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I installed jsoncpp on ubuntu with 'sudo apt-get install libjsoncpp-dev' and tried to run a minimalistic test program:

#include <iostream>
#include <fstream>
#include <jsoncpp/json/json.h>
int main()
    ifstream file("example.json");
    Json::Value value;
    Json::Reader reader;
    reader.parse(file,value);
    cout << value << endl;
I'm using a makefile to compile my code with the following flags:
CC=g++
CXXFLAGS=-std=c++17 -fopenmp -O3 -ljsoncpp
The following errors occur:
/usr/bin/ld: /tmp/cc4MbV6f.o: in function `Test_JsonWriter()':
test.cpp:(.text+0x5865): undefined reference to `Json::Value::Value(Json::ValueType)'
/usr/bin/ld: test.cpp:(.text+0x5872): undefined reference to `Json::Reader::Reader()'
/usr/bin/ld: test.cpp:(.text+0x5885): undefined reference to `Json::Reader::parse(std::istream&, Json::Value&, bool)'
/usr/bin/ld: test.cpp:(.text+0x5894): undefined reference to `Json::operator<<(std::ostream&, Json::Value const&)'
/usr/bin/ld: test.cpp:(.text+0x5a9f): undefined reference to `Json::Value::~Value()'
/usr/bin/ld: /tmp/cc4MbV6f.o: in function `Test_JsonWriter() [clone .cold]':
test.cpp:(.text.unlikely+0x6bf): undefined reference to `Json::Value::~Value()'
collect2: error: ld returned 1 exit status
make: *** [Makefile:21: test] Error 1
I also made sure to update all packages etc. Also including '#include <jsoncpp/json/value.h>' doesn't help either.
Any idea what is wrong? Thanks for the help.
                Is your include statement correct? The GitHub example shows : #include "json/json.h" .. github.com/open-source-parsers/jsoncpp/blob/master/example/…
– FreudianSlip
                Mar 9, 2022 at 9:19
                You probably included another copy of JsonCpp in your project (aside from the system's one) and now you are using the headers of one version while trying to link to another version. Either use only the system's version and remove everything else or use only the included copy, which you then have to build and link together with the rest of your project instead of linking with -ljsoncpp.
– user17732522
                Mar 9, 2022 at 9:22
                Alternatively you have placed the flags incorrectly. -ljsoncpp must be placed after the names of the .cpp files or .o files on the compiler invocation (which you aren't showing) and ususally doesn't belong in CXXFLAGS, but a LDLIBS variable.
– user17732522
                Mar 9, 2022 at 9:27
                Hi Tom, glad it worked!  I guess that a nice thing to do would be to upvote the "solution" comment...
– Aname
                Mar 9, 2022 at 11:02
        
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