Reasons to hate C/C++ work previous: Reviewing Lightning memory-mapped database library: On page splits and other painful things next: Reviewing Lightning memory-mapped database library: A thoughtful hiatus The following code won’t link. For fun, the set_mapsize and set_flags are both defined in the same file. Both for .h & .c, and the set_mapsize works just fine. Comments 08/04/2013 01:01 PM by tobi I never understood why the header-based link system is needed. .NET and Java don't need them either, and they work much better. 08/04/2013 01:22 PM by Ayende Rahien tobi, They are needed because this way, you could write a single pass compiler. It meant very little memory was needed to actually do the compilation 08/04/2013 02:37 PM by eti Maybe the pre-processor conditionaly stripps the definition away? 08/04/2013 02:47 PM by Ayende Rahien Eti, Nope, I made sure of that. 08/04/2013 02:50 PM by zdeslav Does dumpbin show the correct symbol in corresponding obj file? 08/04/2013 03:03 PM by Ayende Rahien D:\Work\lightningdb-win\liblmdb\Release [master +10 ~5 -0 !]> &"C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\b in\amd64\dumpbin.exe" /EXPORTS .\mdb.obj Microsoft (R) COFF/PE Dumper Version 11.00.50727.1 Copyright (C) Microsoft Corporation. All rights reserved. Dump of file .\mdb.obj File Type: ANONYMOUS OBJECT D:\Work\lightningdb-win\liblmdb\Release [master +10 ~5 -0 !]> 08/04/2013 03:21 PM by zdeslav are you building with /GL option? also, try /SYMBOLS instead of /EXPORTS. 08/04/2013 03:29 PM by Ayende Rahien zdeslav, I am looking at you now with glazed eyes. No idea what you are talking about. 08/04/2013 03:42 PM by zdeslav sorry for succinctness, I was typing with child in my arms :) i see that you call 'dumpbin /exports' but 'dumpbin /symbols' will list all the symbols, so you can check whether there is anything similar to mdbenvset_flags, or is it missing completely. I ask about /GL flag, as it prevents using these flags. 08/04/2013 03:47 PM by Ayende Rahien I removed /GL flag, and then used /symbols. The object has mdbenvsetflags in it. 08/04/2013 04:06 PM by zdeslav hmm, markdown is messing up the formatting and stripping underscores. I understand that the symbol name in the obj file starts with the underscore, like _mdb_env_set_flags, without any additions (like @12)? In that case it all seems fine. it's a long shot, but are you sure that set_mapsize is linked from the same obj file and not some other? 08/04/2013 09:04 PM by Keith those (env, ....) I'm guessing they should be (&env, ....) 08/04/2013 09:20 PM by Ayende Rahien Keith, No, that is already a pointer. 08/04/2013 09:23 PM by Keith what do the 3 warnings say? 08/04/2013 09:39 PM by Alois Kraus Maybe you have duplicate header files with different content? Check from where the header file is loaded for all projects. Could it be that set_flags does contain as input types ifdefed types which do change the actual signature? That would make it possible to compile it but fail at link time because the library was compiled with a differen set of ifdefs. 08/05/2013 03:34 AM by Kelly Sommers Not enough details in this post to even suggest what the real problem is since I can't see what the project includes. You need to have midl.h and midl.c in the project. Are they included? 08/05/2013 04:13 AM by Ayende Rahien Kelly, That was mostly to vent. I work around that since I just needed to test something out. FWIW, this was in the lmdb-win project. 08/05/2013 09:50 AM by Jono The missing symbol is prefixed with a "_" unlike your usage? 08/05/2013 12:31 PM by Rodrigo Zechin The fact that both functions are defined in the same header doesn't mean they are implemented in the same library. You need to find out on which *.lib file this function is implemented and reference it during the linking phase. The easiest (but ugliest) way of doing this is with a #pragma comment(lib, “xxx.lib”) on your *.c file The "right" way would be to add the lib to your "Additional Dependencies" list on the project properties Comments have been closed on this topic.