---
uid: input-system-step-1-state-struct
---

# Step 1 The state struct

The first step is to create a C# `struct` that represents the form in which the system receives and stores input, and also describes the `InputControl` instances that the Input System must create for the Device in order to retrieve its state.

```CSharp
// A "state struct" describes the memory format that a Device uses. Each Device can
// receive and store memory in its custom format. InputControls then connect to
// the individual pieces of memory and read out values from them.
//
// If it's important for the memory format to match 1:1 at the binary level
// to an external representation, it's generally advisable to use
// LayoutLind.Explicit.
[StructLayout(LayoutKind.Explicit, Size = 32)]
public struct MyDeviceState : IInputStateTypeInfo
{
    // You must tag every state with a FourCC code for type
    // checking. The characters can be anything. Choose something that allows
    // you to easily recognize memory that belongs to your own Device.
    public FourCC format => new FourCC('M', 'Y', 'D', 'V');

    // InputControlAttributes on fields tell the Input System to create Controls
    // for the public fields found in the struct.

    // Assume a 16bit field of buttons. Create one button that is tied to
    // bit #3 (zero-based). Note that buttons don't need to be stored as bits.
    // They can also be stored as floats or shorts, for example. The
    // InputControlAttribute.format property determines which format the
    // data is stored in. If omitted, the system generally infers it from the value
    // type of the field.
    [InputControl(name = "button", layout = "Button", bit = 3)]
    public ushort buttons;

    // Create a floating-point axis. If a name is not supplied, it is taken
    // from the field.
    [InputControl(layout = "Axis")]
    public short axis;
}
```

The Input System's layout mechanism uses [`InputControlAttribute`](xref:UnityEngine.InputSystem.Layouts.InputControlAttribute) annotations to add Controls to the layout of your Device. For details, see the [layout system](layouts.md) documentation.

With the state struct in place, you now have a way to send input data to the Input System and store it there. The next thing you need is an [`InputDevice`](xref:UnityEngine.InputSystem.InputDevice) that uses your custom state struct and represents your custom Device.