echo "Bar is set\n"; } else { echo "Bar is not set\n"; }
That will output "Foo is set"
and "Bar is not set"
. Usually if you try to access a variable that isn't set, like $bar
above, PHP will issue a warning that you are trying to use an unknown variable. This does not happen with isset()
, which makes it a safe function to use.
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