C++传递引用

我最近(4天)开始学习C/C++ java背景下的C++。为了学习一门新的语言,我通常从重新实现不同的经典算法开始,尽可能地针对特定的语言。

我来看看这段代码,它是在无方向图中的DFS深度优先搜索。不过,从我读到的,最好通过C++中的引用传递参数。不幸的是,我不能完全理解引用的概念。每次我需要一个参考,我都会感到困惑,我会用指针来思考。在我当前的代码中,我使用passby值。

下面是代码(可能不是Cppthonic):

#include <algorithm>
#include <iostream>
#include <fstream>
#include <string>
#include <stack>
#include <vector>

using namespace std;

template <class T>
void utilShow(T elem);

template <class T>
void utilShow(T elem){
    cout << elem << " ";
}

vector< vector<short> > getMatrixFromFile(string fName);
void showMatrix(vector< vector<short> > mat);
vector<unsigned int> DFS(vector< vector<short> > mat);

/* Reads matrix from file (fName) */
vector< vector<short> > getMatrixFromFile(string fName)
{
    unsigned int mDim;
    ifstream in(fName.c_str());
    in >> mDim;
    vector< vector<short> > mat(mDim, vector<short>(mDim));
    for(int i = 0; i < mDim; ++i) {
        for(int j = 0; j < mDim; ++j) {
            in >> mat[i][j];
        }
    }
    return mat;
}

/* Output matrix to stdout */
void showMatrix(vector< vector<short> > mat){
    vector< vector<short> >::iterator row;
    for(row = mat.begin(); row < mat.end(); ++row){
        for_each((*row).begin(), (*row).end(), utilShow<short>);
        cout << endl;
    }
}

/* DFS */
vector<unsigned int> DFS(vector< vector<short> > mat){
    // Gives the order for DFS when visiting
    stack<unsigned int> nodeStack;
    // Tracks the visited nodes
    vector<bool> visited(mat.size(), false);
    vector<unsigned int> result;
    nodeStack.push(0);
    visited[0] = true;
    while(!nodeStack.empty()) {
        unsigned int cIdx = nodeStack.top();
        nodeStack.pop();
        result.push_back(cIdx);
        for(int i = 0; i < mat.size(); ++i) {
            if(1 == mat[cIdx][i] && !visited[i]) {
                nodeStack.push(i);
                visited[i] = true;
            }
        }
    }
    return result;
}

int main()
{
    vector< vector<short> > mat;
    mat = getMatrixFromFile("Ex04.in");
    vector<unsigned int> dfsResult = DFS(mat);

    cout << "Adjancency Matrix: " << endl;
    showMatrix(mat);

    cout << endl << "DFS: " << endl;
    for_each(dfsResult.begin(), dfsResult.end(), utilShow<unsigned int>);

    return (0);
}

你能给我一些关于如何使用引用的提示吗,通过引用这个代码?

对于C++中的二维数组,是否存在向量和类型**的标准替代方案?

以后编辑:

好的,我已经分析了你的答案(谢谢大家),并且我已经用更面向对象的方式重写了代码。同时我也明白了什么是参考资料,我们应该使用它。它有点类似于const指针,只是这种类型的指针可以包含NULL。

这是我的最新代码:

#include <algorithm>
#include <fstream>
#include <iostream>
#include <ostream>
#include <stack>
#include <string>
#include <vector>

using namespace std;

template <class T> void showUtil(T elem);

/**
* Wrapper around a graph
**/
template <class T>
class SGraph
{
private:
    size_t nodes;
    vector<T> pmatrix;
public:
    SGraph(): nodes(0), pmatrix(0) { }
    SGraph(size_t nodes): nodes(nodes), pmatrix(nodes * nodes) { }
    // Initialize graph from file name
    SGraph(string &file_name);
    void resize(size_t new_size);
    void print();
    void DFS(vector<size_t> &results, size_t start_node);
    // Used to retrieve indexes.
    T & operator()(size_t row, size_t col) {
        return pmatrix[row * nodes + col];
    }
};

template <class T>
SGraph<T>::SGraph(string &file_name)
{
    ifstream in(file_name.c_str());
    in >> nodes;
    pmatrix = vector<T>(nodes * nodes);
    for(int i = 0; i < nodes; ++i) {
        for(int j = 0; j < nodes; ++j) {
            in >> pmatrix[i*nodes+j];
        }
    }
}

template <class T>
void SGraph<T>::resize(size_t new_size)
{
    this->pmatrix.resize(new_size * new_size);
}

template <class T>
void SGraph<T>::print()
{
    for(int i = 0; i < nodes; ++i){
        cout << pmatrix[i];
        if(i % nodes == 0){
            cout << endl;
        }
    }
}

template <class T>
void SGraph<T>::DFS(vector<size_t> &results, size_t start_node)
{
    stack<size_t> nodeStack;
    vector<bool> visited(nodes * nodes, 0);
    nodeStack.push(start_node);
    visited[start_node] = true;
    while(!nodeStack.empty()){
        size_t cIdx = nodeStack.top();
        nodeStack.pop();
        results.push_back(cIdx);
        for(int i = 0; i < nodes; ++i){
            if(pmatrix[nodes*cIdx + i] && !visited[i]){
                nodeStack.push(i);
                visited[i] = 1;
            }
        }
    }
}

template <class T>
void showUtil(T elem){
    cout << elem << " ";
}

int main(int argc, char *argv[])
{
    string file_name = "Ex04.in";
    vector<size_t> dfs_results;

    SGraph<short> g(file_name);
    g.DFS(dfs_results, 0);

    for_each(dfs_results.begin(), dfs_results.end(), showUtil<size_t>);

    return (0);
}