Separately typing each library compiles, but a single static library archive fails

Question

I'm trying to build a single library so that it can be linked easily by a single -l switch. Basically If I compile an executable and type out all the libraries my project needs like so:

g++ ncorr_test.cpp -o ncorr_test -I../include -I../../opencv/include/opencv2 -std=c++11 ../lib/ncorr.o ../lib/Strain2D.o ../lib/Disp2D.o ../lib/Data2D.o ../lib/ROI2D.o ../lib/Image2D.o ../lib/Array2D.o `pkg-config opencv --libs` ../../fftw/libs/libfftw3.a ../../SuiteSparse/SPQR/Lib/libspqr.a ../../SuiteSparse/CHOLMOD/Lib/libcholmod.a ../../SuiteSparse/SuiteSparse_config/libsuitesparseconfig.a ../../SuiteSparse/AMD/Lib/libamd.a ../../SuiteSparse/COLAMD/Lib/libcolamd.a ../../lapack/liblapack.a ../../blas/libs/libblas_LINUX.a /usr/lib/gcc/x86_64-linux-gnu/4.8/libgfortran.a

The executable compiles and runs fine. However, when I compile all the libraries together:

ar rvs libncorr.a ../lib/ncorr.o ../lib/Strain2D.o ../lib/Disp2D.o ../lib/Data2D.o ../lib/ROI2D.o ../lib/Image2D.o ../lib/Array2D.o `pkg-config opencv --libs` ../../fftw/libs/libfftw3.a ../../SuiteSparse/SPQR/Lib/libspqr.a ../../SuiteSparse/CHOLMOD/Lib/libcholmod.a ../../SuiteSparse/SuiteSparse_config/libsuitesparseconfig.a ../../SuiteSparse/AMD/Lib/libamd.a ../../SuiteSparse/COLAMD/Lib/libcolamd.a ../../lapack/liblapack.a ../../blas/libs/libblas_LINUX.a /usr/lib/gcc/x86_64-linux-gnu/4.8/libgfortran.a

And then compile like:

g++ ncorr_test.cpp -o ncorr_test -I../include -I../../opencv/include/opencv2 -std=c++11 libncorr.a

I get a bunch of undefined reference errors. I've checked the contents of libncorr.a by using ar -t libncorr.a and it prints out all the libraries I need:

ncorr.o
Strain2D.o
Disp2D.o
Data2D.o
ROI2D.o
Image2D.o
Array2D.o
libopencv_calib3d.so
libopencv_core.so
libopencv_features2d.so
libopencv_flann.so
libopencv_highgui.so
libopencv_imgcodecs.so
libopencv_imgproc.so
libopencv_ml.so
libopencv_objdetect.so
libopencv_photo.so
libopencv_shape.so
libopencv_stitching.so
libopencv_superres.so
libopencv_ts.a
libopencv_video.so
libopencv_videoio.so
libopencv_videostab.so
libopencv_viz.so
libfftw3.a
libspqr.a
libcholmod.a
libsuitesparseconfig.a
libamd.a
libcolamd.a
liblapack.a
libblas_LINUX.a
libgfortran.a

The order of the libraries should be the exact same, so I'm a little lost as to why these undefined references exist. Sorry for the longish code but this is literally what I'm using, so I didn't want to truncate anything and possibly obfuscate the issue. Is there something I'm major I'm missing here?

Answer 1

A static library is just an archive of object files, it's not complete. Whatever external libraries are referenced by the object files in the archive, you need to link with those. Linking with a static library is no different than listing the object files in the archive directly.

You also can't put any other files inside a static library, the linker will not use them.