Qt cannot find the header files

[Hassan-math]

Hi All,

I'm running a simple code using libigl (a simple geometry library) and Eigen libraries. So, I added their paths in the .pro file by

INCLUDEPATH += "[mypath]/C_libraries/libigl/include" 
INCLUDEPATH += "[mypath]/C_libraries/eigen/Eigen"

The above paths are the libraries' directories. All the header files are available in the mentioned paths. But when I trying following code, Qt cannot find header files:

#include <igl/cotmatrix.h>
#include <Eigen/Dense>
#include <Eigen/Sparse>
#include <iostream>

int main()
{
  Eigen::MatrixXd V(4,2);
  V<<0,0,
     1,0,
     1,1,
     0,1;
  Eigen::MatrixXi F(2,3);
  F<<0,1,2,
     0,2,3;
  Eigen::SparseMatrix<double> L;
  igl::cotmatrix(V,F,L);
  std::cout<<"Hello, mesh: "<<std::endl<<L*V<<std::endl;
  return 0;
}

Qt can find first header (cotmatrix.h from igl), but for next one I got following error:

error: Eigen/Dense: No such file or directory
12 | #include <Eigen/Dense>
| ^~~~~~~~~~~~~

could you please let me know why does it happen? How can I resolve it?
I'm using Ubuntu 20.4 on iMac machine.

[Bonnie]

Do you have "[mypath]/C_libraries/eigen/Eigen/Eigen/Dense" file? (That's three eigen OMG...)
I think your include path might should be "[mypath]/C_libraries/eigen"

[Hassan-math]

@Bonnie Hi, that's not three eigen. It's "[mypath]/C_libraries/eigen/Eigen/Dense". Yes, its available in the mentioned directory. I tried "[mypath]/C_libraries/eigen", but it cannot find the header files.

[jsulm]

@Hassan-math You should try with "[mypath]/C_libraries" as it is trying to include "#include <Eigen/Dense>"...

[Hassan-math]

@jsulm I tried, but it doesn't work. Same error...

[Bonnie]

@Hassan-math said in Qt cannot find the header files:

It's "[mypath]/C_libraries/eigen/Eigen/Dense".

Then it should be "[mypath]/C_libraries/eigen".
Rerun qmake after you modify the .pro file, better also clean and rebuild.

Tip:
If you use "[mypath]/C_libraries/eigen/Eigen" as include path, then you should only

#include <Dense>
#include <Sparse>

But this will have problems if the header files includes <Eigen/xx> in themselves.

[jsulm]

@Hassan-math You should do a complete clean rebuild after changing pro file: delete build folder, run qmake and build.

[Hassan-math]

@jsulm and @Bonnie Thank you. Yes, it works. When I rebuilt it, it's resolved. The path "[mypath]/C_libraries/eigen" works for me...