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Installing C++ Distributions of PyTorch
=======================================
We provide binary distributions of all headers, libraries and CMake
configuration files required to depend on PyTorch. We call this distribution
*LibTorch*, and you can download ZIP archives containing the latest LibTorch
distribution on `our website <https://pytorch.org/get-started/locally/>`_. Below
is a small example of writing a minimal application that depends on LibTorch
and uses the ``torch::Tensor`` class which comes with the PyTorch C++ API.
Minimal Example
---------------
The first step is to download the LibTorch ZIP archive via the link above. For
example:
.. code-block:: sh
wget https://download.pytorch.org/libtorch/nightly/cpu/libtorch-shared-with-deps-latest.zip
unzip libtorch-shared-with-deps-latest.zip
Note that the above link has CPU-only libtorch. If you would like to download a GPU-enabled
libtorch, find the right link in the link selector on https://pytorch.org
If you're a Windows developer and wouldn't like to use CMake, you could jump to the Visual Studio
Extension section.
Next, we can write a minimal CMake build configuration to develop a small
application that depends on LibTorch. CMake is not a hard requirement for using
LibTorch, but it is the recommended and blessed build system and will be well
supported into the future. A most basic `CMakeLists.txt` file could look like
this:
.. code-block:: cmake
cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
project(example-app)
find_package(Torch REQUIRED)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TORCH_CXX_FLAGS}")
add_executable(example-app example-app.cpp)
target_link_libraries(example-app "${TORCH_LIBRARIES}")
set_property(TARGET example-app PROPERTY CXX_STANDARD 14)
# The following code block is suggested to be used on Windows.
# According to https://github.com/pytorch/pytorch/issues/25457,
# the DLLs need to be copied to avoid memory errors.
if (MSVC)
file(GLOB TORCH_DLLS "${TORCH_INSTALL_PREFIX}/lib/*.dll")
add_custom_command(TARGET example-app
POST_BUILD
COMMAND ${CMAKE_COMMAND} -E copy_if_different
${TORCH_DLLS}
$<TARGET_FILE_DIR:example-app>)
endif (MSVC)
The implementation of our example will simply create a new `torch::Tensor` and
print it:
.. code-block:: cpp
#include <torch/torch.h>
#include <iostream>
int main() {
torch::Tensor tensor = torch::rand({2, 3});
std::cout << tensor << std::endl;
}
While there are more fine-grained headers you can include to access only parts
of the PyTorch C++ API, including `torch/torch.h` is the most sure-proof way of
including most of its functionality.
The last step is to build the application. For this, assume our example
directory is laid out like this:
.. code-block:: sh
example-app/
CMakeLists.txt
example-app.cpp
We can now run the following commands to build the application from within the
``example-app/`` folder:
.. code-block:: sh
mkdir build
cd build
cmake -DCMAKE_PREFIX_PATH=/absolute/path/to/libtorch ..
cmake --build . --config Release
where ``/absolute/path/to/libtorch`` should be the absolute (!) path to the unzipped LibTorch
distribution. If PyTorch was installed via conda or pip, `CMAKE_PREFIX_PATH` can be queried
using `torch.utils.cmake_prefix_path` variable. In that case CMake configuration step would look something like follows:
.. code-block:: sh
cmake -DCMAKE_PREFIX_PATH=`python -c 'import torch;print(torch.utils.cmake_prefix_path)'`
If all goes well, it will look something like this:
.. code-block:: sh
root@4b5a67132e81:/example-app# mkdir build
root@4b5a67132e81:/example-app# cd build
root@4b5a67132e81:/example-app/build# cmake -DCMAKE_PREFIX_PATH=/path/to/libtorch ..
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - not found
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE
-- Configuring done
-- Generating done
-- Build files have been written to: /example-app/build
root@4b5a67132e81:/example-app/build# cmake --build . --config Release
Scanning dependencies of target example-app
[ 50%] Building CXX object CMakeFiles/example-app.dir/example-app.cpp.o
[100%] Linking CXX executable example-app
[100%] Built target example-app
Executing the resulting ``example-app`` binary found in the ``build`` folder
should now merrily print the tensor (exact output subject to randomness):
.. code-block:: sh
root@4b5a67132e81:/example-app/build# ./example-app
0.2063 0.6593 0.0866
0.0796 0.5841 0.1569
[ Variable[CPUFloatType]{2,3} ]
.. tip::
On Windows, debug and release builds are not ABI-compatible. If you plan to
build your project in debug mode, please try the debug version of LibTorch.
Also, make sure you specify the correct configuration in the ``cmake --build .``
line above.
Visual Studio Extension
-----------------------
`LibTorch Project Template <https://marketplace.visualstudio.com/items?itemName=YiZhang.LibTorch001>`_ can help Windows developers
set all libtorch project settings and link options for debug and release.
It's easy to use and you could check out the `demo video <https://ossci-windows.s3.us-east-1.amazonaws.com/vsextension/demo.mp4>`_.
The only prerequisite is to download the libtorch on https://pytorch.org
Support
-------
If you run into any troubles with this installation and minimal usage guide,
please use our `forum <https://discuss.pytorch.org/>`_ or `GitHub issues
<https://github.com/pytorch/pytorch/issues>`_ to get in touch.
|
