Question

您好我无法掌握如何在文件中组织模板类。我看过C++ templates, undefined reference 我正在尝试使用http://www.parashift.com/c++-faq-lite/templates.html#faq-35.12中给出的提示来分隔我的标题和实现文件。

    #include "Variables.h"

    int main() {
Pressure<float,double> first(7.9,"atm");
return 0;
    }

变量是我的顶级类，为简洁起见，我删除了一些函数。

 /*
 * 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_ */

我的实施：

    /*
     * 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;
    }
}

现在我希望能够创建这个类的专用实例，它们在valid_units和转换指向的位置有所不同，我知道我可以在构造函数中将它作为一个选项，但是我可能会创建其中的许多一个简单的构造函数。所以：

/*
 * 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();
};

在底部的实现文件中，我已经注释掉了我试图使用的两个模板类声明，如parashift FAQ所示，这些行给了我控制台错误：

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>;
/*

当我没有在main中包含声明时，我首先尝试创建时出错。此行有多个标记 - 对Pressure<float, double>::~Pressure()' - undefined reference to压力::压力（float，std :: basic_string，std :: allocator

的未定义引用

）'

对于我想确保我包含此时提供的所有相关信息的长度感到抱歉我没有任何线索。在此先感谢，我希望我不必将我的实现移到我的标题中。

Answer 1

使用模板时，实现应该在定义接口的转换单元（最常见的是相同的头文件）中。有解决方法，但事实总是存在。

Answer 2

您可能需要仔细研究一下：http://www.amath.unc.edu/sysadmin/DOC4.0/c-plusplus/c%2B%2B_ug/Templates.new.doc.html从那篇文章

开始

由于标题和模板源文件的分离，您必须非常小心文件构造，放置和命名。您可能还需要向编译器明确标识源文件的位置。

模板超过多个文件困难

2 个答案: