# V3128. The field (property) is used before it is initialized in constructor.

The analyzer detected a field (property) which is used before it is initialized in the class constructor.

Consider the following example:

    class Test
    {
      List<int> mylist;
      Test()
      {
        int count = mylist.Count;  // <=
        ....
        mylist = new List<int>();
      }
    }

In the constructor of the 'Test' class, property 'Count' of the list 'mylist' is accessed, while the list itself is initialized later. Executing this code fragment would lead to a null reference exception. To avoid it, the list must be initialized first, for example, at declaration:

    class Test
    {
      List<int> mylist = new List<int>();
      Test()
      {
        int count = mylist.Count;
        ....
      }
    }

Here is another example:

    class Test2
    {
      int myint;
      Test2(int param)
      {
        Foo(myint);  // <=
        ....
        myint = param;
      }
    }

In this code, field 'myint', whose default value is 0, is passed to the 'Foo' method. This could be done on purpose, and then there is no error. However, executing code like that can cause unexpected behavior in certain cases. A better solution is to explicitly initialize the 'myint' field, even to a default value of 0:

    class Test2
    {
      int myint = 0;
      Test2(int param)
      {
        Foo(myint);
        ....
        myint = param;
      }
    }

Now both the analyzer and other programmers can see that the code author took care of the 'myint' field and initialized it.

This diagnostic is classified as:

CWE-665

You can look at examples of errors detected by the V3128 diagnostic.