Overview

This is protobuf-c, a C implementation of the Google Protocol Buffers data serialization format. It includes libprotobuf-c, a pure C library that implements protobuf encoding and decoding, and protoc-c, a code generator that converts Protocol Buffer .proto files to C descriptor code, based on the original protoc. protobuf-c formerly included an RPC implementation; that code has been split out into the protobuf-c-rpc project.

protobuf-c was originally written by Dave Benson and maintained by him through version 0.15 but is now being maintained by a new team. Thanks, Dave!

Mailing list

protobuf-c's mailing list is hosted on a Google Groups forum. Subscribe by sending an email to protobuf-c+subscribe@googlegroups.com.

Building

protobuf-c requires a C compiler, a C++ compiler, protobuf, and pkg-config to be installed.

./configure && make && make install

If building from a git checkout, the autotools (autoconf, automake, libtool) must also be installed, and the build system must be generated by running the autogen.sh script.

./autogen.sh && ./configure && make && make install

Test

If you want to execute test cases individually, please run the following command after running ./configure once:

 make check

Documentation

See the online Doxygen documentation here or the Wiki for a detailed reference. The Doxygen documentation can be built from the source tree by running:

make html

Synopsis

Use the protoc command to generate .pb-c.c and .pb-c.h output files from your .proto input file. The --c_out options instructs protoc to use the protobuf-c plugin.

protoc --c_out=. example.proto

Include the .pb-c.h file from your C source code.

#include "example.pb-c.h"

Compile your C source code together with the .pb-c.c file. Add the output of the following command to your compile flags.

pkg-config --cflags 'libprotobuf-c >= 1.0.0'

Link against the libprotobuf-c support library. Add the output of the following command to your link flags.

pkg-config --libs 'libprotobuf-c >= 1.0.0'

If using autotools, the PKG_CHECK_MODULES macro can be used to detect the presence of libprotobuf-c. Add the following line to your configure.ac file:

PKG_CHECK_MODULES([PROTOBUF_C], [libprotobuf-c >= 1.0.0])

This will place compiler flags in the PROTOBUF_C_CFLAGS variable and linker flags in the PROTOBUF_C_LDFLAGS variable. Read more information here about the PKG_CHECK_MODULES macro.

Versioning

protobuf-c follows the Semantic Versioning Specification as of version 1.0.0.

Note that as of version of 1.0.0, the header files generated by the protoc-c compiler contain version guards to prevent incompatibilities due to version skew between the .pb-c.h files generated by protoc-c and the public protobuf-c.h include file supplied by the libprotobuf-c support library. While we will try not to make changes to protobuf-c that will require triggering the version guard often, such as releasing a new major version of protobuf-c, this cannot be guaranteed. Thus, it's a good idea to recompile your .pb-c.c and .pb-c.h files from their source .proto files with protoc-c as part of your build system, with proper source file dependency tracking, rather than shipping potentially stale .pb-c.c and .pb-c.h files that may not be compatible with the libprotobuf-c headers installed on the system in project artifacts like repositories and release tarballs. (Note that the output of the protoc-c code generator is not standalone, as the output of some other tools that generate C code is, such as flex and bison.)

Major API/ABI changes may occur between major version releases, by definition. It is not recommended to export the symbols in the code generated by protoc-c in a stable library interface, as this will embed the protobuf-c ABI into your library's ABI. Nor is it recommended to install generated .pb-c.h files into a public header file include path as part of a library API, as this will tie clients of your library's API to particular versions of libprotobuf-c.

Contributing

Please send patches to the protobuf-c mailing list or by opening a GitHub pull request.

The most recently released protobuf-c version is kept on the master branch, while the next branch is used for commits targeted at the next release. Please base patches and pull requests against the next branch, not the master branch.

Copyright to all contributions are retained by the original author, but must be licensed under the terms of the BSD-2-Clause license. Please add a Signed-off-by header to your commit message (git commit -s) to indicate that you are licensing your contribution under these terms.