c++ "no appropriate default constructor available"错误使用模板类数据成员

Question

我做了一个模板类Grid(我在头文件中说T的默认值是float)，我引用了源文件的一部分:

#include"Grid.h"

template <class T>
Grid<T>::Grid(unsigned int rows=1, unsigned int columns=1)
:Rows(rows),Columns(columns)
{
reset();
}

template<class T>
Grid<T>::~Grid(){}

template <class T>
void Grid<T>::reset()
{
vector<T> vec(Rows * Columns,T());
matrix = vec;
}

其他成员函数可以读取/更改矩阵的值或对其进行计算。

网格.h:

template<typename T=float> class Grid{

public:
        Grid(unsigned int, unsigned int);
        ~Grid();
        T getValue(unsigned int, unsigned int);
        void setValue(unsigned int, unsigned int, T);
        void reset();
        void write();

private:
        unsigned int Rows;
        unsigned int Columns;
        vector<T> matrix;
};

我在互联网上发现，为了使用模板类，我需要 #include Grid.cpp 和 Grid.h，这样做我可以在我的 main() 中使用 clas Grid 及其成员函数。我还在 Grid.cpp 周围放置了一个预处理器包装器。

现在，当我尝试构建一个新类 PDEProblem 时，没有继承但使用 Grid 类型的成员，我得到错误:

    Error   2   error C2512: 'Grid<>' : no appropriate default constructor available      c:\users\...  15  

    Error   3   error C2512: 'Grid<T>' : no appropriate default constructor available   c:\users\...    15  
4   IntelliSense: no default constructor exists for class "Grid<float>" c:\Users\...    15

PDE问题.h:

#include"grid.h"
#include"grid.cpp"

class PDEProblem: Grid<>
{
public:
PDEProblem(unsigned int,unsigned int);
~PDEProblem();
//some more other data members

private:
Grid<char> gridFlags;
Grid<> grid;
unsigned int Rows;
unsigned int Columns;
void conPot(unsigned int, unsigned int);
void conFlag(unsigned int, unsigned int);
};

PDE问题.cpp:

#include"grid.h"
#include"grid.cpp"
#include "PDEProblem.h"

PDEProblem::PDEProblem(unsigned int rows=1,unsigned int columns=1)
    :Rows(rows), Columns(columns)
{
    conPot(rows, columns);
    conFlag(rows,columns);
}

PDEProblem::~PDEProblem(){}

void PDEProblem::conPot(unsigned int rows, unsigned int columns)
{
    grid=Grid<>(rows,columns);
}

void PDEProblem::conFlag(unsigned int rows, unsigned int columns)
 {gridFlags=Grid<char>(rows,columns);
    // some stuff with a few if and for loops which sets some elements of gridFlags to 1 and the others to 0
}

我该如何解决这个问题？在我看来，我对所有相关内容都有默认设置？谢谢

Answer 1

使用我的编译器 (Visual Studio 2010) 和您的代码，我可以通过将默认参数值从函数定义移至函数原型(prototype)来消除您的错误。具体来说:

网格.h

template<typename T=float> class Grid{

public:
    Grid(unsigned int rows = 1, unsigned int columns = 1);
...
};

网格.cpp

template <class T>
Grid<T>::Grid(unsigned int rows, unsigned int columns)
:Rows(rows),Columns(columns)
{
reset();
}