diff --git a/file_io/include/aare/FileInterface.h b/file_io/include/aare/FileInterface.h
index bb93393..fe02699 100644
--- a/file_io/include/aare/FileInterface.h
+++ b/file_io/include/aare/FileInterface.h
@@ -9,7 +9,7 @@ public:
     //  - w writing (overwrites existing file)
     //  - a appending (appends to existing file)
     // TODO! do we need to support w+, r+ and a+?
-    FileInterface(std::filesystem::path& fname, const char* opts="r" ){}; 
+    FileInterface(const std::filesystem::path& fname, const char* opts="r" ){}; 
     
     // write one frame
     virtual void write(Frame& frame) = 0;
diff --git a/file_io/include/aare/FileInterface.hpp b/file_io/include/aare/FileInterface.hpp
index 7e2dfb6..c8774af 100644
--- a/file_io/include/aare/FileInterface.hpp
+++ b/file_io/include/aare/FileInterface.hpp
@@ -83,7 +83,7 @@ class FileInterface {
 
   public:
     std::string mode;
-    std::filesystem::path m_fname;
+    // std::filesystem::path m_fname;
     std::filesystem::path m_base_path;
     std::string m_base_name, m_ext;
     int m_findex;
diff --git a/file_io/include/aare/NumpyFile.hpp b/file_io/include/aare/NumpyFile.hpp
index 7f8192f..90da019 100644
--- a/file_io/include/aare/NumpyFile.hpp
+++ b/file_io/include/aare/NumpyFile.hpp
@@ -4,15 +4,21 @@
 #include "aare/defs.hpp"
 #include <iostream>
 #include <numeric>
+#include <filesystem>
 
 namespace aare{
 
 class NumpyFile : public FileInterface {
     FILE *fp = nullptr;
     size_t initial_header_len = 0;
+    
 
 
   public:
+    std::filesystem::path m_fname; //TO be made private!
+
+    NumpyFile(const std::filesystem::path& fname);
+    NumpyFile(FileConfig, header_t);
     void write(Frame &frame) override;
     Frame read() override { return get_frame(this->current_frame++); }
 
@@ -29,8 +35,6 @@ class NumpyFile : public FileInterface {
     ssize_t cols() const override { return header.shape[2]; }
     ssize_t bitdepth() const override { return header.dtype.bitdepth(); }
 
-    NumpyFile(std::filesystem::path fname);
-    NumpyFile(FileConfig, header_t);
     header_t header;
     uint8_t major_ver_{};
     uint8_t minor_ver_{};
diff --git a/file_io/include/aare/RawFile.hpp b/file_io/include/aare/RawFile.hpp
index 59300db..5630e40 100644
--- a/file_io/include/aare/RawFile.hpp
+++ b/file_io/include/aare/RawFile.hpp
@@ -9,8 +9,10 @@ namespace aare {
 class RawFile : public FileInterface {
 
     using config = RawFileConfig;
+    
 
   public:
+    std::filesystem::path m_fname; //TO be made private!
     void write(Frame &frame) override{};
     Frame read() override { return get_frame(this->current_frame++); };
     std::vector<Frame> read(size_t n_frames) override;
diff --git a/file_io/src/NumpyFile.cpp b/file_io/src/NumpyFile.cpp
index 0d7df8d..9b4f63d 100644
--- a/file_io/src/NumpyFile.cpp
+++ b/file_io/src/NumpyFile.cpp
@@ -3,19 +3,8 @@
 
 namespace aare{
 
-void NumpyFile::write(Frame &frame) {
-    if (fp == nullptr) {
-        throw std::runtime_error("File not open");
-    }
-    if (not(mode == "w" or mode == "a")) {
-        throw std::runtime_error("File not open for writing");
-    }
-    fseek(fp, 0, SEEK_END);
-    fwrite(frame._get_data(), frame.size(), 1, fp);
-}
-
-NumpyFile::NumpyFile(std::filesystem::path fname_) {
-    this->m_fname = fname_;
+NumpyFile::NumpyFile(const std::filesystem::path& fname) {
+    this->m_fname = fname;
     fp = fopen(this->m_fname.c_str(), "rb");
 }
 NumpyFile::NumpyFile(FileConfig config, header_t header) {
@@ -36,6 +25,19 @@ NumpyFile::NumpyFile(FileConfig config, header_t header) {
         aare::NumpyHelpers::write_header(std::filesystem::path(this->m_fname.c_str()), this->header);
 }
 
+void NumpyFile::write(Frame &frame) {
+    if (fp == nullptr) {
+        throw std::runtime_error("File not open");
+    }
+    if (not(mode == "w" or mode == "a")) {
+        throw std::runtime_error("File not open for writing");
+    }
+    fseek(fp, 0, SEEK_END);
+    fwrite(frame._get_data(), frame.size(), 1, fp);
+}
+
+
+
 Frame NumpyFile::get_frame(size_t frame_number) {
     Frame frame(header.shape[1], header.shape[2], header.dtype.bitdepth());
     get_frame_into(frame_number, frame._get_data());