将 public 属性设置为私有
Set a public attribute as private
在
class vertex{
// ...
};
我正在尝试将此 public 属性设置为私有。
vector<edge> edges;
但是这里
void addedge(int from, int to, int length=-1) {
vertices[from].edges.push_back(edge(to, length));
}
这里
edge &e = vertices[u].edges[i];
我无法理解如何使用其他情况下的方法访问边缘。
完整代码:
#define MAX_VER 1000
#define INFINITE 9999
#include <vector>
#include <queue>
#include <iostream>
using namespace std;
class edge{
private:
int to;
int length;
public:
edge(int to, int length) : to(to), length(length) {}
int getTo(){return to;};
void setTo(int t){to=t;};
int getL(){return length;};
void setL(int l){length=l;};
};
class vertex{
private:
//vector<edge> edges;
int dis;
int prev;
public:
vector<edge> edges;
vector<edge> get_edges(){return edges;}
int getDis(){return dis;};
void setDis(int d){dis=d;};
int getPrev(){return prev;};
void setPrev(int p){prev=p;};
};
class graph{
private:
vertex vertices[MAX_VER];
public:
void reset() {
for (int i=0; i < MAX_VER; i++) {
vertices[i].get_edges().clear();
vertices[i].setDis(INFINITE);
vertices[i].setPrev(-1);
}
}
void addedge(int from, int to, int length=-1) {
vertices[from].edges.push_back(edge(to, length));
}
typedef pair<int, int> pp;
void dijkstra(int source) {
priority_queue<pp, vector<pp>, greater<pp> > q;
vertices[source].setDis(0);
q.push(make_pair(0, source));
while (!q.empty()) {
int u = q.top().second;
int dis = q.top().first;
q.pop();
if (dis > vertices[u].getDis())
continue;
for (int i = 0; i < vertices[u].get_edges().size(); i++) {
edge &e = vertices[u].edges[i];
if (dis + e.getL() < vertices[e.getTo()].getDis()) {
vertices[e.getTo()].setDis(dis + e.getL());
vertices[e.getTo()].setPrev(u);
q.push(make_pair(vertices[e.getTo()].getDis(), e.getTo()));
}
}
}
cout << "Distance from vertex 2 to 4 is: " << vertices[4].getDis() << endl;
}
};
int main() {
graph g;
g.reset();
g.addedge(0, 1, 5);
g.addedge(0, 2, 9);
g.addedge(0, 3, 4);
g.addedge(0, 4, 6);
g.addedge(1, 2, 2);
g.addedge(1, 3, 5);
g.addedge(1, 4, 7);
g.addedge(2, 3, 1);
g.addedge(2, 4, 8);
g.addedge(3, 4, 3);
g.dijkstra(2);
return 0;
}
edges
应该 是私有成员,可以通过 public get
函数访问。您已经定义了类似这样的内容 (get_edges()
),但它没有正确定义:
class vertex
{
//...
public:
vector<edge> edges;
vector<edge> get_edges(){return edges;}
//...
};
您 return 通过值成员,这意味着每次调用此函数时,都会创建 edges
的 新副本 并且该副本已 returned!
您应该 return 它作为参考并提供 const
和 non-const
对象的版本:
class vertex
{
//...
public:
vector<edge> edges;
vector<edge>& get_edges() { return edges; }
const vector<edge>& get_edges() const { return edges; }
//...
};
此外,edges
仅供 class graph
使用。所以可能这就足以宣布这两个 classes 之间的友谊?
将vertex
class改成这样:
class vertex
{
friend class graph; //declare friend
private:
int dis;
int prev;
vector<edge> edges; //make 'edges' private
public:
vector<edge>& get_edges() { return edges; }
const vector<edge>& get_edges() const { return edges; }
};
从现在开始,graph
class 将可以访问 vertex
class 的所有私有和受保护成员,因为它已被声明为它的好友。在简单的情况下,这是最快且侵入性较小的解决方案(但仅就需要编写的额外代码而言)。
在
class vertex{
// ...
