模板矩阵标量乘C++

Question

当我尝试编译下面的代码，我得到一个错误说

错误1个错误LNK2019：无法解析的外部符号“类矩阵__cdecl的operator *（INT常量&，类矩阵& ）在函数_main C：\ Users \ pc \ Documents \ Visual Studio 2013 \ Projects \ Homework4 \ Homework4 \ main.obj中引用的“（?? D @ YA？AV？$ Matrix @ H $ 02 $ 01 @@ ABHAAV0 @@ Z）作业4

这个错误发生在矩阵上的标量乘，我不知道如何解决它。任何人都可以给我一个建议吗？

//Matrix.h 
#pragma once 
#include <iostream> 
#include <vector> 
using namespace std; 

template<class T, int m, int n> 
class Matrix 
{ 
vector<vector<T>> elements; 
int nrow; 
int ncol; 

public: 
Matrix(); 
~Matrix(); 
void print(); 
vector<T> row(int); 
vector<T> col(int); 

friend Matrix<T, m, n> operator+<>(const Matrix<T, m, n>&, const Matrix<T, m, n>&); 
friend Matrix<T, m, n> operator-<>(const Matrix<T, m, n>&, const Matrix<T, m, n>&); 
friend Matrix<T, m, n> operator*(const T&, Matrix<T, m, n>&); 

}; 

template<class T, int m, int n> 
Matrix<T, m, n>::Matrix() : nrow(m), ncol(n) 
{ 
for (int i = 0; i < nrow; i++){ 
    vector<T> row(ncol, i); 
    elements.push_back(row); 
} 
} 

template<class T,int m,int n> 
vector<T> Matrix<T, m, n>::row(int i) 
{ 
return elements[i]; 
} 

template<class T, int m, int n> 
vector<T> Matrix<T, m, n>::col(int j) 
{ 
vector<T> col; 
for (int i = 0; i < ncol; i++) 
{ 
    col.push_back(elements[i][j]); 
} 
return col; 
} 

template<class T, int m, int n> 
Matrix<T, m, n>::~Matrix(){} 

template<class T, int m, int n> 
void Matrix<T, m, n>::print() 
{ 
for (int i = 0; i < nrow; i++){ 
    for (int j = 0; j < ncol; j++) 
    { 
     cout << elements[i][j] << " "; 
    } 
    cout << endl; 
} 
} 

template<class T, int m, int n> 
Matrix<T, m, n> operator+(const Matrix<T, m, n>& m1, const Matrix<T, m, n>& m2){ 
Matrix<T, m, n> m3; 
int nrow = m1.nrow; 
int ncol = m1.ncol; 
for (int i = 0; i < nrow; ++i){ 
    for (int j = 0; j < ncol; ++j){ 
     m3.elements[i][j] = m1.elements[i][j] + m2.elements[i][j]; 
    } 
} 

return m3; 
} 

template<class T, int m, int n> 
Matrix<T, m, n> operator-(const Matrix<T, m, n>& m1, const Matrix<T, m, n>& m2){ 
Matrix<T, m, n> m3; 
int nrow = m1.nrow; 
int ncol = m1.ncol; 
for (int i = 0; i < nrow; ++i){ 
    for (int j = 0; j < ncol; ++j){ 
     m3.elements[i][j] = m1.elements[i][j] - m2.elements[i][j]; 
    } 
} 

return m3; 
} 


template<class T, int m, int n> 
Matrix<T, m, n> operator*(const T& c, const Matrix<T, m, n>& m1){ 
int nrow = m1.nrow; 
int ncol = m1.ncol; 
Matrix<T, m, n> m2; 
for (int i = 0; i < nrow; ++i){ 
    for (int j = 0; j < ncol; ++j){ 
     m2.elements[i][j] = c*m1.elements[i][j]; 
    } 
} 
return m2; 
} 

//main.cpp 
#include "Matrix.h" 
using namespace std; 

int main() 
{ 
Matrix<int, 3, 2> a; 
Matrix<int, 3, 2> b; 
Matrix<int, 3, 2> c; 
c = 2*b; 

c.print(); 
} 

我认为错误来自于类的身体的友元函数（操作*），但我不知道如何解决它......因为 一个发生

Answer 1

错误）operator*被声明为非模板（您应该使用<>） b）如果使用<>语法，则必须提供模板的声明。

修复 （添加Matrix类前）：

template<class T, int m, int n> 
class Matrix; 

template<class T, int m, int n> 
Matrix<T, m, n> operator*(T&, const Matrix<T, m, n>&); 

//class matrix definition here 

添加<>到operator*friend声明：

friend Matrix<T, m, n> operator*<>(T&, const Matrix<T, m, n>&);