Compiler Error CS0269

使用了未赋值的 out 参数“parameter”

编译器未能验证在使用 out 参数之前是否已给它赋值,它的值在赋值时可能未定义。在访问值之前,请确保为调用的方法中的 out 参数赋值。如果您需要使用传入的变量的值,请改用 ref 参数。有关更多信息,请参见传递参数(C# 编程指南)

下面的示例生成 CS0269:

// CS0269.cs
class C
{
    public static void F(out int i)
    // One way to resolve the error is to use a ref parameter instead
    // of an out parameter.
    //public static void F(ref int i)
    {
        // The following line causes a compiler error because no value
        // has been assigned to i.
        int k = i;  // CS0269
        i = 1;
        // The error does not occur if the order of the two previous 
        // lines is reversed.
    }

    public static void Main()
    {
        int myInt = 1;
        F(out myInt);
        // If the declaration of method F is changed to require a ref
        // parameter, ref must be specified in the call as well.
        //F(ref myInt);
    }
}

如果变量的初始化发生在 try 块中,则也会出现此错误,因为编译器无法验证 try 块是否可以成功执行:

// CS0269b.cs
class C
{
    public static void F(out int i)
    {
        try
        {
            // Assignment occurs, but compiler can't verify it
            i = 1;
        }
        catch
        {
        }

        int k = i;  // CS0269
        i = 1;
    }

    public static void Main()
    {
        int myInt;
        F(out myInt);
    }
}