I "installed" libprotobuf from Cygwin using the GUI.
However, that step merely downloads a .tar.gz with the actual libraries.
Is there a proper command or location to which to extract it so it's picked up during compilation of software using it?
It downloads the .tar.gz to C:\cygwin64\usr\src\protobuf-3.17.3-1.src
This is what is present in the Cygwin directory
$ find . -name "*protobuf*"
./bin/cygprotobuf-28.dll
./bin/cygprotobuf-lite-28.dll
./etc/setup/libprotobuf28.lst.gz
./usr/src/protobuf-3.17.3-1.src
./usr/src/protobuf-3.17.3-1.src/protobuf-3.17.3-1.cygport
./usr/src/protobuf-3.17.3-1.src/protobuf-3.17.3.tar.gz
You need to install with Cygwin Setup the development package libprotobuf-devel that includes the header and the importlib
additional info
https://cygwin.com/packages/summary/libprotobuf-devel.html
package content
https://cygwin.com/packages/x86_64/libprotobuf-devel/libprotobuf-devel-3.17.3-1
....
2021-07-10 12:51 0 usr/include/
2021-07-10 12:51 0 usr/include/google/
2021-07-10 12:51 0 usr/include/google/protobuf/
2021-07-10 12:51 6365 usr/include/google/protobuf/any.h
2021-07-10 12:51 14209 usr/include/google/protobuf/any.pb.h
2021-07-10 12:51 5916 usr/include/google/protobuf/any.proto
2021-07-10 12:51 52035 usr/include/google/protobuf/api.pb.h
...
2021-07-10 12:51 1293570 usr/lib/libprotobuf-lite.dll.a
2021-07-10 12:51 5033634 usr/lib/libprotobuf.dll.a
2021-07-10 12:51 2563900 usr/lib/libprotoc.dll.a
...