Can't compile C++ code: "undefined reference to:"

[Ángel Fernández]

When I try to compile code that did work in previous Kubuntu release, where libarmadillo0 was the package, now I cannot.
Using Ubuntu Oneiric 11.10, and fulfilling the dependences here suggested. Somehow, there may be some missing links.
Packages: libarmadillo2 2.0.1+dfsg-1 0; libarmadillo-dev 2.0.1+dfsg-1 0

This is a g++ compiler output example (I add the flag -larmadillo):

/tmp/ccI9Nbay.o: In function `void arma::lapack::syev<double>(char*, char*, int*, double*, int*, double*, double*, int*, int*)':
program.cpp:(.text._ZN4arma6lapack4syevIdEEvPcS2_PiPT_S3_S5_S5_S3_S3_[void arma::lapack::syev<double>(char*, char*, int*, double*, int*, double*, double*, int*, int*)]+0x45): undefined reference to `dsyev_'

[Julian Taylor (jtaylor)]

this is most likely due to the toolchain transition done in oneiric:
https://wiki.kubuntu.org/NattyNarwhal/ToolchainTransition

read the part about --as-needed

[nobody (conradsand)]

I've confirmed this bug. Indeed it is due to the toolchain transition.

The fix is available in the updated version: Armadillo 2.4.2

I strongly recommend updating the package in Ubuntu.

Upstream:
http://arma.sourceforge.net/download.html

Debian package:
http://packages.debian.org/hu/source/sid/armadillo

[Julian Taylor (jtaylor)]

in what way was it solved in the new version? I can't find a changelog or release notes for it.
to me it looks like an --no-add-needed issue which can only be solved by using e.g. pkg-config which also the new upstream version does not have.

[Julian Taylor (jtaylor)]

ok apparently it is really solved in the new version which should land in precise in a few days.
They probably moved all external function definitions out of the headers.

[Matthias Klose (doko)]

please attach a build log (verbose)

[nobody (conradsand)]

There is no associated build log, as prior to version 2.4.x, Armadillo was a pure C++ template library. The examples provided in the archive are not built by default, hence it is impossible to detect the problem at build time.

In versions prior to 2.4.x, Armadillo relied on a linking trick that no longer works due to the toolchain update. In version 2.4.x, this trick is no longer used.

The associated Armadillo packages in Debian have been fixed and are in the "testing" stream.

Specifically, the fix is in:
"libarmadillo-dev (1:2.4.2+dfsg-2)"
and
"libarmadillo2 (1:2.4.2+dfsg-2)"

http://packages.debian.org/testing/libarmadillo-dev
http://packages.debian.org/testing/libarmadillo2

As such, the armadillo package can now be updated in Ubuntu.

[Julian Taylor (jtaylor)]

do we need a fix for this?
the difference is a bit too large for an easy SRU.

the fix is quite simple, link with some blas providing library.

[Tomas P (em67673)]

Let me put here my workaround (steps 2&3 bellow) for people who could not find any working solution for kubuntu 11.10:

1. apt-get install libarmadillo2 libblas3gf liblapack3gf libarmadillo-dev
2. sudo ln -s /usr/lib/libblas.so.3gf /usr/lib/libblas.so
3. sudo ln -s /usr/lib/liblapack.so.3gf /usr/lib/liblapack.so

then
  g++ test.cpp -larmadillo -lblas -llapack
works. Indeed, the other way
  g++ -larmadillo -lblas -llapack test.cpp
it doesn't (which means in netbeans you need: project properties -> Build -> Linker -> Libraries -> Other Option.)

[Julian Taylor (jtaylor)]

the symlinking should not be necessary, they should be created by blas providing packages via the alternatives mechanism
the second line is wrong in any program, libraries always go behind objects needing their symbols.