如何获得通过终端编译的 C++ 代码以使用 Qt IDE 进行编译？

Question

My general question is how can I get C++ code that compiles when I issue

g++ <my_program>.cpp -o my_program -O3 -ffast-math -lm -llapack -lgsl -lgslcblas

to build using the Qt IDE. The C++ code I have is written by my physics advisor and is for research that I'm conducting under his guidance, and I would like to be able to use a visual environment for changes I have to make. At the moment, my specific issue is (outside of the hundreds of warnings) one of the header files references several lapacke library functions that cause an "undefined reference" error. The offending line is:

template <>
int tensor<double>::find_eigenvalues()
  {
   // some code
   // for loop
      {
         dsyevr_ (&JOBZ, &RANGE, &UPLO, &SIZE, A, &SIZE, &VLU, &VLU, &ILU, &ILU, &ABSTOL, &M, 
                  (double *)(obj->eval), Z, &LDZ, ISUPPZ, WORK, &LWORK, IWORK, &LIWORK, &INFO) ;
      }
   // more code
  }

Above this function definition appears

extern "C" void dsyevr_ (char *, char *, char *, int *, double *, int *, double *, double *,
                         int *, int *, double *, int *, double *, double *, int *, int *,
                         double *, int *, int *, int *, int *) ;

Now, if I explicitly include the lapacke header file #include "lapacke.h" I can get rid of that error. However, a new one pops up. I get a "conflicting type" error from the line

extern "C" void zheevr_ (char *, char *, char *, int *, complex *, int *, double *, double *, int *, int *, double *, int *, double *,
              complex *, int *, int *, complex *, int *, double *, int *, int *, int *, int *) ;

which is also a function that is defined in the lapacke.h header file. Any help is appreciated!

My coding level would be school taught, but over 20 years since I've had a course in C++. I'm ok with basic notions, though.

My version of Linux is: Ubuntu 18.04.5 x86_64. The g++ compiler version is: g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0; which is also the kit I have selected for Qt.

Answer 1

I would strongly advise you to use CMake ( https://cmake.org/ ) to compile your project instead of using direct calls to the compiler. Using CMake will make it compatible with the QtCreator IDE while keeping it compilable through a command line as well. CMake also manages dependencies such as your external libraries and is the most widely used build tool for C++. You can find many example to help you getting started if needed. There are other build tools compatible with QtCreator, such as QMake or Qbs, but both are (unfortunately) less used than CMake.

For your specific linking issue, you might need to add a -L option to locate your library file. (-L for the lib path, -l for the lib name).

In CMake, the commands that will interest you specifically are:

add_executable(..)
target_link_libraries(..)
target_include_directories(..)