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HOWTO: using the Cloud Document AI API C++ client in your project

This directory contains small examples showing how to use the Cloud Document AI API C++ client library in your own project. These instructions assume that you have some experience as a C++ developer and that you have a working C++ toolchain (compiler, linker, etc.) installed on your platform.

  • Packaging maintainers or developers who prefer to install the library in a fixed directory (such as /usr/local or /opt) should consult the packaging guide.
  • Developers wanting to use the libraries as part of a larger CMake or Bazel project should consult the current document. Note that there are similar documents for each library in their corresponding directories.
  • Developers wanting to compile the library just to run some examples or tests should consult the building and installing section of the top-level README file.
  • Contributors and developers to google-cloud-cpp should consult the guide to set up a development workstation.

Before you begin

To run the quickstart examples you will need a working Google Cloud Platform (GCP) project. The quickstart covers the necessary steps in detail.

Configuring authentication for the C++ Client Library

Like most Google Cloud Platform (GCP) services, Cloud Document AI API requires that your application authenticates with the service before accessing any data. If you are not familiar with GCP authentication please take this opportunity to review the Authentication Overview. This library uses the GOOGLE_APPLICATION_CREDENTIALS environment variable to find the credentials file. For example:

Shell Command
Bash/zsh/ksh/etc. export GOOGLE_APPLICATION_CREDENTIALS=[PATH]
sh GOOGLE_APPLICATION_CREDENTIALS=[PATH];
export GOOGLE_APPLICATION_CREDENTIALS
csh/tsch setenv GOOGLE_APPLICATION_CREDENTIALS [PATH]
Windows Powershell $env:GOOGLE_APPLICATION_CREDENTIALS=[PATH]
Windows cmd.exe set GOOGLE_APPLICATION_CREDENTIALS=[PATH]

Setting this environment variable is the recommended way to configure the authentication preferences, though if the environment variable is not set, the library searches for a credentials file in the same location as the Cloud SDK. For more information about Application Default Credentials, see https://cloud.google.com/docs/authentication/production

Using with Bazel

⚠️ If you are using Windows or macOS there are additional instructions at the end of this document.

  1. Install Bazel using the instructions from the bazel.build website.

  2. Compile this example using Bazel:

    cd $HOME/google-cloud-cpp/google/cloud/documentai/quickstart
bazel build ...

    Note that Bazel automatically downloads and compiles all dependencies of the project. As it is often the case with C++ libraries, compiling these dependencies may take several minutes.

  3. Run the example, changing the placeholder(s) to appropriate values:

    bazel run :quickstart -- [PROJECT_ID] [LOCATION_ID] [PROCESSOR_ID]

Using with CMake

⚠️ If you are using Windows or macOS there are additional instructions at the end of this document.

  1. Install CMake. The package managers for most Linux distributions include a package for CMake. Likewise, you can install CMake on Windows using a package manager such as chocolatey, and on macOS using homebrew. You can also obtain the software directly from the cmake.org.

  2. Install the dependencies with your favorite tools. As an example, if you use vcpkg:

    cd $HOME/vcpkg
./vcpkg install google-cloud-cpp[core,documentai]

    Note that, as it is often the case with C++ libraries, compiling these dependencies may take several minutes.

  3. Configure CMake, if necessary, configure the directory where you installed the dependencies:

    cd $HOME/gooogle-cloud-cpp/google/cloud/documentai/quickstart
cmake -H. -B.build -DCMAKE_TOOLCHAIN_FILE=$HOME/vcpkg/scripts/buildsystems/vcpkg.cmake
cmake --build .build

  4. Run the example, changing the placeholder(s) to appropriate values:

    .build/quickstart [PROJECT_ID] [LOCATION_ID] [PROCESSOR_ID]

Platform Specific Notes

macOS

gRPC requires an environment variable to configure the trust store for SSL certificates, you can download and configure this using:

curl -Lo roots.pem https://pki.google.com/roots.pem
export GRPC_DEFAULT_SSL_ROOTS_FILE_PATH="$PWD/roots.pem"

To workaround a bug in Bazel, gRPC requires this flag on macOS builds, you can add the option manually or include it in your .bazelrc file:

bazel build --copt=-DGRPC_BAZEL_BUILD ...

Windows

Bazel tends to create very long file names and paths. You may need to use a short directory to store the build output, such as c:\b, and instruct Bazel to use it via:

bazel --output_user_root=c:\b build ...

gRPC requires an environment variable to configure the trust store for SSL certificates, you can download and configure this using:

@powershell -NoProfile -ExecutionPolicy unrestricted -Command ^
    (new-object System.Net.WebClient).Downloadfile( ^
        'https://pki.google.com/roots.pem', 'roots.pem')
set GRPC_DEFAULT_SSL_ROOTS_FILE_PATH=%cd%\roots.pem