diff --git a/lib/tdm_datamodel.hpp b/lib/tdm_datamodel.hpp
index fd28b31..0ef9bb1 100644
--- a/lib/tdm_datamodel.hpp
+++ b/lib/tdm_datamodel.hpp
@@ -119,23 +119,172 @@ static std::string join_strings(std::vector<std::string> &thestring, const char*
 
 // https://zone.ni.com/reference/de-XX/help/370858P-0113/tdmdatamodel/tdmdatamodel/tdm_header_tdx_data/
 
-// define mapping of locally supported datatypes to tdm datatypes
-typedef short int eInt16Usi;
-typedef int eInt32Usi;
-typedef unsigned char eUInt8Usi;
-typedef unsigned short int eUInt16Usi;
-typedef unsigned int eUInt32Usi;
-typedef float eFloat32Usi;
-typedef double eFloat64Usi;
+// define mapping of C++ supported datatypes to tdm datatypes
 
-enum class tdmdatatype {
-  eInt16Usi,
-  eInt32Usi,
-  eUInt8Usi,
-  eUInt16Usi,
-  eUInt32Usi,
-  eFloat32Usi,
-  eFloat64Usi
+// define mapping of locally supported datatypes to tdm datatypes
+// typedef short int eInt16Usi;
+// typedef int eInt32Usi;
+// typedef unsigned char eUInt8Usi;
+// typedef unsigned short int eUInt16Usi;
+// typedef unsigned int eUInt32Usi;
+// typedef float eFloat32Usi;
+// typedef double eFloat64Usi;
+
+// enum class tdmdatatype {
+//   eInt16Usi,
+//   eInt32Usi,
+//   eUInt8Usi,
+//   eUInt16Usi,
+//   eUInt32Usi,
+//   eFloat32Usi,
+//   eFloat64Usi
+// };
+
+// base class for all tdm datatypes
+class tdmdatatype
+{
+protected:
+  short int sint16_;
+  int sint32_;
+  unsigned char uint8_;
+  unsigned short int uint16_;
+  unsigned int uint32_;
+  float float32_;
+  double float64_;
+public:
+  tdmdatatype(): sint16_(0), sint32_(0),
+                 uint8_(0), uint16_(0), uint32_(0),
+                 float32_(0.0), float64_(0.0) {};
+  friend std::ostream& operator<<(std::ostream& out, const tdmdatatype& num)
+  {
+    return num.print(out);
+  }
+  virtual std::ostream& print(std::ostream& out) const
+  {
+    out<<"tdmdatatype";
+    return out;
+  }
+};
+
+class eInt16Usi: public tdmdatatype
+{
+public:
+  eInt16Usi() { }
+  eInt16Usi(short int num) { sint16_ = num; }
+  // eInt16Usi& operator=(const eInt16Usi &num)
+  // {
+  //   // self-assignment check
+  //   if ( this != &num)
+  //   {
+  //     this->sint16_ = num.sint16_;
+  //   }
+	// 	return *this;
+  // }
+  friend std::ostream& operator<<(std::ostream& out, const eInt16Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<sint16_;
+    return out;
+  }
+};
+
+class eInt32Usi: public tdmdatatype
+{
+public:
+  eInt32Usi() { }
+  eInt32Usi(int num) { sint32_ = num; }
+  friend std::ostream& operator<<(std::ostream& out, const eInt32Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<sint32_;
+    return out;
+  }
+};
+
+class eUInt8Usi: public tdmdatatype
+{
+public:
+  eUInt8Usi() { }
+  eUInt8Usi(int num) { uint8_ = num; }
+  friend std::ostream& operator<<(std::ostream& out, const eUInt8Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<uint8_;
+    return out;
+  }
+};
+
+class eUInt16Usi: public tdmdatatype
+{
+public:
+  eUInt16Usi() { }
+  eUInt16Usi(int num) { uint16_ = num; }
+  friend std::ostream& operator<<(std::ostream& out, const eUInt16Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<uint16_;
+    return out;
+  }
+};
+
+class eUInt32Usi: public tdmdatatype
+{
+public:
+  eUInt32Usi() { }
+  eUInt32Usi(int num) { uint32_ = num; }
+  friend std::ostream& operator<<(std::ostream& out, const eUInt32Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<uint32_;
+    return out;
+  }
+};
+
+class eFloat32Usi: public tdmdatatype
+{
+public:
+  eFloat32Usi() { }
+  eFloat32Usi(int num) { float32_ = num; }
+  friend std::ostream& operator<<(std::ostream& out, const eFloat32Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<float32_;
+    return out;
+  }
+};
+
+class eFloat64Usi: public tdmdatatype
+{
+public:
+  eFloat64Usi() { }
+  eFloat64Usi(int num) { float64_ = num; }
+  friend std::ostream& operator<<(std::ostream& out, const eFloat64Usi& num)
+  {
+    return num.print(out);
+  }
+  std::ostream& print(std::ostream& out) const override
+  {
+    out<<float64_;
+    return out;
+  }
 };
 
 struct tdm_datatype {
diff --git a/lib/tdm_reaper.cpp b/lib/tdm_reaper.cpp
index ba2ddda..7df25df 100644
--- a/lib/tdm_reaper.cpp
+++ b/lib/tdm_reaper.cpp
@@ -567,7 +567,9 @@ std::string tdm_reaper::get_block_overview(format formatter)
 
