[英]C++ | overload operator << | std::map
我試圖在結構中重載 map 的運算符 <<,但出現編譯錯誤:
不存在從“std::_Rb_tree_const_iterator<std::pair<const int, int>>”到“std::_Rb_tree_iterator<std::pair<const int, int>>”的合適的用戶定義轉換
ostream& operator<<(ostream& os, const map<int, int>& neighbors)
{
string res;
map<int, int>::iterator it = neighbors.begin();
stringstream ss;
while (it != neighbors.end())
{
ss << "[id: " << it->first << " cost: " << it->second << "] ";
it++;
}
return os << ss;
}
如何正確獲取對 map 迭代器的引用? 我只能使用 C++ 98。
這是我的完整代碼
#pragma once
#include <map>
#include <string>
#include <sstream>
using namespace std;
struct LSA
{
int id;
int seqNum;
map <int, int> neighbors;
friend ostream& operator<<(ostream& os, const LSA& lsa);
friend ostream& operator<<(ostream& os, const map<int, int>& neighbors);
};
ostream& operator<<(ostream& os, const LSA& lsa)
{
return os << "[id: " << lsa.id << " seqNum: " << lsa.seqNum << " (" << lsa.neighbors.size() << " neighbors)";
}
ostream& operator<<(ostream& os, const map<int, int>& neighbors)
{
string res;
map<int, int>::iterator it = neighbors.begin();
stringstream ss;
while (it != neighbors.end())
{
ss << "[id: " << it->first << " cost: " << it->second << "] ";
it++;
}
return os << ss;
}
你有一個const
map,因此begin
返回一個const_iterator
,而不是一個iterator
。 沒有定義operator<<
接受stringstream
作為第二個參數,因此使用它的成員 function str
,如下
ostream& operator<<(ostream& os, const map<int, int>& neighbors)
{
string res;
map<int, int>::const_iterator it = neighbors.cbegin();
stringstream ss;
while (it != neighbors.end())
{
ss << "[id: " << it->first << " cost: " << it->second << "] ";
it++;
}
return os << ss.str();
}
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