我很难在使用std :: for_each和其他算法的multimap,并想知道是否有人可以帮助我开发一个函数,可以传递适当的参数到“通用”函数。如何“调整”仿函数与map/multimap一起使用?
我的map/multimap的具体问题是它们的迭代器计算为std :: pair而不是包含的值(我的意思是mapped_type),我需要使用它。所以,我的问题是,是否有一种方法可以将适当的值传递给设计用于包含map/multimap类型之一的函数?
这里是我的示例代码:
// the key type for the multimap
typedef enum { ... } Module;
// my class as the mapped type for the multimap
struct Patch
{
void Apply(bool enable);
}
// I have some functors designed to work directly with Patch pointers
// because in other places I use set<Patch*> or other containers
struct ApplyOnCondtion: public unary_function<Patch*, void>
{
void operator() (Patch* patch)
{
if(some_condition) patch->Apply(enable_or_not);
}
}
// somewhere I have a collection of patches attributed to some module
multimap<Module, Patch*> patches;
// the problem is that using for_each with a map or a multimap results in
// a `pair<Module,Patch*>` as argument to the functor, not the Patch* as desired.
for_each(patches.begin(), patches.end(), ApplyOnCondition(...));
我想,也许bind1st或与mem_fun结合bind2nd可以解决这个问题,或者说我能想到的是其他的方式来创建一个新的仿函数,存储原来的函子,并通过这对的正确成员,但我没有设法得到任何好结果。任何有STL经验的人都可以提供一些建议吗?
EDIT 1
好吧,我可以不使用升压或额外的临时容器最好是:
#include <functional>
#include <utility>
using namespace std;
//////////////////////////////////////////////////////////////////////////
// any functor to be called must be derived from unary_function or
// have defined result_type and argument_type.
// template 'First' should be set to pair::first_type
template<typename First, typename Func>
class passSecond_t: public unary_function<
pair<First,typename Func::argument_type>,
typename Func::result_type>
{
Func* func;
public:
passSecond_t(Func &functor): func(&functor) {}
result_type operator()(argument_type value)
{
return (*func)(value.second);
}
};
// construction helper, unfortunately 'First' must be explicitly specified
template <typename First, typename Func>
passSecond_t<First, Func> passSecond(Func& functor)
{
return passSecond_t<First, Func> (functor);
}
// the following is a sample
#include <map>
#include <algorithm>
#include <iostream>
struct SampleClass
{
void execute(char* text)
{
cout << "this: " << this << ", text: " << text << endl;
}
};
struct SampleFunctor: public unary_function<SampleClass*,void>
{
char* text;
SampleFunctor(char* text_): text(text_) {}
result_type operator() (argument_type argu)
{
argu->execute(text);
}
};
void main()
{
map<int,SampleClass*> mymap;
SampleClass s1, s2;
mymap[0] = &s1;
mymap[1] = &s2;
SampleFunctor myfunctor("my text");
for_each(mymap.begin(), mymap.end(), passSecond<int>(myfunctor));
}