};
我正在尝试将此 public 属性设置为私有。
vector<edge> edges;
但是这里
void addedge(int from, int to, int length=-1) {
vertices[from].edges.push_back(edge(to, length));
}
这里
edge &e = vertices[u].edges[i];
我无法理解如何使用其他情况下的方法访问边缘。
完整代码:
#define MAX_VER 1000
#define INFINITE 9999
#include <vector>
#include <queue>
#include <iostream>
using namespace std;
class edge{
private:
int to;
int length;
public:
edge(int to, int length) : to(to), length(length) {}
int getTo(){return to;};
void setTo(int t){to=t;};
int getL(){return length;};
void setL(int l){length=l;};
};
class vertex{
private:
//vector<edge> edges;
int dis;
int prev;
public:
vector<edge> edges;
vector<edge> get_edges(){return edges;}
int getDis(){return dis;};
void setDis(int d){dis=d;};
int getPrev(){return prev;};
void setPrev(int p){prev=p;};
};
class graph{
private:
vertex vertices[MAX_VER];
public:
void reset() {
for (int i=0; i < MAX_VER; i++) {
vertices[i].get_edges().clear();
vertices[i].setDis(INFINITE);
vertices[i].setPrev(-1);
}
}
void addedge(int from, int to, int length=-1) {
vertices[from].edges.push_back(edge(to, length));
}
typedef pair<int, int> pp;
void dijkstra(int source) {
priority_queue<pp, vector<pp>, greater<pp> > q;
vertices[source].setDis(0);
q.push(make_pair(0, source));
while (!q.empty()) {
int u = q.top().second;
int dis = q.top().first;
q.pop();
if (dis > vertices[u].getDis())
continue;
for (int i = 0; i < vertices[u].get_edges().size(); i++) {
edge &e = vertices[u].edges[i];
if (dis + e.getL() < vertices[e.getTo()].getDis()) {
vertices[e.getTo()].setDis(dis + e.getL());
vertices[e.getTo()].setPrev(u);
q.push(make_pair(vertices[e.getTo()].getDis(), e.getTo()));
}
}
}
cout << "Distance from vertex 2 to 4 is: " << vertices[4].getDis() << endl;
}
};
int main() {
graph g;
g.reset();
g.addedge(0, 1, 5);
g.addedge(0, 2, 9);
g.addedge(0, 3, 4);
g.addedge(0, 4, 6);
g.addedge(1, 2, 2);
g.addedge(1, 3, 5);
g.addedge(1, 4, 7);
g.addedge(2, 3, 1);
g.addedge(2, 4, 8);
g.addedge(3, 4, 3);
g.dijkstra(2);
return 0;
}
edges
应该 是私有成员,可以通过 public get
函数访问。您已经定义了类似这样的内容 (get_edges()
),但它没有正确定义:
class vertex
{
//...
public:
vector<edge> edges;
vector<edge> get_edges(){return edges;}
//...
};
您 return 通过值成员,这意味着每次调用此函数时,都会创建 edges
的 新副本 并且该副本已 returned!
您应该 return 它作为参考并提供 const
和 non-const
对象的版本:
class vertex
{
//...
public:
vector<edge> edges;
vector<edge>& get_edges() { return edges; }
const vector<edge>& get_edges() const { return edges; }
//...
};
此外,edges
仅供 class graph
使用。所以可能这就足以宣布这两个 classes 之间的友谊?
将vertex
class改成这样:
class vertex
{
friend class graph; //declare friend
private:
int dis;
int prev;
vector<edge> edges; //make 'edges' private
public:
vector<edge>& get_edges() { return edges; }
const vector<edge>& get_edges() const { return edges; }
};
从现在开始,graph
class 将可以访问 vertex
class 的所有私有和受保护成员,因为它已被声明为它的好友。在简单的情况下,这是最快且侵入性较小的解决方案(但仅就需要编写的额外代码而言)。