Hi I'm having trouble getting to grips with how to organize my template classes in files. I've looked at C++ templates, undefined reference and am trying to use the tip given in http://www.parashift.com/c++-faq-lite/templates.html#faq-35.12 to separate my header and implementation files.
#include "Variables.h"
int main() {
Pressure<float,double> first(7.9,"atm");
return 0;
}
Variable is my top level class, I have removed some functions for brevity.
/*
* Variable_Parent.h
*
* Here an abstract base class from which variables can be derived is defined.
*
*/
#ifndef PARENT_VARIABLE_H_
#define PARENT_VARIABLE_H_
#include <string>
#include <map>
template <typename V,typename D> // To let different variables use different S.F.
struct Variable{
/*
* This structure is a abstract base class from which all dimensional variables
* are derived. Derived variables may be operated with and units will be largely
* automatically handled.
*/
protected:
//Functions
Variable(V v, std::string u, D conversions [], std::map<std::string,short> units);
~Variable();
//Variables
V value;
std::string unit;
std::map<std::string, unsigned short> * valid_units; //contains all units for which conversions have been defined.
D * conversion; //An n by n array for calculating conversions
public:
V get_value() const;
std::string get_unit() const;
void change_unit(std::string new_unit);
#endif /* PARENT_VARIABLE_H_ */
My implementation:
/*
* Header files
*/
#include "Variables_Parent.h"
#include <string>
#include <map>
#include <typeinfo>
template<typename V,typename D>
Variable<V,D>::Variable(V v, std::string u, D conversions [], std::map<std::string,short> units){
value = v;
unit = u;
conversion = conversions;
valid_units = &units;
}
template <typename V,typename D>
V Variable<V,D>::get_value() const{
return this.value;
}
template <typename V,typename D>
std::string Variable<V,D>::get_unit() const{
return unit;
}
template <typename V,typename D>
void Variable<V,D>::change_unit(std::string new_unit){
if (valid_units->find( new_unit ) == valid_units->end()){//Check the unit is defined
std::string message("%s is not a valid unit. /n", new_unit);
warning(message);
}
else{
int target = (*valid_units)[new_unit];
int original = (*valid_units)[unit];
int width = valid_units->size();
value*=conversion[ (original*width) + target];
unit=new_unit;
}
}
Now I want to be able to create specialized instances of this class which differ in where valid_units and conversion point to, I'm aware I could give this as an option in the constructor but as many of these may be created I wanted a simple constructor. So:
/*
* Variables.h
*
* Here all the variable classes are defined.
*
* Created on: Nov 16, 2011
* Author:
*/
#ifndef VARIABLES_H_
#define VARIABLES_H_
#include "Variables_Parent.h"
#include <string>
///////////////////////////////////////////////////////////////////////////////////////////////////////
/*
* Pressure
*/
template <typename V,typename D>
class Pressure : Variable<V,D> {
public:
Pressure(V v,std::string u);
~Pressure();
};
In the implementation file at the bottom I've commented out two template class declarations I was trying to use as suggested by the parashift FAQ, these lines give me the the console error:
Invoking: GCC C++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/Variables.d" -MT"src/Variables.d" -o"src/Variables.o" "../src/Variables.cpp"
../src/Variables.cpp: In constructor ‘Pressure<V, D>::Pressure(V, std::string) [with V = float, D = double, std::string = std::basic_string<char>]’:
../src/Variables.cpp:27:16: instantiated from here
../src/Variables.cpp:22:43: error: no matching function for call to ‘Variable<float, double>::Variable()’
../src/Variables_Parent.h:26:2: note: candidates are: Variable<V, D>::Variable(V, std::string, D*, std::map<std::basic_string<char>, short int>*) [with V = float, D = double, std::string = std::basic_string<char>]
../src/Variables_Parent.h:17:16: note: Variable<float, double>::Variable(const Variable<float, double>&)
../src/Variables.cpp:23:2: error: no matching function for call to ‘Variable<float, double>::Variable(float&, std::string&, double [3], const std::map<std::basic_string<char>, short unsigned int>&)’
../src/Variables_Parent.h:26:2: note: candidates are: Variable<V, D>::Variable(V, std::string, D*, std::map<std::basic_string<char>, short int>*) [with V = float, D = double, std::string = std::basic_string<char>]
../src/Variables_Parent.h:17:16: note: Variable<float, double>::Variable(const Variable<float, double>&)
make: *** [src/Variables.o] Error 1
\
/*
* Variables.c++
*
* Created on: Nov 18, 2011
* Author:
*/
#include "Variables.h"
#include <string>
#include <boost/assign.hpp>
///////////////////////////////////////////////////////////////////////////////////////////////////////
/*
* Pressure
*/
const static std::map<std::string, unsigned short> PRESSURE_UNITS =
boost::assign::map_list_of("kPa",0)("atm",1)("psi",2);// might want new
static double PRESSURE_CONVERSION[3][3]= {{1,0.009869232667,0.145037738},{101.325,1,14.6959488},{6.89475729,0.0680459639,1}};
template <typename V,typename D>
Pressure<V,D>::Pressure(V v, std::string u){
Variable<V,D>(v,u,PRESSURE_CONVERSION[0],PRESSURE_UNITS);
}
/*
template class Pressure<float, double>;
template class Variable<float, double>;
/*
When I do not include the declarations in main i get an error on trying to create first.
Multiple markers at this line
- undefined reference to Pressure<float, double>::~Pressure()'
- undefined reference toPressure::Pressure(float, std::basic_string, std::allocator
)'
Sorry about the length I wanted to make sure I included all relevant information given at this point I don't have a clue. Thanks in advance I hope I'm not going to have to move my implementation into my headers.
