我已经实现了这段代码,但编译失败(VC2008 Express Ed.):
现在所有代码都在这里。
#include <stdio.h>
#include <vector>
#include <string>
#include <hash_map>
using namespace std;
using namespace stdext;
typedef vector type_key;
int main(int argc, char* argv[])
{
type_key key;
hash_map<type_key, string> map_segment;
hash_map<type_key, string>::iterator iter_map_segment;
iter_map_segment = map_segment.find(key);
return 0;
}
使用 unordered_map 也会出现同样的错误。
但用 map 替换容器不会发生错误。
可以采取什么措施来纠正?
谢谢。
[已编辑]
错误信息:
------ Build started: Project: map_key_test, Configuration: Debug Win32 ------
Compiling...
map_key_test.cpp
c:\program files\microsoft visual studio 9.0\vc\include\xhash(75) : error C2440: 'type cast' : cannot convert from 'const type_key' to 'size_t'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
c:\program files\microsoft visual studio 9.0\vc\include\xhash(128) : see reference to function template instantiation 'size_t stdext::hash_value<_Kty>(const _Kty &)' being compiled
with
[
_Kty=type_key
]
c:\program files\microsoft visual studio 9.0\vc\include\xhash(127) : while compiling class template member function 'size_t stdext::hash_compare<_Kty,_Pr>::operator ()(const _Kty &) const'
with
[
_Kty=type_key,
_Pr=std::less<type_key>
]
c:\program files\microsoft visual studio 9.0\vc\include\hash_map(78) : see reference to class template instantiation 'stdext::hash_compare<_Kty,_Pr>' being compiled
with
[
_Kty=type_key,
_Pr=std::less<type_key>
]
c:\program files\microsoft visual studio 9.0\vc\include\xhash(191) : see reference to class template instantiation 'stdext::_Hmap_traits<_Kty,_Ty,_Tr,_Alloc,_Mfl>' being compiled
with
[
_Kty=type_key,
_Ty=std::string,
_Tr=stdext::hash_compare<type_key,std::less<type_key>>,
_Alloc=std::allocator<std::pair<const type_key,std::string>>,
_Mfl=false
]
c:\program files\microsoft visual studio 9.0\vc\include\hash_map(88) : see reference to class template instantiation 'stdext::_Hash<_Traits>' being compiled
with
[
_Traits=stdext::_Hmap_traits<type_key,std::string,stdext::hash_compare<type_key,std::less<type_key>>,std::allocator<std::pair<const type_key,std::string>>,false>
]
c:\users\salamon\documents\visual studio 2008\projects\map_key_test\map_key_test.cpp(17) : see reference to class template instantiation 'stdext::hash_map<_Kty,_Ty>' being compiled
with
[
_Kty=type_key,
_Ty=std::string
]
Build log was saved at "file://c:\Users\Salamon\Documents\Visual Studio 2008\Projects\map_key_test\Debug\BuildLog.htm"
map_key_test - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
[已编辑]
完整的解决方案:
#include <stdio.h>
#include <vector>
#include <string>
#include <hash_map>
using namespace std;
using namespace stdext;
class Vector : public vector<int>
{
public:
operator size_t() const { return (*this).size(); };
};
typedef Vector type_key;
struct less_vector
{
bool operator()(const Vector & x, const Vector & y) const
{
if ( x != y )
return true;
return false;
}
};
struct greater_vector
{
bool operator()(const Vector & x, const Vector & y) const
{
if ( x == y )
return true;
return false;
}
};
int main(int argc, char* argv[])
{
Vector key;
string str;
hash_map<Vector, string, hash_compare <Vector, less_vector > > map_segment;
hash_map<Vector, string, hash_compare <Vector, greater_vector > >::iterator iter_map_segment;
//
key.push_back(0);
key.push_back(1);
key.push_back(2);
str = "012";
map_segment [key] = str;
//
key.clear();
key.push_back(1);
key.push_back(0);
key.push_back(2);
str = "102";
map_segment [key] = str;
//
key.clear();
key.push_back(2);
key.push_back(1);
key.push_back(0);
str = "210";
map_segment [key] = str;
//
key.clear();
key.push_back(1);
key.push_back(0);
key.push_back(2);
iter_map_segment = map_segment.find(key);
return 0;
}
最佳答案
首先,请确保您所包含的 header 确实存在于您的安装中。
其次,hash_map在stdext
中命名空间,请确保通过将其显式指定为 stdext::hash_map
使该名称可见。 ,或通过 using
指令。
第三,代码中 hash_map 的模板参数在哪里?我只看到hash_map
而不是hash_map<vector<int>,string>
.
第四,我不确定 std::vector 是否可以像这样用作 HashMap 的哈希键。您需要为您的 key 定义一个哈希函数(通过实现 hash_compare
函数对象并将其传递给 hash_map
作为第三个模板参数)。无论如何,按值存储这些 vector 并不是一个好主意,相反,您可能应该考虑使用指向这些 vector 的指针作为键。
关于c++ - 使用 hash_map<vector<int>,string> 失败,为什么?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/873899/