 // -------------------------------------------------------------------------- //
 
-std::vector<double> tdm_reaper::get_channel(std::string &id)
+// extract channel by id
+template<typename tdmtype>
+std::vector<tdmtype> tdm_reaper::get_channel(std::string& id)
 {
   // check for existence of required channel id (=key)
   if ( tdmchannels_.count(id) == 1 )
@@ -576,39 +578,108 @@ std::vector<double> tdm_reaper::get_channel(std::string &id)
     tdm_channel chn = tdmchannels_.at(id);
 
     // extract (first) "localcolumn" for channel
+    if ( chn.local_columns_.size() != 1 )
+    {
+      throw std::runtime_error(std::string("invalid local_columns_ of channel: ") + id);
+    }
     localcolumn loccol = localcolumns_.at(chn.local_columns_[0]);
 
+    if ( loccol.sequence_representation_ != "explicit" )
+    {
+      throw std::runtime_error(std::string("unsupported sequence_representation: ")
+                                + loccol.sequence_representation_);
+    }
+
     // use "values" id to map to external block
     block blk = tdx_blocks_.at(loccol.external_id_);
-
-    // declare buffer covering the required range of "tdxbuffer_"
-    std::vector<unsigned char> blkbuff( tdxbuffer_.begin()+blk.byte_offset_,
-                                        tdxbuffer_.begin()+blk.byte_offset_
-                                         + blk.length_*sizeof(double)        );
-
-    std::vector<double> datvec(blk.length_);
-    this->convert_data_to_type<double>(blkbuff,datvec);
-
-    return datvec;
+    
+    // // distinguish numeric datatypes
+    // switch ( blk.value_type_ )
+    // {
+    //   case "eInt16Usi" :
+    //     break;
+    //   case "eInt32Usi" :
+    //     break;
+    //   case "eUInt8Usi" :
+    //     break;
+    //   case "eUInt16Usi" :
+    //     break;
+    //   case "eUInt32Usi" :
+    //     break;
+    //   case "eFloat32Usi" :
+    //     // declare buffer covering the required range of "tdxbuffer_"
+    //     std::vector<unsigned char> blkF32( tdxbuffer_.begin()+blk.byte_offset_,
+    //                                         tdxbuffer_.begin()+blk.byte_offset_
+    //                                          + blk.length_*sizeof(eFloat32Usi) );
+    //     std::vector<eFloat32Usi> datvecF32(blk.length_);
+    //     this->convert_data_to_type<eFloat32Usi>(blkF32,datvecF32);
+    //     return datvecF32;
+    //     break;
+    //   case "eFloat64Usi" :
+    //     // declare buffer covering the required range of "tdxbuffer_"
+    //     std::vector<unsigned char> blkF64( tdxbuffer_.begin()+blk.byte_offset_,
+    //                                         tdxbuffer_.begin()+blk.byte_offset_
+    //                                          + blk.length_*sizeof(eFloat64Usi) );
+    //     std::vector<eFloat64Usi> datvecF64(blk.length_);
+    //     this->convert_data_to_type<eFloat64Usi>(blkF64,datvecF64);
+    //     return datvecF64;
+    //     break;
+    //   case "eStringUsi" :
+    //     throw std::runtime_error("datatype 'eStringUsi' is not supported");
+    //     break;
+    // }
   }
   else
   {
     throw std::invalid_argument(std::string("channel id does not exist: ") + id);
   }
+
+  return std::vector<tdmtype>();
 }
 
+template std::vector<tdmdatatype> tdm_reaper::get_channel<tdmdatatype>(std::string& id);
+
+// std::vector<double> tdm_reaper::get_channel(std::string &id)
+// {
+//   // check for existence of required channel id (=key)
+//   if ( tdmchannels_.count(id) == 1 )
+//   {
+//     // retrieve full channel info
+//     tdm_channel chn = tdmchannels_.at(id);
+//
+//     // extract (first) "localcolumn" for channel
+//     localcolumn loccol = localcolumns_.at(chn.local_columns_[0]);
+//
+//     // use "values" id to map to external block
+//     block blk = tdx_blocks_.at(loccol.external_id_);
+//
+//     // declare buffer covering the required range of "tdxbuffer_"
+//     std::vector<unsigned char> blkbuff( tdxbuffer_.begin()+blk.byte_offset_,
+//                                         tdxbuffer_.begin()+blk.byte_offset_
+//                                          + blk.length_*sizeof(double)        );
+//
+//     std::vector<double> datvec(blk.length_);
+//     this->convert_data_to_type<double>(blkbuff,datvec);
+//
+//     return datvec;
+//   }
+//   else
+//   {
+//     throw std::invalid_argument(std::string("channel id does not exist: ") + id);
+//   }
+// }
+
 void tdm_reaper::print_channel(std::string &id, const char* filename)
 {
   std::ofstream fou(filename);
 
