Static library built for archive which is not the architecture being linked (x86_64)

Question

I am experiencing what seems to be the same problem when I try to compile two different programs. Each of them creates first a static library and then the main application linki

Answer 1

A possible cause is using the GNU ar(1)/ranlib(1) instead of the ones supplied by the Xcode toolchain. Run which -a ar and which -a ranlib to see the what you have in $PATH.

For example:

$ which -a ranlib
/usr/local/bin/ranlib
/usr/bin/ranlib

$ /usr/local/bin/ranlib --version
GNU ranlib (GNU Binutils) 2.28.51.20170105
Copyright (C) 2017 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

$ /usr/bin/ralib --version
error: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: unknown option character `-' in: --version
Usage: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib [-sactfqLT] [-] archive [...]

Same for ar. If you're like me and had /usr/local/bin preceeding /usr/bin in $PATH, with the GNU tools in /usr/local/bin and the Xcode ones in /usr/bin, you can fix it with:

cd /usr/local/bin
mv ar gar
ln -s /usr/bin/ar ar
mv ranlib granlib
ln -s /usr/bin/ranlib ranlib