g++ compilation undefined references on external hpp file - c++

Question

I am trying to include pugixml.hpp in my code using the following include notation :
#include "pugixml-1.7/src/pugixml.hpp"
Now the weird thing is, this runs in Codeblocks fine, but when I am trying to run it via terminal (I have all the source codes in one single file) using g++ :
g++-5 -v -std=c++11 -03 -Wall -pedantic -fopenmp -pthread main.cpp -o main.o
It throws out a bunch of undefined reference to pugi::xml.. (whichever the api I was using). I have tried everything, by keeping the pugixml.hpp file in the main directory, by adding bunch of flags like -iquote or -c to point to that directory.. but nothing is working. What else I should try? I am including the output till directory search here :
Using built-in specs.
COLLECT_GCC=g++-5
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.2.1-23ubuntu1~12.04' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=gcc4-compatible --disable-libstdcxx-dual-abi --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.2.1 20151031 (Ubuntu 5.2.1-23ubuntu1~12.04)
COLLECT_GCC_OPTIONS='-v' '-std=c++11' '-O3' '-Wall' '-Wpedantic' '-fopenmp' '-pthread' '-o' 'main.o' '-shared-libgcc' '-mtune=generic' '-march=x86-64' '-pthread'
/usr/lib/gcc/x86_64-linux-gnu/5/cc1plus -quiet -v -imultiarch x86_64-linux-gnu -D_GNU_SOURCE -D_REENTRANT main.cpp -quiet -dumpbase main.cpp -mtune=generic -march=x86-64 -auxbase main -O3 -Wall -Wpedantic -std=c++11 -version -fopenmp -fstack-protector -Wformat-security -o /tmp/ccXfMWIT.s
GNU C++11 (Ubuntu 5.2.1-23ubuntu1~12.04) version 5.2.1 20151031 (x86_64-linux-gnu)
compiled by GNU C version 5.2.1 20151031, GMP version 5.0.2, MPFR version 3.1.0-p3, MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/5"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/5/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/5
/usr/include/x86_64-linux-gnu/c++/5
/usr/include/c++/5/backward
/usr/lib/gcc/x86_64-linux-gnu/5/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/5/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.

Answer 1

You need to link against the compiled pugixml library. Including the pugixml.hpp is simply telling the preprocessor to get the interface, however the compiler (more specifically the linker) needs to find the appropriate compiled pugixml code for it to be usable from your source code.