1. Link Against the GSL Libraries
When we compile code with GSL, we need to tell the linker to include the GSL libraries. For example, modify our compile command from
1 | g++ -o cal-cpp-beta-to-theta cal-cpp-beta-to-theta.cpp |
to
1 | g++ -o cal-cpp-beta-to-theta cal-cpp-beta-to-theta.cpp -lgsl -lgslcblas -lm |
Here’s what each flag does:
-lgsl : Links the GNU Scientific Library.
-lgslcblas : Links the GSL CBLAS library (required by GSL for some BLAS routines).
-lm : Links the math library, which is sometimes needed for functions defined in
<cmath>.
2. Ensure GSL Is Installed
If we haven’t installed GSL yet, on a Debian-based system (like Ubuntu) we can install it with:
1 | sudo apt-get install libgsl-dev |
This installs the development headers and libraries needed for compiling and linking against GSL.
3. Order of Linker Arguments
The order of linker arguments is important: all library flags (starting with -l) should come after our source files. In the corrected compile command above, the libraries follow the source file.
4. Recompile the Code
After we’ve installed GSL (if it wasn’t already installed) and updated our compile command, recompile our code. The linker should now be able to find the necessary GSL functions, and the “undefined reference” errors should be resolved.
Summary
our original linking command doesn’t include the GSL libraries, which is why the linker complains about missing symbols (such as gsl_root_fsolver_brent, gsl_root_fsolver_alloc, etc.). Adding the proper flags (-lgsl -lgslcblas -lm) to our compile command should fix the error.