'torch/torch.h' file not found in header file

I'm new in Linux C++ programming. I have to use libtorch (pytorch C++ version), but I kept struggling with C++ and cmake problems. These problems really make me mad, and I need some help.

Here is a simple C++ project:

.
├── build.sh
├── CMakeLists.txt
├── load_data
│   ├── CMakeLists.txt
│   ├── include
│   │   └── load_data
│   │       └── load_data.hpp
│   └── src
│       └── load_data.cpp
└── src
    └── main.cpp

But I can't build it because load_data/include/load_data/load_data.hpp cannot #include <torch/torch.h>.

The build error message:

[build] /my/path/load_data/include/load_data/load_data.hpp:4:10: fatal error: 'torch/torch.h' file not found
[build] #include <torch/torch.h>
[build]          ^~~~~~~~~~~~~~~

However, if I move the #include <torch/torch.h> from the header file to the corresponding source file, the error message goes away. It makes me confused.

Files' contents:

• load_data/include/load_data/load_data.hpp

  #pragma once
  
  #include <torch/torch.h>
  
  namespace load_data
  {
      void try_torch();
      // torch::Tensor rand_tensor();
  }
  

• load_data/src/load_data.cpp

  # include "load_data/load_data.hpp"
  
  // If I remove it from load_data.hpp and use it here, the error goes away.
  // #include <torch/torch.h>
  
  namespace load_data {
      void try_torch(){
          torch::Tensor tensor = torch::rand({2, 3});
          std::cout << tensor << std::endl;
      }
  }
  

• src/main.cpp

  #include <string>
  
  #include "load_data/load_data.hpp"
  
  int main(int argc, char **argv)
  {
      load_data::try_torch();
      return 0;
  }
  

• CMakeLists.txt

  cmake_minimum_required (VERSION 3.21)
  
  set(CMAKE_CXX_COMPILER clang++-13)
  
  project(ldt-cpp-experiments VERSION 1.0.0 LANGUAGES CXX)
  
  
  find_package(Torch REQUIRED)
  message(STATUS "Torch_FOUND: ${Torch_FOUND}")
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TORCH_CXX_FLAGS}")
  
  add_subdirectory("load_data")
  
  
  set(EXECUTABLE_NAME main)
  
  add_executable(${EXECUTABLE_NAME} src/main.cpp)
  
  
  target_link_libraries(${EXECUTABLE_NAME}
      PRIVATE load_data
  )
  
  set_target_properties(${EXECUTABLE_NAME} PROPERTIES
    CXX_STANDARD 20
    CXX_STANDARD_REQUIRED YES
  )
  
  

• load_data/CMakeLists.txt

  cmake_minimum_required(VERSION 3.21)
  
  project (load_data VERSION 1.0.0 LANGUAGES CXX)
  
  
  find_package(Torch REQUIRED)
  message(STATUS "Torch_FOUND: ${Torch_FOUND}")
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TORCH_CXX_FLAGS}")
  
  
  set(LIB_NAME "load_data")
  
  add_library(${LIB_NAME}
      SHARED 
  )
  
  target_sources(${LIB_NAME}
      PRIVATE
          ${PROJECT_SOURCE_DIR}/src/load_data.cpp
  )
  
  target_sources(${LIB_NAME}
      PRIVATE
          ${PROJECT_SOURCE_DIR}/src/load_data.cpp
          ${PROJECT_SOURCE_DIR}/include/load_data/load_data.hpp
  )
  
  target_include_directories(${LIB_NAME}
      PUBLIC 
          ${PROJECT_SOURCE_DIR}/include
  )
  
  target_link_libraries(${LIB_NAME}
      PRIVATE
          ${TORCH_LIBRARIES}
  )
  
  set_target_properties(${LIB_NAME} PROPERTIES
    CXX_STANDARD 20
    CXX_STANDARD_REQUIRED YES
  )
  
  

• build.sh

  cmake -S . -B build