From 59a32fb3a8a8548c9df3668373c9b5c6f5235fee Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Thu, 22 Apr 2021 08:06:58 -0600
Subject: [PATCH] Check whether the output directory exists.

---
 examples/step-70/step-70.cc | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/examples/step-70/step-70.cc b/examples/step-70/step-70.cc
index 011964a3e1..720055aa72 100644
--- a/examples/step-70/step-70.cc
+++ b/examples/step-70/step-70.cc
@@ -144,6 +144,7 @@ namespace LA
 #endif
 
 #include <cmath>
+#include <filesystem>
 #include <fstream>
 #include <iostream>
 #include <memory>
@@ -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)
@@ -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
-- 
2.39.5