Incompatible std::string

windows
1

I’m using MSVS 2022, UE 5.3.2, and libtorch - debug-2.2.2+cu121.
I created a simple UE FPS project, added a code into a GameMode class, that loads libtorch.
Added a code like:

torch::jit::script::Module module_pt;
module_pt = torch::jit::load(“C:/src/model_weights.pt”);

This code compiled, linked, and I started the UEditor from MSVS. The UEditor has crashed on torch::jit::load with a runtime exception, going deep into the C runtime

ucrtbased.dll!00007ffb27daa053() Unknown No symbols loaded.
ucrtbased.dll!00007ffb27daa627() Unknown No symbols loaded.
msvcp140d.dll!00007ffb27f46c12() Unknown No symbols loaded.
msvcp140d.dll!00007ffb27f469e4() Unknown No symbols loaded.
msvcp140d.dll!00007ffb27f46b75() Unknown No symbols loaded.
torch_cpu.dll!std::basic_filebuf<char,std::char_traits>::open(const char * _Filename, int _Mode, int _Prot) Line 277 C++ Symbols loaded.
torch_cpu.dll!std::basic_ifstream<char,std::char_traits>::basic_ifstream<char,std::char_traits>(const char * _Filename, int _Mode, int _Prot) Line 808 C++ Symbols loaded.
torch_cpu.dll!std::basic_ifstream<char,std::char_traits>::basic_ifstream<char,std::char_traits>(const std::string & _Str, int _Mode, int _Prot) Line 815 C++ Symbols loaded.
torch_cpu.dll!torch::jit::getFileFormat(const std::string & filename) Line 113 C++ Symbols loaded.
torch_cpu.dll!torch::jit::import_ir_module(std::shared_ptrtorch::jit::CompilationUnit cu, const std::string & filename, std::optionalc10::Device device, std::unordered_map<std::string,std::string,std::hashstd::string,std::equal_tostd::string,std::allocator<std::pair<std::string const ,std::string>>> & extra_files, bool load_debug_files, bool restore_shapes) Line 429 C++ Symbols loaded.
torch_cpu.dll!torch::jit::import_ir_module(std::shared_ptrtorch::jit::CompilationUnit cu, const std::string & filename, std::optionalc10::Device device, bool load_debug_files) Line 416 C++ Symbols loaded.
> torch_cpu.dll!torch::jit::load(const std::string & filename, std::optionalc10::Device device, bool load_debug_files) Line 498 C++ Symbols loaded.
UnrealEditor-RASample.dll!ARASampleGameMode::InitPytorch() Line 84 C++ Symbols loaded.
UnrealEditor-RASample.dll!ARASampleGameMode::ARASampleGameMode() Line 48 C++ Symbols loaded.

After debugging I figured out that the torch::jit::load is not receiving the string value, that I’ve passed, but receives NULL.
My C string value is converted to std::string on my side, but inside torch::jit::load it crosses dll boundary, and gets converted to NULL, probably because of different versions of std::string being used on my machine and machine used to build the libtorch distribution.

What could be done in this case?
Build libtorch locally from sources?

2

I haven’t seen this issue before, but since you are concerned about the std::string definition, you might want to check if your installed libtorch version is using the cxx11 ABI or not and swap it for testing purposes.

3

Thank you for reply.
How can I do the check that you suggested?
BTW, using dumpbin I was able to get linker version used to buid the libtorch, which is 14.29

4

Oh sorry, I see there is no cxx11 ABI - specific build for Windows and I’m also unsure how it’s handled in these builds, as I’m using linux mostly.

5

I’ve followed steps from this article Integrate Libtorch into Unreal Engine 4: _ivalue_INTERNAL ASSERT FAILED · Issue #69425 · pytorch/pytorch · GitHub. Created dll project in MSVS, moved call of the module.forward() into the dll. That project produces .lib and .dll that I use in my UE5 project as described.

Now, call to module.forward() produces exception:
UnrealEditor.exe: Microsoft C++ exception: c10::Error at memory location 0x000000F7AE178AB0
This looks like the same issue, as in that article. Not fixed for years…

Name Value Type
:arrow_forward: what_without_backtrace_ "ivalue INTERNAL ASSERT FAILED at "C:\\actions-runner\\_work\\pytorch\\pytorch\\builder\\windows\\pytorch\\torch/csrc/jit/api/object.h":38, please report a bug to PyTorch. " std::string
6

Ok, that article has an error, found it, fixed my issue with c10 error.
The libtorch returns values for the input to a nn from simple .pt file prepared from py code. Yu-hOOO

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