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C++ High Performance

Using auto for Variables

Learn how to use the auto keyword when declaring variables.

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Using the auto keyword for variable declarations

The introduction of the auto keyword in C++11 has initiated quite a debate among C++ programmers. Many people think it reduces readability, or even that it makes C++ similar to a dynamically typed language. We can (almost) always use auto as it makes the code safer and less littered with clutter.

Note: Overusing auto can make the code harder to understand. When reading code, we usually want to know which operations are supported by some object. A good IDE can provide us with this information, but it’s not explicitly there in the source code.

We can use auto for local variables using the left-to-right initialization style. This means keeping the variable on the left, followed by an equals sign, and then the type on the right side, like this:

C++ 17
auto i = 0;
auto x = Foo{};
auto y = create_object();
auto z = std::mutex{}; // OK since C++17

With guaranteed copy elision introduced in C++17, the ...