Fixing issue #230 a bug for path in file name

Added portable PathSeparator
Fixed format for bp file name

source/adios2/ADIOSTypes.h

@@ -166,6 +166,13 @@ constexpr float DefaultBufferGrowthFactor(1.05f);
  *  2Gb - 100Kb (tolerance)*/
 constexpr size_t DefaultMaxFileBatchSize(2147381248);
 
+constexpr char PathSeparator =
+#ifdef _WIN32
+    '\\';
+#else
+    '/';
+#endif
+
 // adios alias values and types
 constexpr bool DebugON = true;
 constexpr bool DebugOFF = false;

source/adios2/toolkit/format/bp1/BP1Base.cpp

@@ -111,8 +111,11 @@ BP1Base::GetBPNames(const std::vector<std::string> &baseNames) const noexcept
                            const int rank) -> std::string {
 
         const std::string bpBaseName = AddExtension(baseName, ".bp");
-        // name.bp.dir/name.bp.rank
-        const std::string bpName(bpBaseName + ".dir/" + bpBaseName + "." +
+        // path/root.bp.dir/root.bp.rank
+        const std::string bpRootName =
+            bpBaseName.substr(bpBaseName.find_last_of(PathSeparator));
+
+        const std::string bpName(bpBaseName + ".dir/" + bpRootName + "." +
                                  std::to_string(rank));
         return bpName;
     };