compilation - how is linking done in c++? -

i using proxygen library facebook build simple client example . in directory have 2 object files how link them : using:

g++ -std=c++11 -o my_echo curlclientmain.o  curlclient.o -lproxygenhttpserver -lfolly -lglog -lgflags -pthread 

i think ma missing linker flag -lgflags in above example. maybe after including -someflag out compilation . how know possilble library flags posiible 1 have used -lproxyhttpserver.

in short these libs defined or located. using ubuntu.

here error message

 in function `main': /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:91: undefined reference `proxygen::httpconnector::httpconnector(proxygen::httpconnector::callback*, folly::hhwheeltimer*)' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:102: undefined reference `proxygen::httpconnector::connect(folly::eventbase*, folly::socketaddress const&, std::chrono::duration<long, std::ratio<1l, 1000l> >, std::map<folly::asyncsocket::optionkey, int, std::less<folly::asyncsocket::optionkey>, std::allocator<std::pair<folly::asyncsocket::optionkey const, int> > > const&, folly::socketaddress const&)' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:91: undefined reference `proxygen::httpconnector::~httpconnector()' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:99: undefined reference `proxygen::httpconnector::connectssl(folly::eventbase*, folly::socketaddress const&, std::shared_ptr<folly::sslcontext> const&, ssl_session_st*, std::chrono::duration<long, std::ratio<1l, 1000l> >, std::map<folly::asyncsocket::optionkey, int, std::less<folly::asyncsocket::optionkey>, std::allocator<std::pair<folly::asyncsocket::optionkey const, int> > > const&, folly::socketaddress const&, std::string const&)' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:91: undefined reference `proxygen::httpconnector::~httpconnector()' curlclient.o: in function `curlservice::curlclient::connectsuccess(proxygen::httpupstreamsession*)': /home/kshitij/proxygen/httpclient/samples/curl/curlclient.cpp:69: undefined reference `proxygen::httpupstreamsession::newtransaction(proxygen::httptransactionhandler*)' collect2: error: ld returned 1 exit status kshitij@forgetit:~/proxygen/httpclient/samples/curl$ g++ -std=c++11 -o my_echo curlclientmain.o  curlclient.o -lproxygenhttpserver -lfolly -lglog -lgflags -pthread curlclientmain.o: in function `main': /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:91: undefined reference `proxygen::httpconnector::httpconnector(proxygen::httpconnector::callback*, folly::hhwheeltimer*)' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:102: undefined reference `proxygen::httpconnector::connect(folly::eventbase*, folly::socketaddress const&, std::chrono::duration<long, std::ratio<1l, 1000l> >, std::map<folly::asyncsocket::optionkey, int, std::less<folly::asyncsocket::optionkey>, std::allocator<std::pair<folly::asyncsocket::optionkey const, int> > > const&, folly::socketaddress const&)' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:91: undefined reference `proxygen::httpconnector::~httpconnector()' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:99: undefined reference `proxygen::httpconnector::connectssl(folly::eventbase*, folly::socketaddress const&, std::shared_ptr<folly::sslcontext> const&, ssl_session_st*, std::chrono::duration<long, std::ratio<1l, 1000l> >, std::map<folly::asyncsocket::optionkey, int, std::less<folly::asyncsocket::optionkey>, std::allocator<std::pair<folly::asyncsocket::optionkey const, int> > > const&, folly::socketaddress const&, std::string const&)' /home/kshitij/proxygen/httpclient/samples/curl/curlclientmain.cpp:91: undefined reference `proxygen::httpconnector::~httpconnector()' curlclient.o: in function `curlservice::curlclient::connectsuccess(proxygen::httpupstreamsession*)': /home/kshitij/proxygen/httpclient/samples/curl/curlclient.cpp:69: undefined reference `proxygen::httpupstreamsession::newtransaction(proxygen::httptransactionhandler*)' collect2: error: ld returned 1 exit status 

how know possilble library flags posiible 1 have used -lproxyhttpserver.

it depends on compilation environment.

you appear use gnu compiler in linux. there tool list installed shared libraries:

ldconfig -p 

you list of lines this

libpthread.so.0 (libc6,x86-64, os abi: linux 2.6.32) => /lib/x86_64-linux-gnu/libpthread.so.0 

remove lib prefix , extension .so.x , name of library. in case it's pthread. link libray use option -lname. so, -lpthread in example.

in short these libs defined or located

the righthand part of => full path library.