-
Notifications
You must be signed in to change notification settings - Fork 5.5k
Problem marshalling with Unmanaged.LPUTF8Str #52810
-
I didn't want to file this as a bug because I think I'm causing the problem but I don't know why.
I'm updating our Vulkan library P/Invokes and interop structures to .NET5 where we can use the Unmanaged.LPUTF8Str for marshalling UTF8 (nul-terminated) strings. So decided to go with this instead of marshalling as byte and then converting it to a C# string which makes our code more readable.
The problem is though, that the method
[DllImport(VulkanLibrary.Name)] static extern void vkGetPhysicalDeviceProperties(IntPtr physicalDevice, out VkPhysicalDeviceProperties properties);
throws some memory exception with the struct given below. The docs explicitly say that it is a nul-terminated UTF8 string so I thought it should work. What does work is using UnmanagedType.ByValTStr and I have no clue why.
[StructLayout(LayoutKind.Sequential)] public readonly struct VkPhysicalDeviceProperties { public readonly VulkanVersion ApiVersion; public readonly VulkanVersion DriverVersion; public readonly int VendorId; public readonly int DeviceId; public readonly VkPhysicalDeviceType DeviceType; // The docs say that it is an UTF8 (nul-terminated) string, the question is why LPUTF8Str doesn't work. [MarshalAs(UnmanagedType.ByValTStr, SizeConst = MaxPhysicalDeviceNameSize)] public readonly string DeviceName; public readonly Guid PipelineCacheUuid; public readonly VkPhysicalDeviceLimits Limits; public readonly VkPhysicalDeviceSparseProperties SparseProperties; }
Beta Was this translation helpful? Give feedback.
All reactions
The difference between ByValTStr and LPUTF8Str is where the string is placed in memory.
For the ByValTStr case, the native representation of the VkPhysicalDeviceProperties struct would look like the following:
struct VkPhysicalDeviceProperties { VulkanVersion ApiVersion; VulkanVersion DriverVersion; int VendorId; int DeviceId; VkPhysicalDeviceType DeviceType; char DeviceName[MaxPhysicalDeviceNameSize]; // Marshalled in-place in the structure GUID PipelineCacheUuid; VkPhysicalDeviceLimits Limits; VkPhysicalDeviceSparseProperties SparseProperties; };
For the LPUTF8Str case, the string is marshalled as a poin...
Replies: 1 comment 2 replies
-
The difference between ByValTStr and LPUTF8Str is where the string is placed in memory.
For the ByValTStr case, the native representation of the VkPhysicalDeviceProperties struct would look like the following:
struct VkPhysicalDeviceProperties { VulkanVersion ApiVersion; VulkanVersion DriverVersion; int VendorId; int DeviceId; VkPhysicalDeviceType DeviceType; char DeviceName[MaxPhysicalDeviceNameSize]; // Marshalled in-place in the structure GUID PipelineCacheUuid; VkPhysicalDeviceLimits Limits; VkPhysicalDeviceSparseProperties SparseProperties; };
For the LPUTF8Str case, the string is marshalled as a pointer to the allocated string, so the struct would look like the following:
struct VkPhysicalDeviceProperties { VulkanVersion ApiVersion; VulkanVersion DriverVersion; int VendorId; int DeviceId; VkPhysicalDeviceType DeviceType; char* DeviceName; // Marshalled as a pointer GUID PipelineCacheUuid; VkPhysicalDeviceLimits Limits; VkPhysicalDeviceSparseProperties SparseProperties; };
From what it sounds like, the ByValTStr case has the matching layout to the native code, which would be why it works and why the LPUTF8Str case does not.
Beta Was this translation helpful? Give feedback.
All reactions
-
@jkoritzinsky: Thanks a lot for explaining this. For me it was not obvious from the docs.
Beta Was this translation helpful? Give feedback.
All reactions
-
@jkoritzinsky: Bardzo dziękuję za wyjaśnienie. Dla mnie nie było to oczywiste w dokumentacji.
Beta Was this translation helpful? Give feedback.