UnityEngine.Vector3 is not marked as Serializable

Guide for serializing Vector3 data in Unity.

When attempting to save a Vector3 variable's value (or a Quaternion for that matter) to disk, you may find that Unity will throw a UnityEngine.Vector3 is not marked as Serializable error. To work around this, you can create a new SerializedVector struct that can be used to serialize your Vector3 and saved to disk.

Create a new C# script in Unity called SerializedVector3 and enter the following code:

using UnityEngine;
[System.Serializable]

public struct SerializedVector3
 {
 public float x;
 public float y;
 public float z;

 public SerializedVector3(float x, float y, float z)
 {
   this.x = x;
   this.y = y;
   this.z = z;
 }

 public SerializedVector3(Vector3 v)
 {
 this.x = v.x;
 this.y = v.y;
 this.z = v.z;
 }

 public override bool Equals(object obj)
 {
   if ((obj is SerializedVector3) == false){
   return false;
   }

   var s = (SerializedVector3)obj;
   return x == s.x && y == s.y && z == s.z;
 }

 public override int GetHashCode()
 {
   var hashCode = 373119288;
   hashCode = hashCode * -1521134295 + x.GetHashCode();
   hashCode = hashCode * -1521134295 + y.GetHashCode();
   hashCode = hashCode * -1521134295 + z.GetHashCode();
   return hashCode;
 }

 public Vector3 ToVector3()
 {
   return new Vector3(x, y, z);
 }

 public static bool operator == (SerializedVector3 a, SerializedVector3 b)
 {
   return a.x == b.x && a.y == b.y && a.z == b.z;
 }

 public static bool operator != (SerializedVector3 a, SerializedVector3 b)
 {
   return a.x != b.x || a.y != b.y || a.z != b.z;
 }

 public static implicit operator Vector3(SerializedVector3 x)
 {
   return new Vector3(x.x, x.y, x.z);
 }

 public static implicit operator SerializedVector3(Vector3 x)
 {
   return new SerializedVector3(x.x, x.y, x.z);
 }

}

To use the serialized Vector3, call it's constructor passing in a Vector3, for example:

...
public Vector3 GetCheckPointPosition()
 {
 return checkpointPosition;
 
 }
 
checkpointPosition = new SerializedVector3(GetCheckPointPosition());

References

https://answers.unity.com/questions/1693694/serializationexception-end-of-stream-encountered-b.html

https://forum.unity.com/threads/vector3-is-not-marked-serializable.435303/