C＃获取char *类型的实例

Question

is it possible to get an instance of an pointer during runtime? Something like:

Type x = typeof(char*);

How do I get a instance of this pointer? The problem is that I only have a Object with an Type inside. And I know that the Type is a pointer. But now I need a instance of the pointer.

Answer 1

You can:

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

and back:

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

But perhaps what you want is something different:

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));
    }
}

See how for the TestPointer , ignoring some problems with non-blittable types, I simply use GCHandle to obtain a pointer to the value and then pass it directly to the method. No unsafe code necessary :-)

For TestReference it is much easier: I only need to create the parameters array separately, and then the CLR will put in that array the modified values.