Question

我正在努力更好地熟悉C ++模板编程。为了实践，我决定实现一个优先级队列字典模板类，其中包含底层的priority_queue和unordered_map。但是，当我尝试在我的MBP上使用clang ++编译我的程序时，会打印出一些我不理解的错误消息。

我的代码在一个名为pqDictTotal.cpp的文件中

#include <queue>
#include <unordered_map>
#include <string>
#include <iostream>

template <typename P, typename V>
class PQDict {

private:

  std::priority_queue<P> *pq;
  std::unordered_map<P, V> *m;

public:

  int getSize() {

    return this->pq->size();
  }

  bool isEmpty() {

    return this->pq->empty();
  }

  V getMin() {

    P priority = this->pq->top();
    V value = this->m[priority];

    return value;
  }

  P getMinPriority() {

    return this->pq->top();
  }

  V removeMin() {

    P priority = this->pq->pop();
    V value = this->m[priority];
    this->m->erase(priority);

    return value;
  }

  void insert(P priority, V value) {

    this->pq->push(priority);
    this->m[priority] = value;
  }

  PQDict() {

    this->pq = new std::priority_queue<P>();
    this->m = new std::unordered_map<P, V>();
  }

  ~PQDict() {

    delete pq;
    delete m;
  }
};

int main() {

  PQDict<int, std::string> mypq;

  mypq.insert(23, "BDWF");
  mypq.insert(0, "ABC");
  mypq.insert(15, "SDFSDFL");
  mypq.insert(3, "GHF");
  mypq.insert(10, "LKSJDF");

  int minp;
  std::string mins;

  while (!mypq.isEmpty()) {

    minp = mypq.getMinPriority();
    mins = mypq.removeMin();

    std::cout << minp << ", " << mins << std::endl;
  }
}

使用

编译时

clang++ pqDictTotal.cpp

我得到了

pqDictTotal.cpp:51:23: error: no viable overloaded '='
    this->m[priority] = value;
    ~~~~~~~~~~~~~~~~~ ^ ~~~~~
pqDictTotal.cpp:71:8: note: in instantiation of member function 'PQDict<int,
      std::__1::basic_string<char> >::insert' requested here
  mypq.insert(23, "BDWF");
       ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/unordered_map:829:20: note: 
      candidate function not viable: no known conversion from
      'std::__1::basic_string<char>' to 'const std::__1::unordered_map<int,
      std::__1::basic_string<char>, std::__1::hash<int>,
      std::__1::equal_to<int>, std::__1::allocator<std::__1::pair<const int,
      std::__1::basic_string<char> > > >' for 1st argument
    unordered_map& operator=(const unordered_map& __u)
                   ^
pqDictTotal.cpp:41:7: error: cannot initialize a variable of type 'int' with an
      rvalue of type 'void'
    P priority = this->pq->pop();
      ^          ~~~~~~~~~~~~~~~
pqDictTotal.cpp:83:17: note: in instantiation of member function 'PQDict<int,
      std::__1::basic_string<char> >::removeMin' requested here
    mins = mypq.removeMin();
                ^
2 errors generated.

为什么我需要重载= for unordered_map？用'void'类型的rvalue'初始化'int'类型的变量是什么意思？

非常感谢任何帮助。

C ++基本模板类编译

0 个答案: