Automatic Type Deduction: decltype

decltype vs auto

The decltype keyword was also introduced in C++11, though its functionality differs from auto. decltype is used to determine the type of an expression or entity.

Here is the correct format:

decltype(expression) 

We can use auto to create variables, but decltype returns the type of an expression containing variables.

Rules

• If the expression is an lvalue, decltype will return a reference to the data type of the expression

• If the expression is an rvalue, decltype will return the data type of the value