Compiling problem with libxml2

ld returns 1 exit status during make proccess after configure the code:

mv -f .deps/helloworld.Tpo .deps/helloworld.Po
/bin/bash ../../libtool --tag=CXX --mode=link g++ -g -O2 ../../libbats.la -lxml2 -lsigc-2.0 -o helloworld init.o think.o helloworld.o
libtool: link: g++ -g -O2 -o .libs/helloworld init.o think.o helloworld.o ../../.libs/libbats.so -lxml2 /usr/lib/x86_64-linux-gnu/libsigc-2.0.so
../../.libs/libbats.so: undefined reference to `xmlXPathFreeObject'
../../.libs/libbats.so: undefined reference to `xmlDocGetRootElement'
../../.libs/libbats.so: undefined reference to `xmlXPathNewContext'
../../.libs/libbats.so: undefined reference to `xmlXIncludeProcessFlags'
../../.libs/libbats.so: undefined reference to `xmlHasProp'
../../.libs/libbats.so: undefined reference to `xmlXPathFreeContext'
../../.libs/libbats.so: undefined reference to `xmlXPathEvalExpression'
../../.libs/libbats.so: undefined reference to `xmlReadFile'
../../.libs/libbats.so: undefined reference to `xmlFreeDoc'
../../.libs/libbats.so: undefined reference to `xmlCheckVersion'
../../.libs/libbats.so: undefined reference to `xmlNodeGetContent'
../../.libs/libbats.so: undefined reference to `xmlCleanupParser'
../../.libs/libbats.so: undefined reference to `xmlGetProp'
../../.libs/libbats.so: undefined reference to `xmlFree'
collect2: error: ld returned 1 exit status
make[2]: *** [helloworld] Error 1
make[2]: Leaving directory `/home/danialbehzadi/Documents/Sources/libbats-2.0.1/examples/helloworld'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/danialbehzadi/Documents/Sources/libbats-2.0.1/examples'
make: *** [all-recursive] Error 1