# Fwd: out-of-tree module config.h documentation/use **URL:** \ **Category:** GNU Radio\ **Created:** [October 24, 2014, 11:21am UTC](https://www.ruby-forum.com/t/fwd-out-of-tree-module-config-h-documentation-use/232729 "2014-10-24T11:21:18Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [October 24, 2014, 11:21am UTC](https://www.ruby-forum.com/t/fwd-out-of-tree-module-config-h-documentation-use/232729/1 "2014-10-24T11:21:18Z")
Hi I am writing an out-of-tree module and have used the gr\_modtool to generate the module and block skeletons. All the block source files include a config.h file, but I have not been able to find documentation of its use or location anywhere. Does anyone know what it is used for and how? Thank you, David Marmoy ---
**Author:** ![David\_Marmoy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58956e/32.png) [@David\_Marmoy](https://www.ruby-forum.com/u/David_Marmoy)\ **Post date:** [October 24, 2014, 12:10pm UTC](https://www.ruby-forum.com/t/fwd-out-of-tree-module-config-h-documentation-use/232729/2 "2014-10-24T12:10:05Z")
It’s probably an artefact from the autotools era. Note that it’s: 21 #ifdef HAVE\_CONFIG\_H 22 #include “config.h” 23 #endif So the include is never called. These config.h files are usually generated by the build process, and provide information about the system you’re building on. CMake handles that a bit differently, so we don’t really use these anymore. We could of course generate such a file with CMake, but we currently don’t. Cheers, M