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[C++17] Check whether the output directory exists. #12080

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Jul 4, 2023
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[C++17] Check whether the output directory exists. #12080

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18 changes: 16 additions & 2 deletions examples/step-70/step-70.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -144,6 +144,7 @@ namespace LA
#endif

#include <cmath>
#include <filesystem>
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That'll be some fun - For libstdc++ we will have to figure out a sane way to decide whether we have to link against libstdc++fs as well or not.

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Shouldn't -std=c++17 imply that?

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@bangerth gcc version 9 onwards should just require -std=c++17, gcc version 8 and older require manual linking with libstdc++fs. At least if I recall correctly 😸

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I remember that I had similar issues with gcc8. I solved this by substitution with boost libraries:

#ifdef __cpp_lib_filesystem
#  include <filesystem>
namespace filesystem
{
  using namespace std::filesystem;
}
#else
#  include <boost/filesystem.hpp>
namespace filesystem
{
  using namespace boost::filesystem;
}
#endif

I'm not sure if the __cpp_lib_filesystem flag only exists for gcc.

We could move this code snippet into the std_cxx17 namespace. What do you think?

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The problem is that we don't include the boost filesystem parts in the bundled/ directory :-( There is also the issue that this is a tutorial and I really didn't want to introduce some complicated workaround in tutorials -- I'd rather just leave things as they are if we can't do it right....

#include <fstream>
#include <iostream>
#include <memory>
Expand Down Expand Up @@ -769,8 +770,11 @@ namespace Step70

// In the constructor, we create the mpi_communicator as well as
// the triangulations and dof_handler for both the fluid and the solid.
// Using the mpi_communicator, both the ConditionalOStream and TimerOutput
// Using the `mpi_communicator`, both the ConditionalOStream and TimerOutput
// object are constructed.
//
// In the constructor, we also check whether the output directory
// specified in the input file exists and, if not, create it.
template <int dim, int spacedim>
StokesImmersedProblem<dim, spacedim>::StokesImmersedProblem(
const StokesImmersedProblemParameters<dim, spacedim> &par)
Expand All @@ -792,7 +796,17 @@ namespace Step70
Triangulation<dim, spacedim>::smoothing_on_coarsening))
, fluid_dh(fluid_tria)
, solid_dh(solid_tria)
{}
{
if (std::filesystem::exists(par.output_directory))
{
Assert(std::filesystem::is_directory(par.output_directory),
ExcMessage("You specified <" + par.output_directory +
"> as the output directory in the input file, "
"but this is not in fact a directory."));
}
else
std::filesystem::create_directory(par.output_directory);
}


// In order to generate the grid, we first try to use the functions in the
Expand Down