C# 获取 char* 类型的实例

Question

是否可以在运行时获取指针的实例？ 比如：

Type x = typeof(char*);

如何获取此指针的实例？问题是我只有一个里面有一个类型的对象。而且我知道 Type 是一个指针。但现在我需要一个指针的实例。

Answer 1

你可以：

Type typeChar = typeof(char);
Type ptrChar = typeChar.MakePointerType(); // char*

然后返回：

if (ptrChar.IsPointer)
{
    Type typeChar2 = ptrChar.GetElementType(); // char
}

但也许你想要的是不同的东西：

public class TestBool
{
    unsafe public void Test(bool* pointer)
    {
        *pointer = true;
    }

    public void Test2(ref bool reference)
    {
        reference = true;
    }
}

public class TestChar
{
    unsafe public void Test(char* pointer)
    {
        *pointer = 'A';
    }

    public void Test2(ref char reference)
    {
        reference = 'B';
    }
}

public static void TestPointer(object obj, Type parType)
{
    var pointerMethod = obj.GetType().GetMethod("Test");

    Type parType2;

    // Non-blittable types aren't directly supported. 
    // See https://msdn.microsoft.com/en-us/library/75dwhxf7.aspx
    // We cheat a little.
    if (parType == typeof(bool))
    {
        parType2 = typeof(byte);
    }
    else if (parType == typeof(char))
    {
        parType2 = typeof(short);
    }
    else if (parType.IsEnum)
    {
        parType2 = Enum.GetUnderlyingType(parType);
    }
    else
    {
        parType2 = parType;
    }

    object obj2 = Activator.CreateInstance(parType2);
    GCHandle handle = default(GCHandle);

    try
    {
        handle = GCHandle.Alloc(obj2, GCHandleType.Pinned);

        pointerMethod.Invoke(obj, new object[] { handle.AddrOfPinnedObject() });
    }
    finally
    {
        if (handle.IsAllocated)
        {
            handle.Free();
        }
    }

    if (parType == typeof(bool))
    {
        obj2 = (byte)obj2 != 0;
    }
    else if (parType == typeof(char))
    {
        obj2 = (char)(short)obj2;
    }
    else if (parType.IsEnum)
    {
        obj2 = Enum.ToObject(parType, obj2);
    }

    Console.WriteLine(obj2);
}

public static void TestReference(object obj, Type parType)
{
    var referenceMethod = obj.GetType().GetMethod("Test2");

    object obj2 = Activator.CreateInstance(parType);
    var pars = new object[] { obj2 };

    referenceMethod.Invoke(obj, pars);

    Console.WriteLine(pars[0]);
}

private static void Main(string[] args)
{
    {
        var obj = new TestBool();
        TestPointer(obj, typeof(bool));
        TestReference(obj, typeof(bool));
    }

    {
        var obj = new TestChar();
        TestPointer(obj, typeof(char));
        TestReference(obj, typeof(char));
    }
}

看看TestPointer 是如何处理的，忽略一些非blittable 类型的问题，我只是简单地使用GCHandle 来获取指向值的指针，然后将它直接传递给方法。不需要不安全的代码:-)

TestReference 就简单多了：我只需要单独创建参数数组，然后 CLR 会将修改后的值放入该数组中。