C++重载错误<<使用向量

Question

我试图通过使用向量和< <运算符来显示基本3乘3矩阵。问题是，当我尝试运行代码时，出现一个错误，指出在MatrixViaVector中没有成员命名大小。

在我的头文件我有：

#ifndef homework7_MatrixViaVector_h 
#define homework7_MatrixViaVector_h 

#include<iostream> 
#include<fstream> 
#include<string> 
#include <cstdlib> 
#include <vector> 

using namespace std; 
template <class T> 

class MatrixViaVector{ 

public: 
    MatrixViaVector(); 
    MatrixViaVector(int m,int n); 
    template <class H> 
    friend ostream& operator <<(ostream& outs, const MatrixViaVector<H> &obj); 
private: 
    int m,n; 
    vector<vector<T>> matrix; 
}; 

#endif 

而且在我的测试文件我有：

#include "MatrixViaVector.h" 

    template <class T> 
    MatrixViaVector<T>::MatrixViaVector(){ 

     //creates a 3 by 3 matrix with elements equal to 0 


     for (int i=0;i<3;i++){ 
      vector<int> row; 
      for (int j=0;j<3;j++) 
       row.push_back(0); 
      matrix.push_back(row); 
     } 
    } 

template <class T> 
MatrixViaVector<T>::MatrixViaVector(int m,int n)//creates a m by n matrix???? 
{ 
    //creates a matrix with dimensions m and n with elements equal to 0 

    for (int i=0;i<m;i++){ 
     vector<int> row; 
     for (int j=0;j<n;j++) 
      row.push_back(0); 
     matrix.push_back(row); 
    } 
} 

    template <class T> 
    ostream& operator <<(ostream& outs, const MatrixViaVector<T> & obj) 
    { 
     //obj shud have the vector and therefore I should be able to use its size 

     for (int i = 0; i < obj.size(); i++){ 
      for (int j = 0; j < obj.capacity(); j++) 
       outs << " "<< obj.matrix[i][j]; 
      outs<<endl; 
     } 
     outs<<endl; 
     return outs; 
    } 

    int main() 
    { 

    MatrixViaVector <int> A; 
    MatrixViaVector <int> Az(3,2);//created an object with dimensions 3by2???? 
    cout<<A<<endl; 
    cout<<Az<<endl;//this prints out a 3 by 3 matrix which i dont get???????? 
    } 

Answer 1

你MatrixViaVector<>不具有功能size()，但如果你打算使用矢量的大小做如下：

更改此片段：

for (int i = 0; i < obj.size(); i++){ 
     for (int j = 0; j < obj.capacity(); j++) 
      outs << " "<< obj.matrix[i][j]; 
     outs<<endl; 
    } 

要

for (std::vector<int>::size_type i = 0; i < obj.matrix.size(); i++){ 
     for (std::vector<int>::size_type j = 0; j < obj.matrix.size(); j++) 
      outs << " "<< obj.matrix[i][j]; 
     outs<<endl; 
    } 

std::vector::size()和std::vector::capacity() 2个不同的功能，请检查其差异。