c++双指针不知道转换

C++ double pointer not known conversion

本文关键字：转换 不知道 指针 c++      更新时间：2023-10-16

我真的被下面这些吓坏了:

template <class T> // int, float, double etc..
class Graph {
public:
  // Documentation, it has to be between [0..100]
  Graph(int size = 10, int density = 10, T range = 0):
    m_size(size),
    m_density(density),
    m_range(range) {
    generate();
  }
  ~Graph() {
     for (int i = 0; i < m_size; i++)
    delete[] m_graph[i];
      delete[] m_graph;
  }
  [..]
  static Graph<T>* custom(T** cgraph, int size, T range) {
    Graph<T> *graph = new Graph<T>(size, 10, range);
    for (int i = 0; i < size; i++)
      delete[] graph->m_graph[i];
    delete[] graph->m_graph;
    graph->m_graph = cgraph;
  }

private:
  T** m_graph;
  [ .. ]
};
int nodes[4][4] = {
  { 6, 5, 2, 5 },
  { 5, 6, 3, 3 },
  { 1, 3, 6, 1 },
  { 5, 3, 1, 6 }
};
int main() {
    Graph<int> *graph = Graph<int>::custom(nodes, 4, 5);
}

编译失败报告以下错误是什么?

   g++ graph.cpp -o test_graph 
graph.cpp: In function ‘int main()’:
graph.cpp:191:55: error: no matching function for call to ‘Graph<int>::custom(int [4][4], int, int)’
     Graph<int> *graph = Graph<int>::custom(nodes, 4, 5);
                                                       ^
graph.cpp:60:20: note: candidate: static Graph<T>* Graph<T>::custom(T**, int, T) [with T = int]
   static Graph<T>* custom(T** cgraph, int size, T range) {
                    ^
graph.cpp:60:20: note:   no known conversion for argument 1 from ‘int [4][4]’ to ‘int**’

看起来很好，怎么了

您需要通过指向int的指针数组来创建nodes。

int nodes_v[4][4] = {
  { 6, 5, 2, 5 },
  { 5, 6, 3, 3 },
  { 1, 3, 6, 1 },
  { 5, 3, 1, 6 }
};
int *nodes[4] = { nodes_v[0], nodes_v[1], nodes_v[2], nodes_v[3] };

您还需要向Graph变量添加一个额外的成员，以标记它是一个自定义图形，如果设置了，析构函数不应该删除内存。

最好给Graph一个私有构造函数，它传递custom标志，如果设置了，就不用费心分配内存。

  Graph(int size, int density, T range, bool custom):
    m_size(size),
    m_density(density),
    m_range(range),
    m_custom {
    }
  Graph(int size = 10, int density = 10, T range = 0):
    Graph(size, density, range, false) {
    generate();
    }
  static Graph<T>* custom(T** cgraph, int size, T range) {
        Graph<T> *graph = new Graph<T>(size, 10, range, true);
        graph->m_graph = cgraph;
  }

最后，需要处理复制构造函数和赋值操作符(从删除它们开始)。

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