为什么hash_map.find参数必须是int

[huis]

stdext::hash_map<_bstr_t,IndicationParam> indParams;
indParams.find(_bstr_t("aaa"));

编译时提示错误
错误 3 error C2440: “类型转换”: 无法从“const _bstr_t”转换为“size_t” d:\program files\microsoft visual studio 9.0\vc\include\xhash 71 GpTask

把_bstr_t改成int类型就可以!

[wangdeqie]

[Quote=引用 8 楼 huis 的回复:]
还是不行!
[/Quote]

//int是内建类型，是内部定义好的适用类型，所以可以直接用，而自定义类型包括string，都需要自己重写哈希函数和比较函数

//怎么会不行呢，我都运行出结果了，下面的运行结果：

find sucessful!
请按任意键继续. . .

//把下面的代码粘贴到 DEV C++下的一个新工程里：

#include <cstdlib>
#include <iostream>
#include <string>
#include <hash_map.h>

using namespace std;

struct bstr_t_hash;
struct equal_A;

class bstr_t //类
{
      friend struct bstr_t_hash;
      friend struct equal_A;
public:
      bstr_t(string s):str(s){}
private:
      string str;              
};

struct bstr_t_hash //哈希函数
{
        size_t operator()(const bstr_t& s) const
        {
                unsigned long __h = 0;
                for (size_t i = 0 ; i < s.str.size() ; i ++)
                __h = 5*__h + s.str[i];
                return size_t(__h);
        }
};
struct equal_A //比较函数
{
        bool operator()(const class bstr_t & a1, const class bstr_t & a2)const{
                return  a1.str == a2.str;
        }
};

int main(int argc, char *argv[])
{
    hash_map <bstr_t,int,bstr_t_hash,equal_A> indParams; 
    indParams.insert(hash_map <bstr_t,int,bstr_t_hash,equal_A>::value_type(bstr_t("aaa"),1));
    if(indParams.find(bstr_t("aaa"))!=indParams.end())
        cout<<"find sucessful!"<<endl; 

    system("PAUSE");
    return EXIT_SUCCESS;
}

[backway]

UP

[帅得不敢出门]

10楼的方法 gcc编译通过

[yeah920]

友情up一下.

[wangdeqie]

自定义类型，得重写哈希函数和比较函数

[lyle3]

学习

[wangdeqie]

//比如这么写：运行环境 DEV C++
#include <cstdlib>
#include <iostream>
#include <hash_map.h>

using namespace std;

struct bstr_t_hash;

class bstr_t
{
      friend struct bstr_t_hash;
public:
      bstr_t(string s):str(s){}
private:
      string str;              
};

struct bstr_t_hash{
        size_t operator()(const bstr_t& s) const
        {
                unsigned long __h = 0;
                for (size_t i = 0 ; i < s.str.size() ; i ++)
                __h = 5*__h + s.str[i];
                return size_t(__h);
        }
};

int main(int argc, char *argv[])
{
    hash_map <string,int,bstr_t_hash> indParams; 
    indParams.find(("aaa")); 

    system("PAUSE");
    return EXIT_SUCCESS;
}

[wangdeqie]

//看这个吧，偶又改了下
#include <cstdlib>
#include <iostream>
#include <string>
#include <hash_map.h>

using namespace std;

struct bstr_t_hash;
struct equal_A;

class bstr_t
{
      friend struct bstr_t_hash;
      friend struct equal_A;
public:
      bstr_t(string s):str(s){}
private:
      string str;              
};

struct bstr_t_hash{
        size_t operator()(const bstr_t& s) const
        {
                unsigned long __h = 0;
                for (size_t i = 0 ; i < s.str.size() ; i ++)
                __h = 5*__h + s.str[i];
                return size_t(__h);
        }
};
struct equal_A{
        bool operator()(const class bstr_t & a1, const class bstr_t & a2)const{
                return  a1.str == a2.str;
        }
};

int main(int argc, char *argv[])
{
    hash_map <bstr_t,int,bstr_t_hash,equal_A> indParams; 
    indParams.find(bstr_t("aaa")); 

    system("PAUSE");
    return EXIT_SUCCESS;
}

[e_sharp]

需要自己写hash函数，针对 _bstr_t 的特化版本

template<>
struct hash<_bstr_t> {...};

[太乙]

~~~up~~~

[huis]

还是不行!

[sunxuehui]

http://www.cnblogs.com/huis/archive/2008/11/04/1326107.html