October 2005
Intermediate to advanced
372 pages
11h 35m
English
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.