C++ 在 std::vector<std::pair> 中查找
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find in std::vector<std::pair>
提问by Baz
I have a vector of pairs. The first in the pair is of type std::string and the second is of type Container.
我有一个成对的向量。该对中的第一个是 std::string 类型，第二个是 Container 类型。
What convenient functionality exists in std or boost so that I can return a Container given the string value as key?
std 或 boost 中存在哪些方便的功能，以便我可以以字符串值作为键返回一个容器？
UPDATE
更新
It has been commented that I could use a std::map instead, but I actually need to preserve the order of my items, in the order that I push them to the vector.
有人评论说我可以使用 std::map 代替，但我实际上需要保留我的项目的顺序，按照我将它们推送到向量的顺序。
回答by Andy Prowl
A possible solution:
一个可能的解决方案：
struct comp
{
comp(std::string const& s) : _s(s) { }
bool operator () (std::pair<std::string, Container> const& p)
{
return (p.first == _s);
}
std::string _s;
};
// ...
typedef std::vector<std::pair<std::string, Container> > my_vector;
my_vector v;
// ...
my_vector::iterator i = std::find_if(v.begin(), v.end(), comp("World"));
if (i != v.end())
{
Container& c = i->second;
}
// ...
Here is a complete example:
这是一个完整的例子：
#include <vector>
#include <utility>
#include <string>
#include <algorithm>
struct Container
{
Container(int c) : _c(c) { }
int _c;
};
struct comp
{
comp(std::string const& s) : _s(s) { }
bool operator () (std::pair<std::string, Container> const& p)
{
return (p.first == _s);
}
std::string _s;
};
#include <iostream>
int main()
{
typedef std::vector<std::pair<std::string, Container> > my_vector;
my_vector v;
v.push_back(std::make_pair("Hello", Container(42)));
v.push_back(std::make_pair("World", Container(1729)));
my_vector::iterator i = std::find_if(v.begin(), v.end(), comp("World"));
if (i != v.end())
{
Container& c = i->second;
std::cout << c._c; // <== Prints 1729
}
}
And here is a live example.
这是一个活生生的例子。
回答by Paul Fultz II
Using Boost.Rangeand Boost.Bind, you can do this:
使用Boost.Range和Boost.Bind，你可以这样做：
struct predicate
{
template<class Key, class Pair>
bool operator()(const Key& k, const Pair& p) const
{
return p.first == k;
}
};
// Your vector of pairs
std::vector<std::pair<std:string, Container> v = ...;
// The key you would like to search for
std::string key = ...;
Container& c = boost::find_if(v, boost::bind(predicate(), key, _1))->second;
回答by Charles L Wilcox
There is a simple solution: use std::copyand std::inserter:
有一个简单的解决方案：使用std::copy和std::inserter：
#include <algorithm>
#include <map>
#include <string>
#include <utility> // pair
#include <vector>
void function()
{
typedef int Data;
typedef std::pair< std::string, Data > String_Data_Pair;
typedef std::vector< String_Data_Pair > String_Data_Pair_Sequence;
typedef std::map< std::string, Data > String_To_Data_Map;
String_Data_Pair_Sequence string_data_pairs;
/* fill 'string_data_pairs' here */
String_To_Data_Map string_to_data_map;
std::copy( string_data_pairs.begin(),
string_data_pairs.end(),
std::inserter( string_to_data_map,
string_to_data_map.begin() /* superfluous, but required */ ) );
}
回答by Stefan Matta
class SomeClass{
int num;
public:
SomeClass();
void setNumber(int n) const { num = n;}
};
vector<pair<SomeClass,string> > vectr;
for(unsigned int i = 0; i < vectr.size(); i++)
if(vectr[i].second == "key")
vectr[i].first.setNumber(50);
Worked for me!
为我工作！
