Compiling & linking a Swift/Objective-C++ app via the command line - c++

Question

After adding a C++ component to my Swift application that is being compiled and run via the command line, I now need to compile the C++ and Objective-C++ (*.mm) files and link them with the Swift application.
Makefile:
all: foo-renderer
clean:
rm -f foo-renderer cpp.o objc.o
cpp.o: FooRenderer/FooRenderer/FooLibrary.cpp
clang++ -c -o $# $^
objc.o: cpp.o FooRenderer/FooRenderer/FooLibraryWrapper.mm
clang++ -c -framework Foundation -o $# $^
foo-renderer: objc.o FooRenderer/FooRenderer/*.swift
xcrun -sdk macosx swiftc -import-objc-header FooRenderer/FooRenderer/FooRenderer-Bridging-Header.h -o $# $^
The compiler fails with these errors:
ld: warning: object file (objc.o) was built for newer OSX version (10.12) than being linked (10.9)
Undefined symbols for architecture x86_64:
"__ZN11FooLibrary23printifyERKNSt3__112basic_stringIcNS0_11char_traitsIcEENS0_9allocatorIcEEEE", referenced from:
-[FooLibraryWrapper printify:] in objc.o
"__ZN11FooLibrary8optimizeERKNSt3__112basic_stringIcNS0_11char_traitsIcEENS0_9allocatorIcEEEE", referenced from:
-[FooLibraryWrapper optimize:] in objc.o
"__ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEPKcm", referenced from:
-[FooLibraryWrapper printify:] in objc.o
-[FooLibraryWrapper optimize:] in objc.o
"__ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev", referenced from:
-[FooLibraryWrapper printify:] in objc.o
-[FooLibraryWrapper optimize:] in objc.o
"__ZSt9terminatev", referenced from:
___clang_call_terminate in objc.o
"___cxa_begin_catch", referenced from:
___clang_call_terminate in objc.o
"___gxx_personality_v0", referenced from:
-[FooLibraryWrapper printify:] in objc.o
-[FooLibraryWrapper optimize:] in objc.o
Dwarf Exception Unwind Info (__eh_frame) in objc.o
ld: symbol(s) not found for architecture x86_64
My first instinct was that the standard C++ libraries weren't being included. I tried adding these lib flags to the following command, but to no avail:
cpp.o: FooRenderer/FooRenderer/FooLibrary.cpp
clang++ -c --std=c++14 -lstdc++ -lc++ -stdlib=libstdc++ -o $# $^
What am I missing?

Answer 1

One problem is that cpp.o is missing from the last command line. Adding it to the dependency list should do the trick:
foo-renderer: objc.o FooRenderer/FooRenderer/*.swift cpp.o
xcrun -sdk macosx swiftc -import-objc-header FooRenderer/FooRenderer/FooRenderer-Bridging-Header.h -o $# $^
That's because the linker needs the definitions of the symbols found in the C++ code.
Adding the -l... flags to the command for the cpp.o target is unnecessary because those are linker flags, and at that point you are just compiling.
Also, you likely don't need the cpp.o dependency for the objc.o target, since you are still compiling and compilation doesn't depend on other object files. You could probably do OK without -framework Foundation, but it doesn't hurt anything.

Answer 2

Though I am not very familiar with objc/clang/swift, but i have some pointers for you on how to proceed,
> "__ZN11FooLibrary23printifyERKNSt3__112basic_stringIcNS0_11char_traitsIcEENS0_9allocatorIcEEEE",
> referenced from:
> -[FooLibraryWrapper printify:] in objc.o
The above says that in objc object file in function printify, you have an undefined symbol, which could be FooLibrary::printify::basic_string::char_traits, so most probably you are missing a c++ library, try adding libc++ library in your linking command.
cpp.o: FooRenderer/FooRenderer/FooLibrary.cpp
clang++ -c --std=c++14 -lstdc++ -lc++ -stdlib=libstdc++ -o $# $^
And there is no meaning to add linker flags/libraries during compile time.