Skip to content


Repository files navigation

c-ares logo

Build Status Windows Build Status Coverage Status CII Best Practices Fuzzing Status Bugs Coverity Scan Status

This is c-ares, an asynchronous resolver library. It is intended for applications which need to perform DNS queries without blocking, or need to perform multiple DNS queries in parallel. The primary examples of such applications are servers which communicate with multiple clients and programs with graphical user interfaces.

The full source code is available in the 'c-ares' release archives, and in a git repository: See the file for build information.

If you find bugs, correct flaws, have questions or have comments in general in regard to c-ares (or by all means the original ares too), get in touch with us on the c-ares mailing list:

c-ares is distributed under the MIT license.

You'll find all c-ares details and news here:

Notes for c-ares hackers

  • The distributed ares_build.h file is only intended to be used on systems which can not run the also distributed configure script.

  • The distributed ares_build.h file is generated as a copy of ares_build.h.dist when the c-ares source code distribution archive file is originally created.

  • If you check out from git on a non-configure platform, you must run the appropriate buildconf* script to set up ares_build.h and other local files before being able to compile the library.

  • On systems capable of running the configure script, the configure process will overwrite the distributed ares_build.h file with one that is suitable and specific to the library being configured and built, this new file is generated from the template file.

  • If you intend to distribute an already compiled c-ares library you MUST also distribute along with it the generated ares_build.h which has been used to compile it. Otherwise, the library will be of no use for the users of the library that you have built. It is your responsibility to provide this file. No one at the c-ares project can know how you have built the library.

  • File ares_build.h includes platform and configuration dependent info, and must not be modified by anyone. Configure script generates it for you.

  • We cannot assume anything else but very basic compiler features being present. While c-ares requires an ANSI C compiler to build, some of the earlier ANSI compilers clearly can't deal with some preprocessor operators.

  • Newlines must remain unix-style for older compilers' sake.

  • Comments must be written in the old-style /* unnested C-fashion */

  • Try to keep line lengths below 80 columns.