# Trying to call GSL function from Fortran program, got errors when trying to compile **URL:** \ **Category:** Help\ **Created:** [September 14, 2022, 3:00pm UTC](https://fortran-lang.discourse.group/t/trying-to-call-gsl-function-from-fortran-program-got-errors-when-trying-to-compile/4314 "2022-09-14T15:00:49Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Aurelius\_Nero](https://avatars.discourse-cdn.com/v4/letter/a/a87d85/32.png) [@Aurelius\_Nero](https://fortran-lang.discourse.group/u/Aurelius_Nero)\ **Post date:** [September 14, 2022, 3:00pm UTC](https://fortran-lang.discourse.group/t/trying-to-call-gsl-function-from-fortran-program-got-errors-when-trying-to-compile/4314/1 "2022-09-14T15:00:49Z")
Hi I just discovered the GNU scientific library, which has a lot of pre written code that one can use. I tried out an example program, just to see and learn how to properly call the gsl functions using the ISO\_C\_BINDING, but I got errors when trying to compile ```auto PROGRAM c_binding_test USE ISO_C_BINDING IMPLICIT NONE INTERFACE GSL_CumulativeChiSq_Prob_Upper FUNCTION gsl_cdf_chisq_Q (x, nu) BIND (C, name="gsl_cdf_chisq_Q") IMPORT REAL (KIND=c_double) :: gsl_cdf_chisq_Q REAL (KIND=c_double), VALUE, INTENT(IN) :: x REAL (KIND=c_double), VALUE,INTENT(IN) :: nu END FUNCTION gsl_cdf_chisq_Q END INTERFACE GSL_CumulativeChiSq_Prob_Upper REAL (KIND=c_double) :: chisq_value REAL (KIND=c_double) :: DoF REAL (KIND=c_double) :: Upper_Tail_Prob PRINT *, "Calculates cumulative upper-tail probability for Chi-Square dis" PRINT *, "Input Chisq value, Degrees of Freedom" READ *, chisq_value,DoF Upper_Tail_Prob = gsl_cdf_chisq_Q (chisq_value,DoF) PRINT *, "Probability is: ",Upper_Tail_Prob END PROGRAM c_binding_test ``` Command used to compile: ```auto gfortran -O3 c_binding_test.f90 -o c_binding_test ``` I get this error: ```auto /usr/bin/ld: /tmp/ccnF6X0E.o: in function `MAIN__': c_binding_test.f90:(.text+0xf1): undefined reference to `gsl_cdf_chisq_Q' collect2: error: ld returned 1 exit status ``` How can I correct this error ? I got the code from here : > ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [September 14, 2022, 3:06pm UTC](https://fortran-lang.discourse.group/t/trying-to-call-gsl-function-from-fortran-program-got-errors-when-trying-to-compile/4314/2 "2022-09-14T15:06:01Z")
You need to also tell the compiler to link to the library containing that function. I.e. include a flag like `-lgnusci` in your compile command, possibly also with `-Lpath/to/lib` to tell it where to find the library. ---
**Author:** ![Aurelius\_Nero](https://avatars.discourse-cdn.com/v4/letter/a/a87d85/32.png) [@Aurelius\_Nero](https://fortran-lang.discourse.group/u/Aurelius_Nero)\ **Post date:** [September 14, 2022, 3:23pm UTC](https://fortran-lang.discourse.group/t/trying-to-call-gsl-function-from-fortran-program-got-errors-when-trying-to-compile/4314/3 "2022-09-14T15:23:46Z")
I used ```auto gfortran -O3 -L/usr/lib64 c_binding_test.f90 -o c_binding_test ``` still obtained an error I installed gsl using the Fedora package manager. (didn’t build it on my own) ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [September 14, 2022, 3:41pm UTC](https://fortran-lang.discourse.group/t/trying-to-call-gsl-function-from-fortran-program-got-errors-when-trying-to-compile/4314/4 "2022-09-14T15:41:27Z")
I’d bet that `/usr/lib64` is already in gfortran’s default library search path, so that one is likely unnecessary. You’re still missing the lowercase `-l` flag though. Possibly `-lgsl`, but you may need to confirm that name. ---
**Author:** ![Aurelius\_Nero](https://avatars.discourse-cdn.com/v4/letter/a/a87d85/32.png) [@Aurelius\_Nero](https://fortran-lang.discourse.group/u/Aurelius_Nero)\ **Post date:** [September 14, 2022, 4:15pm UTC](https://fortran-lang.discourse.group/t/trying-to-call-gsl-function-from-fortran-program-got-errors-when-trying-to-compile/4314/5 "2022-09-14T16:15:47Z")
Got it to work !! Thank you @everythingfunctional for trying. To anyone else trying to get the GSL to work here is what you should do: 1. Follow the steps on this page to download and install the GSL package (I recommend against installing it via the package manager) [How to Install GSL on Linux (Ubuntu, Centros, Redhat, Mac OS) + Simple Installation of gcc Compilers](https://coral.ise.lehigh.edu/jild13/2016/07/11/hello/) a. `wget "https://mirror.ibcp.fr/pub/gnu/gsl/gsl-latest.tar.gz"` b. extract it `tar -zxvf gsl-*.*.tar.gz` c. Enter the directory `cd gsl-*.*` d. make a directory where you want to install the gsl `mkdir /home/yourname/gsl` e. configure the installation to use the new directory `./configure --prefix=/home/yourname/gsl` f. Compile the library `make` h. check the library and test it `make check` i. install the lib `make install` 2. When compiling your files `gfortran -lgsl -lgslcblas -Lhome/yourname/gsl/lib foo.f90 -o foo` 3. Before you run the binary : Add this to your .bashrc ```auto export LD_LIBRARY_PATH=/home/yourname/gsl/lib${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH} ``` 1. Run your binary and you should be ok ! 🙂