C++ 初始化 map<string, vector<string> >
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initializing map<string, vector<string> >
提问by Anand
I am initializing map<string, vector<string> >as follows:
我初始化map<string, vector<string> >如下：
map <string, vector<string> > dict;
dict["USA"].push_back("NYC");
dict["USA"].push_back("LA");
dict["USA"].push_back("Chicago");
dict["USA"].push_back("Dallas");
dict["India"].push_back("Delhi");
dict["India"].push_back("Bombay");
dict["Australia"].push_back("Melbourne");
dict["Australia"].push_back("Sydney");
dict["Australia"].push_back("Adelaide");
I find this cumbersome. The same thing can be done in tclas follows which is cleaner:
我觉得这很麻烦。同样的事情可以做tcl如下，这更干净：
array set dict {
USA {NYC LA Chicago Dallas}
India {Delhi Bombay}
Australia {Melbourne Sydney Adelaide}
}
Is there a more cleaner way to initialize in C++? My compiler is gcc 3.4.6
有没有更简洁的初始化方式C++？我的编译器是gcc 3.4.6
采纳答案by haavee
If you're not afraid of using a bit of C-style macros and some helper constructs you might find this slightly less irritable; the initialization of the map is done in one line; you only need to fill in the data (which you must do anyway).
如果你不害怕使用一点 C 风格的宏和一些辅助结构，你可能会发现这有点不那么烦躁；地图的初始化在一行中完成；您只需要填写数据（无论如何您都必须这样做）。
#include <iostream>
#include <map>
#include <vector>
#include <string>
#include <utility>
using namespace std;
struct entry {
string key;
string* vals;
size_t nvals;
};
#define NVAL(x) (sizeof(x)/sizeof(x[0]))
int main( void ) {
// Create your data
string usa[] = {"NYC", "LA"};
string india[] = {"Delhi", "Mumbai"};
entry dd[] = {
{"USA", usa, NVAL(usa)},
{"India", india, NVAL(india)}
};
map<string, vector<string> > dict;
// initialize the map
for(unsigned int i=0; i<NVAL(dd); i++)
dict.insert( make_pair(dd[i].key, vector<string>(dd[i].vals, dd[i].vals+dd[i].nvals)) );
// Verify
for( map<string,vector<string> >::const_iterator ptr=dict.begin();
ptr!=dict.end(); ptr++) {
cout << ptr->first << ": ";
for( vector<string>::const_iterator eptr=ptr->second.begin();
eptr!=ptr->second.end(); eptr++)
cout << *eptr << " ";
cout << endl;
}
return 0;
}
回答by Kerrek SB
Initialization had many limitations in the old C++. Your code is in fact not initializing anything at all; it's just calling a lot of member functions on an already initialized object.
初始化在旧的 C++ 中有很多限制。你的代码实际上根本没有初始化任何东西；它只是在一个已经初始化的对象上调用了很多成员函数。
In the current C++ (C++11) you caninitialize your map properly:
在当前的 C++ (C++11) 中，您可以正确地初始化您的地图：
std::map<std::string, std::vector<std::string>> const dict {
{ "USA", { "NYC", "LA", "Chicago" } },
{ "India", { "Delhi", "Bombay" } }
};
回答by hatboyzero
If you're not opposed to using the Boost.Assign library and you are using C++ older than C++11, you can do it like this:
如果您不反对使用 Boost.Assign 库并且您使用的 C++ 早于 C++11，则可以这样做：
#include <boost/assign/list_of.hpp>
#include <boost/assign/std/vector.hpp>
#include <map>
#include <string>
#include <vector>
std::map<std::string, vector<std::string> > dict = boost::assign::map_list_of<std::string, std::vector<std::string> >
("USA", boost::assign::list_of<std::string>("NYC")("LA")("Chicago")("Dallas"))
("India", boost::assign::list_of<std::string>("Delhi")("Bombay"))
;
回答by Luchian Grigore
You could do this, if C++11 is not available:
如果 C++11 不可用，您可以这样做：
map <string, vector<string> > dict;
string usa[] = { "NYC" , "LA" , "Chicago" , "Dallas" };
dict["USA"] = std::vector<string>(usa,usa+4);
