在C ++迭代器问题中使用带有一对的映射作为键

Question

I have a pair and a map declared as such

typedef pair<string,string> Key;
typedef map< Key, double> Map;

i insert objects into them via a for loop as such

Key p (string1, string2 );
pair_map.insert(make_pair( p, double1 ) );

how can i find elements in the map? I am having trouble setting up the iterator with find.

Suppose I'm using it = pair_map.find(make_pair(string1,string2)) ;

I've tried declaring pair_map<Key, double>::iterator it; or map<Key, double>::iterator it; but neither are working for me. How can i fix this?

the errors i get are all long invalid cast errors because of the typedef's

Answer 1

Map::iterator it = pair_map.find(make_pair(string1, string2));

And of course you can use

auto it = ...;

or

decltype(pair_map.begin()) it = ...;

in C++11.

Answer 2

You need

Map::iterator it = ....

or, in C++11,

auto it = pair_map.find(make_pair(string1, string2));

Answer 3

pair_map is the name of a variable , not a type .

Map::iterator it = pair_map.find(make_pair(string1,string2));

(as juanchopanza says) will work, as will

std::map<Key, double>::iterator it = pair_map.find(make_pair(string1,string2));

or

auto it = pair_map.find(make_pair(string1,string2));

if you have C++11.

Answer 4

Don't use the variable name for the iterator type, but the type name, eg instead of :

pair_map<Key, double>::iterator it;

Use

Map::iterator it;

Or

map<Key, double>::iterator it;

Actually, you shouldn't typedef you map , since it's confusing. Just use the template everywhere.