Hi, In My Project i need bar-code scanning. so i use zxing library but i m heaving some linking error and its getting me crazy. error is

 Undefined symbols:
  "zxing::BinaryBitmap::BinaryBitmap(zxing::Ref<zxing::Binarizer>)", referenced from:
      -[Decoder decode:] in Decoder.o
  "zxing::LuminanceSource::LuminanceSource()", referenced from:
      GrayBytesMonochromeBitmapSource::GrayBytesMonochromeBitmapSource(unsigned char const*, int, int, int)in GrayBytesMonochromeBitmapSource.o
  "zxing::qrcode::QRCodeReader::decode(zxing::Ref<zxing::BinaryBitmap>)", referenced from:
      -[Decoder decode:] in Decoder.o
  "zxing::LuminanceSource::~LuminanceSource()", referenced from:
      GrayBytesMonochromeBitmapSource::~GrayBytesMonochromeBitmapSource()in GrayBytesMonochromeBitmapSource.o
      GrayBytesMonochromeBitmapSource::~GrayBytesMonochromeBitmapSource()in GrayBytesMonochromeBitmapSource.o
  "zxing::ReaderException::~ReaderException()", referenced from:
      -[Decoder decode:] in Decoder.o
      -[Decoder decode:] in Decoder.o
  "zxing::String::getText()", referenced from:
      -[Decoder decode:] in Decoder.o
  "typeinfo for zxing::LuminanceSource", referenced from:
      typeinfo for GrayBytesMonochromeBitmapSourcein GrayBytesMonochromeBitmapSource.o
  "vtable for zxing::IllegalArgumentException", referenced from:
      __ZTVN5zxing24IllegalArgumentExceptionE$non_lazy_ptr in Decoder.o
  "typeinfo for zxing::ReaderException", referenced from:
      GCC_except_table1 in Decoder.o
  "vtable for zxing::Exception", referenced from:
      __ZTVN5zxing9ExceptionE$non_lazy_ptr in Decoder.o
  "zxing::LuminanceSource::copyMatrix()", referenced from:
      vtable for GrayBytesMonochromeBitmapSourcein GrayBytesMonochromeBitmapSource.o
  "zxing::Result::getText()", referenced from:
      -[Decoder decode:] in Decoder.o
  "zxing::GlobalHistogramBinarizer::GlobalHistogramBinarizer(zxing::Ref<zxing::LuminanceSource>)", referenced from:
      -[Decoder decode:] in Decoder.o
  "zxing::IllegalArgumentException::~IllegalArgumentException()", referenced from:
      -[Decoder decode:] in Decoder.o
      -[Decoder decode:] in Decoder.o
  "zxing::Result::getResultPoints()", referenced from:
      -[Decoder decode:] in Decoder.o
  "typeinfo for zxing::IllegalArgumentException", referenced from:
      GCC_except_table1 in Decoder.o
  "zxing::Exception::what() const", referenced from:
      -[Decoder decode:] in Decoder.o
      -[Decoder decode:] in Decoder.o
  "vtable for zxing::ReaderException", referenced from:
      __ZTVN5zxing15ReaderExceptionE$non_lazy_ptr in Decoder.o
  "zxing::qrcode::QRCodeReader::QRCodeReader()", referenced from:
      -[Decoder decode:] in Decoder.o
  "zxing::qrcode::QRCodeReader::~QRCodeReader()", referenced from:
      -[Decoder decode:] in Decoder.o
      -[Decoder decode:] in Decoder.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
       "zxing::BinaryBitmap::BinaryBitmap(zxing::Ref<zxing::Binarizer>)", referenced from:
           -[Decoder decode:] in Decoder.o
       "zxing::LuminanceSource::LuminanceSource()", referenced from:
           GrayBytesMonochromeBitmapSource::GrayBytesMonochromeBitmapSource(unsigned char const*, int, int, int)in GrayBytesMonochromeBitmapSource.o
       "zxing::qrcode::QRCodeReader::decode(zxing::Ref<zxing::BinaryBitmap>)", referenced from:
           -[Decoder decode:] in Decoder.o
       "zxing::LuminanceSource::~LuminanceSource()", referenced from:
           GrayBytesMonochromeBitmapSource::~GrayBytesMonochromeBitmapSource()in GrayBytesMonochromeBitmapSource.o
           GrayBytesMonochromeBitmapSource::~GrayBytesMonochromeBitmapSource()in GrayBytesMonochromeBitmapSource.o
       "zxing::ReaderException::~ReaderException()", referenced from:
           -[Decoder decode:] in Decoder.o
           -[Decoder decode:] in Decoder.o
       "zxing::String::getText()", referenced from:
           -[Decoder decode:] in Decoder.o
       "typeinfo for zxing::LuminanceSource", referenced from:
           typeinfo for GrayBytesMonochromeBitmapSourcein GrayBytesMonochromeBitmapSource.o
       "vtable for zxing::IllegalArgumentException", referenced from:
           __ZTVN5zxing24IllegalArgumentExceptionE$non_lazy_ptr in Decoder.o
       "typeinfo for zxing::ReaderException", referenced from:
           GCC_except_table1 in Decoder.o
       "vtable for zxing::Exception", referenced from:
           __ZTVN5zxing9ExceptionE$non_lazy_ptr in Decoder.o
       "zxing::LuminanceSource::copyMatrix()", referenced from:
           vtable for GrayBytesMonochromeBitmapSourcein GrayBytesMonochromeBitmapSource.o
       "zxing::Result::getText()", referenced from:
           -[Decoder decode:] in Decoder.o
       "zxing::GlobalHistogramBinarizer::GlobalHistogramBinarizer(zxing::Ref<zxing::LuminanceSource>)", referenced from:
           -[Decoder decode:] in Decoder.o
       "zxing::IllegalArgumentException::~IllegalArgumentException()", referenced from:
           -[Decoder decode:] in Decoder.o
           -[Decoder decode:] in Decoder.o
       "zxing::Result::getResultPoints()", referenced from:
           -[Decoder decode:] in Decoder.o
       "typeinfo for zxing::IllegalArgumentException", referenced from:
           GCC_except_table1 in Decoder.o
       "zxing::Exception::what() const", referenced from:
           -[Decoder decode:] in Decoder.o
           -[Decoder decode:] in Decoder.o
       "vtable for zxing::ReaderException", referenced from:
           __ZTVN5zxing15ReaderExceptionE$non_lazy_ptr in Decoder.o
       "zxing::qrcode::QRCodeReader::QRCodeReader()", referenced from:
           -[Decoder decode:] in Decoder.o
       "zxing::qrcode::QRCodeReader::~QRCodeReader()", referenced from:
           -[Decoder decode:] in Decoder.o
           -[Decoder decode:] in Decoder.o
     ld: symbol(s) not found
     collect2: ld returned 1 exit status

i m trying to resolve this for last two day. i think i m missing some library or some file. can any one point me out what i m doing wrong.

Usman