pelicin › prog › C++

The auto Type

You can use the auto type to let the compiler infer a variable's type based on its initializer. (Introduced in C++20.)

Basic example

You have to initialize variables with type auto.

// `5.0` is a double literal,
// so `my_double` will be type double
auto my_double = 5.0;

// `1 + 2` evaluates to an int,
// so `my_int` will be type int
auto my_int = 1 + 2;

// `my_int` is an int,
// so `my_number` will be type int too
auto my_number = my_int;

Example with pointers and references

You can use auto with pointers and references too.

// auto = int
auto year = 2009;

// auto* = int*
auto* year_ptr = &year;

// auto& = int&
auto& year_ref = year;

References