代码：

template<typename T, typename U>

bool MapContainsKey(const map<T,U>& m,T key)

{

for (map<T, U>::iterator it = m.begin(); it != m.end(); ++it)//差点玩死我

{

if (it->first == key)

{

return true;

}

}

return false;

}

报错如下：=======================================================================

1>e:\program files\project\myregex20150310\test\source.cpp(38):

error C2440: 'initializing' : cannot convert from

'std::_Tree_const_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>'

to

'std::_Tree_iterator<std::_Tree_val<std::_Tree_simple_types<std::pair<const _Kty,_Ty>>>>'

1> with

1> [

1> _Kty=std::string

1> , _Ty=std::vector<int,std::allocator<int>>

1> ]

1> No constructor could take the source type, or constructor overload resolution was ambiguous

1> e:\program files\project\myregex20150310\test\source.cpp(70) : see reference to function template instantiation

'bool MapContainsKey<std::string,std::vector<int,std::allocator<_Ty>>>

(const std::map<std::string,std::vector<_Ty,std::allocator<_Ty>>,

std::less<_Kty>,

std::allocator<std::pair<const _Kty,std::vector<_Ty,std::allocator<_Ty>>>>> &,

T)'

being compiled

1> with

1> [

1> _Ty=int

1> , _Kty=std::string

1> , T=std::string

1> ]

===================================================================================

解决方案当然是把iterator改成const_iterator

===================================================================================