-  std::vector<double> chn = this->get_channel(id);
+  std::vector<double> chn; // = this->get_channel(id);
 
   for ( auto el: chn ) fou<<el<<"\n";
 
   fou.close();
 }
 
-
 // -------------------------------------------------------------------------- //
 
 template<typename datatype>
diff --git a/lib/tdm_reaper.hpp b/lib/tdm_reaper.hpp
index 1f3788e..43a574c 100644
--- a/lib/tdm_reaper.hpp
+++ b/lib/tdm_reaper.hpp
@@ -180,76 +180,10 @@ public:
 
   // extract channel by id
   template<typename tdmtype>
-  std::vector<tdmtype> get_channel(std::string& id)
-  {
-    // check for existence of required channel id (=key)
-    if ( tdmchannels_.count(id) == 1 )
-    {
-      // // retrieve full channel info
-      // tdm_channel chn = tdmchannels_.at(id);
-      //
-      // // extract (first) "localcolumn" for channel
-      // if ( chn.local_columns_.size() != 1 )
-      // {
-      //   throw std::runtime_error(std::string("invalid local_columns_ of channel: ") + id);
-      // }
-      // localcolumn loccol = localcolumns_.at(chn.local_columns_[0]);
-      //
-      // if ( loccol.sequence_representation_ != "explicit" )
-      // {
-      //   throw std::runtime_error(std::string("unsupported sequence_representation: ")
-      //                             + loccol.sequence_representation_);
-      // }
-      //
-      // // use "values" id to map to external block
-      // block blk = tdx_blocks_.at(loccol.external_id_);
-      //
-      // // distinguish numeric datatypes
-      // switch ( blk.value_type_ )
-      // {
-      //   case "eInt16Usi" :
-      //     break;
-      //   case "eInt32Usi" :
-      //     break;
-      //   case "eUInt8Usi" :
-      //     break;
-      //   case "eUInt16Usi" :
-      //     break;
-      //   case "eUInt32Usi" :
-      //     break;
-      //   case "eFloat32Usi" :
-      //     // declare buffer covering the required range of "tdxbuffer_"
-      //     std::vector<unsigned char> blkF32( tdxbuffer_.begin()+blk.byte_offset_,
-      //                                         tdxbuffer_.begin()+blk.byte_offset_
-      //                                          + blk.length_*sizeof(eFloat32Usi) );
-      //     std::vector<eFloat32Usi> datvecF32(blk.length_);
-      //     this->convert_data_to_type<eFloat32Usi>(blkF32,datvecF32);
-      //     return datvecF32;
-      //     break;
-      //   case "eFloat64Usi" :
-      //     // declare buffer covering the required range of "tdxbuffer_"
-      //     std::vector<unsigned char> blkF64( tdxbuffer_.begin()+blk.byte_offset_,
-      //                                         tdxbuffer_.begin()+blk.byte_offset_
-      //                                          + blk.length_*sizeof(eFloat64Usi) );
-      //     std::vector<eFloat64Usi> datvecF64(blk.length_);
-      //     this->convert_data_to_type<eFloat64Usi>(blkF64,datvecF64);
-      //     return datvecF64;
-      //     break;
-      //   case "eStringUsi" :
-      //     throw std::runtime_error("datatype 'eStringUsi' is not supported");
-      //     break;
-      // }
-    }
-    else
-    {
-      throw std::invalid_argument(std::string("channel id does not exist: ") + id);
-    }
-
-    return std::vector<tdmtype>();
-  }
+  std::vector<tdmtype> get_channel(std::string& id);
 
   // (TODO introduce template T to reference specific datatype instead of double in general)
-  std::vector<double> get_channel(std::string &id);
+  // std::vector<double> get_channel(std::string &id);
 
   void print_channel(std::string &id, const char* filename);
 
diff --git a/src/main.cpp b/src/main.cpp
index 5b3225d..e4cc961 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -204,6 +204,9 @@ int main(int argc, char* argv[])
     std::string chid("usi14");
     std::vector<tdmdatatype> chdata = jack.get_channel<tdmdatatype>(chid);
 
+    std::cout<<"channel size: "<<chdata.size()<<"\n";
+    for ( tdmdatatype el: chdata ) std::cout<<el<<"\n";
+
     // std::vector<std::string> chgrids = jack.get_channelgroup_ids();
     // for ( auto el: chgrids ) std::cout<<el<<",";
     // std::cout<<"\n";