Undefined references problem when compiling c++ test code

Answered

September 11, 2020 01:37

Hello. I have been experiencing multiple undefined reference problems when trying to compile a very simple c++ source code. In fact, the code is the same as "mip1_c++.cpp", except that I changed "#include "gurobi_c++.h" to "#include "/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/include/gurobi_c++.h" that it is where the file it is in my system.

The first three error lines are:

copy_mip1_c++.cpp:(.text+0x2b): undefined reference to GRBEnv::GRBEnv(bool)
copy_mip1_c++.cpp:(.text+0x44): undefined reference to GRBModel::GRBModel(GRBEnv const&)
copy_mip1_c++.cpp:(.text+0x8d): undefined reference to GRBModel::addVar(double, double, double, char, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)

I also added the lib dir to my ld.so.conf:

/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/lib

and then executed ldconfig, to make the system aware of changes on it.

Yet, these error messages persist. What shall I do to solve it? Thanks for your time

Comments

11 comments

Official comment
Simranjit Kaur

Gurobi Staff

December 06, 2024 00:41
This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
Matthias Miltenberger

Gurobi Staff

September 11, 2020 11:34 Edited
Hi Alexandre,

You should not modify the include instructions in the code but rather tell the compiler where to find the include directory via:
```
g++ -I/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/include/
```
The same holds for library paths:
```
g++ -L/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/lib
```
You might want to check out CMake for a more human-readable way of defining build and compile instructions.

Cheers,
Matthias
0

Alexandre Faria

September 11, 2020 22:20

Hello. I tried to compile the original mip1 with:

g++ -I/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/include/
  -L/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/lib/
  -o mip1_c++ mip1_c++.cpp

But the same errors keep showing up:

/tmp/ccLVCNbc.o: In function `main':
mip1_c++.cpp:(.text+0x2b): undefined reference to `GRBEnv::GRBEnv(bool)'
mip1_c++.cpp:(.text+0x44): undefined reference to `GRBModel::GRBModel(GRBEnv const&)'
mip1_c++.cpp:(.text+0x8d): undefined reference to `GRBModel::addVar(double, double, double, char, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'

Thomas Opfer

September 12, 2020 07:53
Undefined references mean that you forgot the library in the compiler command. I am not sure which library is missing, but I guess it is libgurobi_c++.a, so try adding -lgurobi_c++ to the end of your compiler command.
0
Matthias Miltenberger

Gurobi Staff

September 14, 2020 06:16
Thomas is correct. The commands or compiler options in my previous post only set additional paths to look for headers and libraries - you still need to specify the actual libraries, though, via
-lgurobi_c++ -lgurobi90
0

Alexandre Faria

September 14, 2020 21:43

Ok, this time I tried with:

g++ -I/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/include/
  -L/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/lib
  -lgurobi_c++ -lgurobi90 -o mip1_c++ mip1_c++.cpp

and received: /usr/bin/ld: cannot find -lgurobi90

Looking for it with sudo find /media/34GB/Arquivos-de-Programas-Linux/gurobi801/ -name gurobi90* returns no result. Where it is (or should be?)

If I omit the gurobi90, keeping everything else equal, I still receive the same:

mip1_c++.cpp:(.text+0x2b): undefined reference to `GRBEnv::GRBEnv(bool)'
mip1_c++.cpp:(.text+0x44): undefined reference to `GRBModel::GRBModel(GRBEnv const&)'
mip1_c++.cpp:(.text+0x8d): undefined reference to `GRBModel::addVar(double, double, double, char, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'

Thomas Opfer

September 15, 2020 04:50
For Gurobi 8.0, it might be -lgurobi80 .
0
Alexandre Faria

September 16, 2020 00:42
True, however, the problem withstands. Any ideas?
0

Thomas Opfer

September 16, 2020 05:34 Edited

As I said, please put the libraries at the end of the command. Please try

g++ -I/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/include/
  -L/media/34GB/Arquivos-de-Programas-Linux/gurobi801/linux64/lib
  -o mip1_c++ mip1_c++.cpp -lgurobi_c++ -lgurobi80

Alexandre Faria

September 18, 2020 00:14
Thanks, it did work. What -lgurobi_c++ and -lgurobi80 does that -L/... does not? I mean, -L already points to /lib, where libgurobi.so.8.0.1 and libgurobi_g++4.2.a are....
0
Matthias Miltenberger

Gurobi Staff

September 18, 2020 08:09 Edited
Dear Alexandre,

The explanation is literally a simple online search for "gcc linking" away:
https://www.rapidtables.com/code/linux/gcc/gcc-l.html

Programming can be pretty hard and complicated at times, especially when working with lower-level languages like C and C++. You should probably try to complete some tutorial classes to get a better understanding of the general concepts and to avoid future frustrations and road blocks. I highly recommend checking out Python for a more user-friendly experience.

Also, please upgrade to Gurobi version 9. I don't see any reason for starting with an outdated version that is superseded by another version 8 release. At the very least, you should be using Gurobi 8.1.1 if you really need to work with version 8.

Please don't get me wrong - I really want to help you and don't want to sound discouraging!

All the best,
Matthias
1

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Undefined references problem when compiling c++ test code

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