undefined symbol error

[eugene]

I'm trying to compile and run some c++ code to be called from Matlab
(mex file)
and I'm getting "Invalid MEX-file ... undefined symbol" error. Anybody
knows
where to look for solution?

-> g++ -c ... abc.cpp
-> gcc -c ... /usr/local/matlab701/extern/src/mexversion.c
-> g++ ... -o abc.mexglx abc.o mexversion.o ... -L/home/eugene/lib
.... -lxyz ...

No errors so far.

??? Invalid MEX-file '/home/eugene/matlab/abc.mexglx':
/home/eugene/lib/libxyz.so: undefined symbol: xyz_debug.

Code for libxyz.so has:
extern int xyz_debug;

abc.cpp has:
int xyz_debug = 0;

 

[mlimber]

I'm trying to compile and run some c++ code to be called from Matlab
(mex file)
and I'm getting "Invalid MEX-file ... undefined symbol" error. Anybody
knows
where to look for solution?

A MATLAB newsgroup or on the MathWorks website would probably be better
places to start. This group is for discussing C++ language issues, not
third-party tools.

Cheers! --M

 

[eugene]

A MATLAB newsgroup or on the MathWorks website would probably be better
places to start. This group is for discussing C++ language issues, not
third-party tools.

Cheers! --M

Been there, done that
MathWorks website: do c++ at your own risk
MATLAB newsgroup: this is c/c++ problem

- symbol xyz_debug is defined in abc.cpp as "int xyz_debug = 0;"
- symbol xyz_debug is referenced in libxyz.so as "extern int
xyz_debug;"
The question is why after
-> g++ -c ... abc.cpp
-> gcc -c ... /usr/local/matlab701/extern/src/mexversion.c
-> g++ ... -o abc.mexglx abc.o mexversion.o ... -L/home/eugene/lib
.... -lxyz ...
try to run and got "undefined symbol xyz_debug" error?

 

[=?iso-8859-1?Q?Ali_=C7ehreli?=]

- symbol xyz_debug is defined in abc.cpp as "int xyz_debug = 0;"
- symbol xyz_debug is referenced in libxyz.so as "extern int
xyz_debug;"
The question is why after
-> g++ -c ... abc.cpp
-> gcc -c ... /usr/local/matlab701/extern/src/mexversion.c
-> g++ ... -o abc.mexglx abc.o mexversion.o ... -L/home/eugene/lib
... -lxyz ...
try to run and got "undefined symbol xyz_debug" error?

Try putting abc.o after -lxyz. If I'm not mistaken, the linker looks for
symbols in the successive files.

Ali

 

[eugene]

Try putting abc.o after -lxyz. If I'm not mistaken, the linker looks for
symbols in the successive files.

Ali

Still no luck.

g++ ... -Wl,-y,xyz_debug ... -lxyz ... abc.o ...
/home/eugene/lib/libxyz.so: reference to xyz_debug
abc.o: definition of xyz_debug

with same runtime error "undefined symbol xyz_debug".

Any ideas?

 

[=?iso-8859-1?Q?Ali_=C7ehreli?=]

Try putting abc.o after -lxyz. If I'm not mistaken, the linker looks for
symbols in the successive files.

Ali

Still no luck.

g++ ... -Wl,-y,xyz_debug ... -lxyz ... abc.o ...
/home/eugene/lib/libxyz.so: reference to xyz_debug
abc.o: definition of xyz_debug

with same runtime error "undefined symbol xyz_debug".

Any ideas?

I wonder whether you are running against C vs. C++ linkage issues. If
xyz_debug has C linkage in libxyz.so, like because of being declared in a C
file, you have to define it as

extern "C" int xyz_debug = 0;

in abc.cpp.

Ali

 

[eugene]

I wonder whether you are running against C vs. C++ linkage issues. If
xyz_debug has C linkage in libxyz.so, like because of being declared in a C
file, you have to define it as

extern "C" int xyz_debug = 0;

in abc.cpp.

Ali

I was trying this. Does not work
Because libxyz.so is based on c++
Thanks anyway

 

[Jay Nabonne]

mlimber wrote:
- symbol xyz_debug is defined in abc.cpp as "int xyz_debug = 0;"
- symbol xyz_debug is referenced in libxyz.so as "extern int
xyz_debug;"
The question is why after
-> g++ -c ... abc.cpp
-> gcc -c ... /usr/local/matlab701/extern/src/mexversion.c
-> g++ ... -o abc.mexglx abc.o mexversion.o ... -L/home/eugene/lib
... -lxyz ...
try to run and got "undefined symbol xyz_debug" error?

This seems like a gcc problem, not a MATLAB one. It's having problems
resolving a symbol in the .so file when the .so is being loaded at
runtime. You could probably reproduce this without MATLAB.

So, I would suggest running this by a gcc newgroup.

- Jay

 

[Jay Nabonne]

Another thought: what happens if you reverse where the int is defined
(i.e. define it in the .so and make it extern from abc.cpp)?

- Jay

 

[eugene]

This seems like a gcc problem, not a MATLAB one. It's having problems
resolving a symbol in the .so file when the .so is being loaded at
runtime. You could probably reproduce this without MATLAB.

Program like abc.cpp (same definition / reference for xyz_debug) was
successfully
compiled and ran outside Matlab.

It looks as the problem is due to the way Matlab loads external code.
My hope
was that c++ folks would point out how to link the code so that
definition and
reference for xyz_debug would be in order.

- Eugene

 

[eugene]

Another thought: what happens if you reverse where the int is defined
(i.e. define it in the .so and make it extern from abc.cpp)?

- Jay

Cannot do that, libxyz.so is not mine and it's not open source

- Eugene