C++ linker errors, Undefined references to Items that should be referenced from a Share Object_问答_开发者

I am building a library, called physgameengine, to aid in building games. This game library links against several libraries, including: Ogre3d, Bullet Physics and SDL, which are in the library files libOgreMain-1.6.5.so, libBulletCollision.a, libBulletDynamics.a, libBulletSoftBody.a, libSDL-1.2.so.0. This Library/Shared object appears to build just fine in Ubuntu 9.10, using GCC and Code::blocks. It does build fine on windows with mingw and Code::blocks.

In windows I can make games that compile/link using the library I built just fine, those programs run and do exactly what I expect it to. In Ubuntu when I try to compile/link a game that uses this Library I am making I get lots of undefined reference errors. But none to the functions or objects in the library I built, but rather to the items that my library calls. Here is an example of the errors I get.

> ||warning: libOgreMain-1.6.5.so, needed by ../physgameengine/bin/ubuntudebug/libphysgame.so, not found (try using -rpath or -rpath-link)|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::Root(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::StringUtil::BLANK'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::updateAabbs()'|
../physgameengine/开发者_开发知识库bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::createRenderWindow(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned int, unsigned int, bool, std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > const*)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Timer::getMilliseconds()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::createSceneManager(unsigned short, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::~Root()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::~btCollisionWorld()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::renderOneFrame()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionObject::btCollisionObject()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Timer::getMillisecondsCPU()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btSimulationIslandManager::buildAndProcessIslands(btDispatcher*, btCollisionWorld*, btSimulationIslandManager::IslandCallback*)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Viewport::getActualWidth() const'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::initialise(bool, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Camera::lookAt(Ogre::Vector3 const&)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::removeCollisionObject(btCollisionObject*)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Viewport::getActualHeight() const'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Timer::reset()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::restoreConfig()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Timer::~Timer()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::NedAllocImpl::deallocBytes(void*)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::convexSweepTest(btConvexShape const*, btTransform const&, btTransform const&, btCollisionWorld::ConvexResultCallback&, float) const'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::NedAllocImpl::allocBytes(unsigned int, char const*, int, char const*)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `typeinfo for btCollisionWorld'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionObject::~btCollisionObject()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btSimulationIslandManager::btSimulationIslandManager()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Root::showConfigDialog()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionObject::setActivationState(int)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::LogManager::getSingleton()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::performDiscreteCollisionDetection()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::LogManager::logMessage(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Ogre::LogMessageLevel, bool)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Timer::Timer()'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::btCollisionWorld(btDispatcher*, btBroadphaseInterface*, btCollisionConfiguration*)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `typeinfo for btCollisionObject'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `Ogre::Camera::setPosition(Ogre::Vector3 const&)'|
../physgameengine/bin/ubuntudebug/libphysgame.so||undefined reference to `btCollisionWorld::addCollisionObject(btCollisionObject*, short, short)'|
||=== Build finished: 36 errors, 1 warnings ===|

The bulk of the code is identical between windows and Linux they seem to have equivalent compile/linker settings. But the Linux game appears to be linking against the original libraries that my library should be linking against. What is going on? Any Ideas on how to fix it?

Unlike in Windows, in Linux systems it's not enough to place a shared library file into the same folder as executable.

You should either provide an LD_LIBRARY_PATH variable or follow the linker's advice and use -rpath (check this question)

The very first line of your error tells you the problem:

libOgreMain-1.6.5.so, needed by libphysgame.so, not found (try using -rpath or -rpath-link)|

You need to specify the directory where libOgreMain is installed. Since you need to use a linker option, you need to use the -Wl feature of gcc. Assuming the files is in /opt/lib, you would add:

gcc -Wl,-rpath-link,/opt/lib ...rest of linker line...

Just based on the first line:

> ||warning: libOgreMain-1.6.5.so, needed by ../physgameengine/bin/ubuntudebug/libphysgame.so, not found (try using -rpath or -rpath-link)|

It looks like your linker is having trouble finding your shared object. Check to make sure your linker's include paths are properly set up.

This is a good link on the subject http://sysprogs.com/w/fixing-rpath-link-issues-with-cross-compilers/

Essentially if you do not have -lmylib for all your libraries you link to, you cannot count on -Lpath to find them. Thus, if /opt/infoa/lib/liba.so depends on /opt/infod/lib/libd.so and you only specify -la, then you need something like this:

gcc -Wl,-rpath-link,/opt/infod/lib -L/opt/infoa/lib -la *.c -o myexec