Small quality of life improvements to basic examples.

examples/hello/bpReader/helloBPReader.cpp

@@ -14,6 +14,7 @@
 
 #include <ios>      //std::ios_base::failure
 #include <iostream> //std::cout
+#include <fstream>  //std::ifstream
 #include <mpi.h>
 #include <stdexcept> //std::invalid_argument std::exception
 #include <vector>
@@ -22,16 +23,25 @@
 
 int main(int argc, char *argv[])
 {
+    // Test if the file has been written by hello_bpWriter:
+    std::string filename = "myVector_cpp.bp";
+    std::ifstream f(filename.c_str());
+    if (!f.good())
+    {
+       std::cerr << "The file " << filename << " does not exist."
+                 << " Presumably this is because hello_bpWriter has not been run. Run ./hello_bpWriter before running this program.\n";
+       return 1;
+    }
+    else
+    {
+       f.close();
+    }
+
     MPI_Init(&argc, &argv);
     int rank, size;
     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
     MPI_Comm_size(MPI_COMM_WORLD, &size);
 
-    /** Application variable */
-    const std::size_t Nx = 10;
-    std::vector<float> myFloats(Nx);
-    std::vector<int> myInts(Nx);
-
     try
     {
         /** ADIOS class factory of IO class objects, DebugON is recommended */
@@ -64,12 +74,15 @@ int main(int argc, char *argv[])
             bpIO.InquireVariable<float>("bpFloats");
         adios2::Variable<int> bpInts = bpIO.InquireVariable<int>("bpInts");
 
+        unsigned long  Nx = 10;
         if (bpFloats) // means found
         {
+            std::vector<float> myFloats;
+
             // read only the chunk corresponding to our rank
             bpFloats.SetSelection({{Nx * rank}, {Nx}});
             // myFloats.data is pre-allocated
-            bpReader.Get<float>(bpFloats, myFloats.data(), adios2::Mode::Sync);
+            bpReader.Get<float>(bpFloats, myFloats, adios2::Mode::Sync);
 
             std::cout << "MyFloats: \n";
             for (const auto number : myFloats)
@@ -81,12 +94,13 @@ int main(int argc, char *argv[])
 
         if (bpInts) // means not found
         {
+            std::vector<int> myInts;
             // read only the chunk corresponding to our rank
             bpInts.SetSelection({{Nx * rank}, {Nx}});
             // myInts.data is pre-allocated
-            bpReader.Get<int>(bpInts, myInts.data(), adios2::Mode::Sync);
+            bpReader.Get<int>(bpInts, myInts, adios2::Mode::Sync);
 
-            std::cout << "MyInts: \n";
+            std::cout << "myInts: \n";
             for (const auto number : myInts)
             {
                 std::cout << number << " ";

examples/hello/bpReader/helloBPReader_nompi.cpp

@@ -11,17 +11,28 @@
 
 #include <ios>       //std::ios_base::failure
 #include <iostream>  //std::cout
+#include <fstream>   //std::fstream
 #include <stdexcept> //std::invalid_argument std::exception
 #include <vector>
 
 #include <adios2.h>
 
 int main(int argc, char *argv[])
 {
-    /** Application variable */
-    const std::size_t Nx = 10;
-    std::vector<float> myFloats(Nx);
-    std::vector<int> myInts(Nx);
+    // Test if the file has been written by hello_bpWriter:
+    std::string filename = "myVector_cpp.bp";
+    std::ifstream f(filename.c_str());
+    if (!f.good())
+    {
+       std::cerr << "The file " << filename << " does not exist."
+                 << " Presumably this is because hello_bpWriter has not been run. Run ./hello_bpWriter before running this program.\n";
+       return 1;
+    }
+    else
+    {
+       f.close();
+    }
+
 
     try
     {
@@ -34,7 +45,7 @@ int main(int argc, char *argv[])
 
         /** Engine derived class, spawned to start IO operations */
         adios2::Engine bpReader =
-            bpIO.Open("myVector_cpp.bp", adios2::Mode::Read);
+            bpIO.Open(filename.c_str(), adios2::Mode::Read);
 
         /** Write variable for buffering */
         adios2::Variable<float> bpFloats =
@@ -44,12 +55,23 @@ int main(int argc, char *argv[])
 
         if (bpFloats)
         {
-            bpReader.Get<float>(bpFloats, myFloats.data(), adios2::Mode::Sync);
+            std::vector<float> myFloats;
+            bpReader.Get<float>(bpFloats, myFloats, adios2::Mode::Sync);
+            std::cout << "Float vector inside " << filename << ": {";
+            for (auto & x : myFloats) {
+              std::cout << x << ", ";
+            }
+            std::cout << "}\n";
         }
 
         if (bpInts)
         {
-            bpReader.Get<int>(bpInts, myInts.data(), adios2::Mode::Sync);
+            std::vector<int> myInts;
+            bpReader.Get<int>(bpInts, myInts, adios2::Mode::Sync);
+        }
+        else
+        {
+            std::cout << "There are no integer datasets in " << filename << ".\n";
         }
 
         /** Close bp file, engine becomes unreachable after this*/

examples/hello/bpWriter/helloBPWriter.cpp

@@ -53,9 +53,10 @@ int main(int argc, char *argv[])
         adios2::Variable<std::string> bpString =
             bpIO.DefineVariable<std::string>("bpString");
 
+        std::string filename = "myVector_cpp.bp";
         /** Engine derived class, spawned to start IO operations */
         adios2::Engine bpFileWriter =
-            bpIO.Open("myVector_cpp.bp", adios2::Mode::Write);
+            bpIO.Open(filename, adios2::Mode::Write);
 
         /** Put variables for buffering, template type is optional */
         bpFileWriter.Put<float>(bpFloats, myFloats.data());
@@ -64,6 +65,7 @@ int main(int argc, char *argv[])
 
         /** Create bp file, engine becomes unreachable after this*/
         bpFileWriter.Close();
+        std::cout << "Wrote file " << filename << " to disk. It can now be read by running ./bin/hello_bpReader.\n";
     }
     catch (std::invalid_argument &e)
     {

examples/hello/bpWriter/helloBPWriter_nompi.cpp

@@ -35,15 +35,17 @@ int main(int argc, char *argv[])
         adios2::Variable<float> bpFloats = bpIO.DefineVariable<float>(
             "bpFloats", {}, {}, {Nx}, adios2::ConstantDims);
 
+        std::string filename = "myVector_cpp.bp";
         /** Engine derived class, spawned to start IO operations */
         adios2::Engine bpWriter =
-            bpIO.Open("myVector_cpp.bp", adios2::Mode::Write);
+            bpIO.Open(filename, adios2::Mode::Write);
 
         /** Write variable for buffering */
         bpWriter.Put<float>(bpFloats, myFloats.data());
 
         /** Create bp file, engine becomes unreachable after this*/
         bpWriter.Close();
+        std::cout << "Wrote file " << filename << " to disk. It can now be read by running ./bin/hello_bpReader.\n";
     }
     catch (std::invalid_argument &e)
     {