Hi, I am attempting to develop a QT app using pjsip in windows. But I can not add pjsip library in QT. I was compiling the pjsip using mingw. After, pjsip library and include names added in qmake file as below. QT 4.7.4 MİNGW compiler build project when adding only header file like pjsua2.hpp ,pjlib.h etc . However I adding class such as Endpoint in QT code , QT gives error that is undefined reference to `pj::Endpoint::Endpoint()'.I checked the libraries names and paths.But they are right. What is the reason of this error? best regards. *QT += core gui* *TARGET = testpj2* *TEMPLATE = app* *DEFINES += PJ_NATIVE_STRING_IS_UNICODE=0 \* * PJ_WIN32=1 \* * PJ_IS_LITTLE_ENDIAN=1 \* * PJ_IS_BIG_ENDIAN=0 \* *DEFINES -= UNICODE* *SOURCES += main.cpp\* * mainwindow.cpp* *HEADERS += mainwindow.h* *FORMS += mainwindow.ui* *INCLUDEPATH += $$PWD/pjproject-2.4/pjsip/include \* * $$PWD/pjproject-2.4/pjlib/include \* * $$PWD/pjproject-2.4/pjlib-util/include \* * $$PWD/pjproject-2.4/pjmedia/include \* * $$PWD/pjproject-2.4/pjnath/include* *LIBS += -L$$PWD/pjproject-2.4/lib \* * -llibpjproject-i386-Win32-vc8-Release-Dynamic \* * -lpjlib-util-i386-Win32-vc8-Release-Dynamic \* * -lpjsua2-lib-i386-Win32-vc8-Release-Dynamic \* * -lpjsua-lib-i386-Win32-vc8-Release-Dynamic \* * -lpjsip-ua-i386-Win32-vc8-Release-Dynamic \* * -lpjsip-simple-i386-Win32-vc8-Release-Dynamic \* * -lpjsip-core-i386-Win32-vc8-Release-Dynamic \* * -lpjmedia-codec-i386-Win32-vc8-Release-Dynamic \* * -lpjmedia-i386-Win32-vc8-Release-Dynamic \* * -lpjmedia-codec-i386-Win32-vc8-Release-Dynamic \* * -lpjmedia-audiodev-i386-Win32-vc8-Release-Dynamic \* * -lpjnath-i386-Win32-vc8-Release-Dynamic \* * -lpjlib-i386-Win32-vc8-Release-Dynamic \* * -llibbaseclasses-i386-Win32-vc8-Release-Dynamic \* * -llibg7221codec-i386-Win32-vc8-Release-Dynamic \* * -llibportaudio-i386-Win32-vc8-Release-Dynamic \* * -llibgsmcodec-i386-Win32-vc8-Release-Dynamic \* * -llibilbccodec-i386-Win32-vc8-Release-Dynamic \* * -llibspeex-i386-Win32-vc8-Release-Dynamic \* * -llibresample-i386-Win32-vc8-Release-Dynamic \* * -llibmilenage-i386-Win32-vc8-Release-Dynamic \* * -llibsrtp-i386-Win32-vc8-Release-Dynamic \* * -lwinmm \* * -lole32 \* * -lws2_32 \* * -lwsock32 \* * -lgdi32*