Adding json library to clang libtooling project - c++

Question

I am writing a RecursiveASTVisitor using clang libtool.
Right now I'm trying to read in a json file and have downloaded the json library from https://github.com/open-source-parsers/jsoncpp
I have copied over the folder "include/json" to my project path "llvm/tools/clang/include"
When compiling using the ninja command, the include command isn't throwing any error include "json/json.h"
However, when I try entering a line of code Json::Value root, it throws a linking error..
Full error log:
ninja -v
[1/1] : && /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Werror=date-time -std=c++11 -fcolor-diagnostics -fno-common -Woverloaded-virtual -Wno-nested-anon-types -g -Wl,-search_paths_first -Wl,-headerpad_max_install_names tools/clang/tools/extra/myASTChecker/CMakeFiles/MyASTChecker.dir/MyASTChecker.cpp.o -o bin/MyASTChecker lib/libLLVMSupport.a lib/libclangTooling.a lib/libclangASTMatchers.a lib/libclangFormat.a lib/libclangFrontend.a lib/libclangDriver.a lib/libLLVMOption.a lib/libclangParse.a lib/libLLVMMCParser.a lib/libclangSerialization.a lib/libclangSema.a lib/libclangEdit.a lib/libclangAnalysis.a lib/libLLVMBitReader.a lib/libLLVMProfileData.a lib/libclangToolingCore.a lib/libclangAST.a lib/libclangRewrite.a lib/libclangLex.a lib/libclangBasic.a lib/libLLVMCore.a lib/libLLVMMC.a lib/libLLVMSupport.a -lcurses -lpthread -lz -lm -Wl,-rpath,#executable_path/../lib && :
FAILED: bin/MyASTChecker
: && /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Werror=date-time -std=c++11 -fcolor-diagnostics -fno-common -Woverloaded-virtual -Wno-nested-anon-types -g -Wl,-search_paths_first -Wl,-headerpad_max_install_names tools/clang/tools/extra/myASTChecker/CMakeFiles/MyASTChecker.dir/MyASTChecker.cpp.o -o bin/MyASTChecker lib/libLLVMSupport.a lib/libclangTooling.a lib/libclangASTMatchers.a lib/libclangFormat.a lib/libclangFrontend.a lib/libclangDriver.a lib/libLLVMOption.a lib/libclangParse.a lib/libLLVMMCParser.a lib/libclangSerialization.a lib/libclangSema.a lib/libclangEdit.a lib/libclangAnalysis.a lib/libLLVMBitReader.a lib/libLLVMProfileData.a lib/libclangToolingCore.a lib/libclangAST.a lib/libclangRewrite.a lib/libclangLex.a lib/libclangBasic.a lib/libLLVMCore.a lib/libLLVMMC.a lib/libLLVMSupport.a -lcurses -lpthread -lz -lm -Wl,-rpath,#executable_path/../lib && :
Undefined symbols for architecture x86_64:
"Json::Value::Value(Json::ValueType)", referenced from:
MyASTFrontendAction::CreateASTConsumer(clang::CompilerInstance&, llvm::StringRef) in MyASTChecker.cpp.o
"Json::Value::~Value()", referenced from:
MyASTFrontendAction::CreateASTConsumer(clang::CompilerInstance&, llvm::StringRef) in MyASTChecker.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
What am I missing or should be doing instead??

Answer 1

When compiling using the ninja command, the include command isn't throwing any error include "json/json.h"
When you copy paste the header files into a folder that's already in the compiler's include search path. You won't get issues in #include "json/json.h" because yeah the file is there and you haven't used anything from it yet so it's just some function, class declarations which will be ignored.
However, when I try entering a line of code Json::Value root, it throws a linking error.
Now, when wrote Json::Value root; what happened was that you called the constructor for Json::Value which is declared in the included header files, but is implemented in the source files. Hence, the compiler is not able to find that implementation of the constructor and is complaining about it.
It might have worked the whole Json parser library was implemented in the included header files. As then the compiler would have found the declaration with the definition.
What you really want to do is have the include files in the compiler's include search directory and then a compiled library file of json parser, which you link to your ASTVisitor.
Resolution:
First of all, I will discourage copy pasting json parsers include files into clang's include directory. Instead, you can do two things here:
Paste your include files in a general include directory like /usr/local/include
Add your include directory to CPLUS_INCLUDE_PATH.
Once you have that include files setup done, you will want to have the json parser from github compiled and then link your recursiveASTVisitor to it.
Answer
I see that jsonparser you linked has a cmakelist file which is really helpful if you just want to let it do the job.
once you clone the repo, do as they say to compile their library.
mkdir -p build/debug
cd build/debug
cmake -DCMAKE_BUILD_TYPE=debug -DBUILD_STATIC_LIBS=ON -DBUILD_SHARED_LIBS=OFF -DARCHIVE_INSTALL_DIR=. -G "Unix Makefiles" ../..
make
After this you can call sudo make install this will copy the include files in a proper include directory which is indexed for search by your OS and also do the same for the compiled library. After this linking to your library is as simple as
CFLAGS = `pkg-config --cflags opencv`
LIBS = `pkg-config --libs opencv`
% : %.cpp
g++ $(CFLAGS) $(LIBS) -o $# $<
if you using MAKEFILE to compile your ASTVisitor (make ASTvisitor.cpp). OR
target_link_library(target jsoncpp)
if you are using a CMAKELIST to compile your ASTVisitor