Question

我正在调查地图如何处理自定义类型，我遇到了一些奇怪的行为。

我创建了一个自定义类型'ComplexType'，它有一个成员，一个指向int的指针。我首先使用此int的值进行比较，这给出了预期的行为。

#include <iostream>
#include <map>

struct ComplexType
{
    ComplexType(int i): index(new int(i)){
    };
    ComplexType(const ComplexType& cT): index(new int(*cT.index)){
    }
    ~ComplexType(){
        if(index){
            delete index;
        }
    }
    bool operator<(const ComplexType cT) const
    {
        return *index < *cT.index;
    }
    int* index;

};

int main(){
    int pi[] = {3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 8};
    std::map< ComplexType , int  > container;
    for(int i = 0; i < 12; ++i){
        container[ComplexType(i)] = pi[i];
    }
    std::cout << "Loop map, size: " << container.size() <<  std::endl;
    for(auto it = container.begin();it != container.end(); it++){
        std::cout << "Show index map, size: " << container.size() <<  std::endl;
        std::cout << *it->first.index << std::endl;
    }
    return 0;
}

输出：

Loop map, size: 12
Show index map, size: 12
0
Show index map, size: 12
1
Show index map, size: 12
2
Show index map, size: 12
3
Show index map, size: 12
4
Show index map, size: 12
5
Show index map, size: 12
6
Show index map, size: 12
7
Show index map, size: 12
8
Show index map, size: 12
9
Show index map, size: 12
10
Show index map, size: 12
11

现在我改变了比较函数以比较指针的地址。

#include <iostream>
#include <map>

struct ComplexType
{
    ComplexType(int i): index(new int(i)){
    };
    ComplexType(const ComplexType& cT): index(new int(*cT.index)){
    }
    ~ComplexType(){
        if(index){
            delete index;
        }
    }
    bool operator<(const ComplexType cT) const
    {
        return index < cT.index;
    }
    int* index;

};

int main(){
    int pi[] = {3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 8};
    std::map< ComplexType , int  > container;
    for(int i = 0; i < 12; ++i){
        container[ComplexType(i)] = pi[i];
    }
    std::cout << "Loop map, size: " << container.size() <<  std::endl;
    for(auto it = container.begin();it != container.end(); it++){
        std::cout << "Show index map, size: " << container.size() <<  std::endl;
        std::cout << *it->first.index << std::endl;
    }
    return 0;
}

我希望这会导致基于指针在堆上的地址的随机顺序。相反，我得到了以下内容：

Loop map, size: 12
Show index map, size: 12
1
Show index map, size: 12
0

我使用g ++（GCC）5.3.0编译

\randomness map>g++ -std=c++11 -o mapConstructionComplexType mapConstructionComplexType.cpp

\randomness map>g++ -std=c++11 -o mapConstructionComplexTypePointerCmp mapConstructionComplexTypePointerCmp.cpp

任何人都可以解释这种奇怪的行为吗？

std :: map operator＆lt;指针地址比较与指针值比较

0 个答案: