Question

在下面的代码中引发了异常。

'type无法整理，因为嵌入式数组的长度实例与布局中声明的长度不匹配

我知道是因为字符串和char数组的长度不匹配，所以我试图用空白字符固定字符串的长度。

要添加空白字符，我应该知道RUNTIME中目标char数组的长度，但我不能知道，因为char数组成员还为null。

如何获取char数组的长度？有没有比我更好的方法了？

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct TestStruct
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)] public char[] CharArray;
}

private void Button1_Click(object sender, RoutedEventArgs e)
{
    var _TestStruct = new TestStruct();
    var _IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(_TestStruct));
    var _String = "a";

    _TestStruct.CharArray = _String.ToCharArray();
    Marshal.StructureToPtr(_TestStruct, _IntPtr, false); // ERROR

    // void TestFunction(IntPtr _Intptr);
    Marshal.FreeHGlobal(_IntPtr);
}

Answer 1

如果将5定义为常量，则可以将char数组填充为零，以使其填充所需的大小：

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct TestStruct
{
    public const int CharArraySize = 5;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = CharArraySize)] public char[] CharArray;
}

private void Button1_Click(object sender, RoutedEventArgs e)
{
    TestStruct _TestStruct = new TestStruct();

    IntPtr _IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(_TestStruct));

    string _String = "a";

    _TestStruct.CharArray = _String.ToCharArray();
    if (_TestStruct.CharArray.Length < TestStruct.CharArraySize)
        _TestStruct.CharArray = _TestStruct.CharArray.Concat(Enumerable.Repeat((char)0, TestStruct.CharArraySize - _TestStruct.CharArray.Length)).ToArray();

    Marshal.StructureToPtr(_TestStruct, _IntPtr, false); // This works now

    // void TestFunction(IntPtr _Intptr);

    Marshal.FreeHGlobal(_IntPtr);
}

您可以使用反射使此过程自动化：

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct TestStruct
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)] public char[] CharArray;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)] public char[] CharArray2;
}

private void Button1_Click(object sender, RoutedEventArgs e)
{
    TestStruct _TestStruct = new TestStruct();

    IntPtr _IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(_TestStruct));

    _TestStruct.CharArray = "abcd".ToCharArray();
    _TestStruct.CharArray2 = "ab".ToCharArray();
    _TestStruct = (TestStruct)FixArraySizes(_TestStruct); // Due to TestStruct being a struct, we must unbox the result.

    Marshal.StructureToPtr(_TestStruct, _IntPtr, false);

    // void TestFunction(IntPtr _Intptr);

    Marshal.FreeHGlobal(_IntPtr);
}

private object FixArraySizes(object obj) {
    var objType = obj.GetType();
    var fieldInfos = objType.FindMembers(MemberTypes.Field, BindingFlags.Public | BindingFlags.Instance, (info, _) => ((FieldInfo)info).FieldType == typeof(char[]), null);
    foreach (FieldInfo info in fieldInfos) {
        var fieldValue = (char[])info.GetValue(obj);
        var sizeOfArray = (int?)info.GetCustomAttributesData().FirstOrDefault(attr => attr.AttributeType == typeof(MarshalAsAttribute))?.NamedArguments.FirstOrDefault(arg => arg.MemberName == "SizeConst").TypedValue.Value;
        if (sizeOfArray.HasValue)
        {
            fieldValue = FixArraySize(fieldValue, sizeOfArray.Value);
            info.SetValue(obj, fieldValue);
        }
    }

    return obj;
}

private char[] FixArraySize(char[] array, int expectedSize)
{
    if (array.Length < expectedSize)
        array = array.Concat(Enumerable.Repeat((char)0, expectedSize - array.Length)).ToArray();
    return array;
}

如何在运行时知道属于结构的char数组的长度

1 个答案: