# Installing a binary distribution package

No official binary distribution packages are provided by the gflags developers.
There may, however, be binary packages available for your operating system.
Please consult also the package repositories of your Linux distribution.

On Debian/Ubuntu Linux, gflags can be installed using the following command:

    sudo apt-get install libgflags-dev

On macOS, [Homebrew](https://brew.sh/) includes a formula for gflags:

    brew install gflags


# Compiling the source code with Bazel

To use gflags in a [Bazel](http://bazel.io) project, map it in as an external
dependency by editing your WORKSPACE file:

    git_repository(
        name = "com_github_gflags_gflags",
        commit = "<INSERT COMMIT SHA HERE>",
        remote = "https://github.com/gflags/gflags.git",
    )

You can then add `@com_github_gflags_gflags//:gflags` to the `deps` section of a
`cc_binary` or `cc_library` rule, and `#include <gflags/gflags.h>` to include it
in your source code.


# Compiling the source code with vcpkg

You can download and install gflags using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:

    git clone https://github.com/Microsoft/vcpkg.git
    cd vcpkg
    ./bootstrap-vcpkg.sh
    ./vcpkg integrate install
    vcpkg install gflags

The gflags port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.


# Compiling the source code with CMake

The build system of gflags is since version 2.1 based on [CMake](http://cmake.org).
The common steps to build, test, and install software are therefore:

1. Extract source files.
2. Create build directory and change to it.
3. Run CMake to configure the build tree.
4. Build the software using selected build tool.
5. Test the built software.
6. Install the built files.

On Unix-like systems with GNU Make as build tool, these build steps can be
summarized by the following sequence of commands executed in a shell,
where ```$package``` and ```$version``` are shell variables which represent
the name of this package and the obtained version of the software.

    $ tar xzf gflags-$version-source.tar.gz
    $ cd gflags-$version
    $ mkdir build && cd build
    $ ccmake ..
    
      - Press 'c' to configure the build system and 'e' to ignore warnings.
      - Set CMAKE_INSTALL_PREFIX and other CMake variables and options.
      - Continue pressing 'c' until the option 'g' is available.
      - Then press 'g' to generate the configuration files for GNU Make.
    
    $ make
    $ make test    (optional)
    $ make install (optional)

In the following, only gflags-specific CMake settings available to
configure the build and installation are documented. Note that most of these
variables are for advanced users and binary package maintainers only.
They usually do not have to be modified.


CMake Option                | Description
--------------------------- | -------------------------------------------------------
CMAKE_INSTALL_PREFIX        | Installation directory, e.g., "/usr/local" on Unix and "C:\Program Files\gflags" on Windows.
BUILD_SHARED_LIBS           | Request build of dynamic link libraries.
BUILD_STATIC_LIBS           | Request build of static link libraries. Implied if BUILD_SHARED_LIBS is OFF.
BUILD_PACKAGING             | Enable binary package generation using CPack.
BUILD_TESTING               | Build tests for execution by CTest.
BUILD_NC_TESTS              | Request inclusion of negative compilation tests (requires Python).
BUILD_CONFIG_TESTS          | Request inclusion of package configuration tests (requires Python).
BUILD_gflags_LIBS           | Request build of multi-threaded gflags libraries (if threading library found).
BUILD_gflags_nothreads_LIBS | Request build of single-threaded gflags libraries.
GFLAGS_NAMESPACE            | Name of the C++ namespace to be used by the gflags library. Note that the public source header files are installed in a subdirectory named after this namespace. To maintain backwards compatibility with the Google Commandline Flags, set this variable to "google". The default is "gflags".
GFLAGS_INTTYPES_FORMAT      | String identifying format of built-in integer types.
GFLAGS_INCLUDE_DIR          | Name of headers installation directory relative to CMAKE_INSTALL_PREFIX.
LIBRARY_INSTALL_DIR         | Name of library installation directory relative to CMAKE_INSTALL_PREFIX.
INSTALL_HEADERS             | Request installation of public header files.
