Set the type of variable var to type.
Possibles values of type are:
"boolean" (or, since PHP 4.2.0, "bool")
"integer" (or, since PHP 4.2.0, "int")
"float" (only possible since PHP 4.2.0, for older versions use the deprecated variant "double")
"string"
"array"
"object"
"null" (since PHP 4.2.0)
成功回傳TRUE失敗回傳FALSE。
See also gettype(), type-casting and type-juggling.