pw_flatbuffers#

Experimental

The flatbuffers module supports the use of cmake to build C++ headers from a set of flatbuffers schema files. The user of these build files may either use the provided flatbuffers distribution or provide their own.

Flatbuffers compilation#

pw_flatbuffers currently only supports cmake as the build system.

CMake#

CMake provides a pw_flatbuffer_library function to build flatbuffer schema files into C++ headers. The user of this function is expected to configure the flatbuffers compiler as well as provide any needed dependencies such as flatbuffers headers. Support for outputting other languages supported by flatc is currently not implemented.

Arguments

  • NAME: Name of dependency to create. The dependency target name will be NAME.cpp

  • SOURCES: Source schema files to compile to headers.

  • DEPS: Dependencies needed to compile the passed in schema files

  • PREFIX: Prefix path to be appended to the generated header path.

  • STRIP_PREFIX: Prefix to be removed from the generated header path. This is applied before PREFIX.

  • FLATC_FLAGS: flags to be passed to flatc when building

Note here that by default, the generated header path will be the relative path between the CMakeLists.txt containing the build rule and the schema it compiles. The name of the include file will be the name of the schema file, suffixed with _generated.h. For example, if a CMakeLists.txt at the toplevel includes a schema foo/schema.fbs, then the compiled header would be included as #include "foo/schema_generated.h".

Globals

Additionally, several global cache variables influence the behavior of pw_flatbuffer_library.

  • pw_flatbuffers_FLATC: Path to the flatbuffers compiler executable. This defaults to simply using flatc and relying on the shell PATH to locate the compiler.

  • pw_flatbuffers_FLATC_FLAGS: Global flags to pass to all invocations of the flatc compiler. Defaults to empty.

  • pw_flatbuffers_LIBRARY: Flatbuffer header library dependency to automatically add to all flatbuffers libraries built. Defaults to unset unless using the pigweed provided flatbuffers by setting dir_pw_third_party_flatbuffers, in which case this will default to the pigweed provided third party flatbuffers. If left unset, the user takes responsibility for properly providing the flatbuffer dependencies to code.

Example

# Point to our installed directory
set(dir_pw_third_party_flatbuffers ${path_to_flatbuffers_install})

# Set global flags, such as the C++ version
set(pw_flatbuffers_FLATC_FLAGS --cpp-std c++11 CACHE LIST "Global args to flatc")

include($ENV{PW_ROOT}/pw_build/pigweed.cmake)
include($ENV{PW_ROOT}/pw_flatbuffers/flatbuffers.cmake)

# Build the fbs files to headers
pw_flatbuffer_library(simple_test_schema
  SOURCES
    pw_flatbuffers_test_schema/simple_test.fbs
)

# Build a test exe
pw_add_test(pw_flatbuffers.simple_test
  SOURCES
    simple_test.cc
  PRIVATE_DEPS
    simple_test_schema.cpp
  GROUPS
    modules
)

GN#

GN is not currently supported.

Bazel#

Bazel is not currently supported.

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