Searching and Inserting in a map with 3 elements in C++

Question

I need to have a map like this :

typedef std::map<int, float , char> Maptype ;

What is the syntax to insert and searching elements of pair in this map.

Answer 1

A map can only map one key type to one data type. If the data contains 2 elements, use a struct or a std::pair.

typedef std::map<int, std::pair<float, char> > Maptype;
...
Maptype m;
m[123] = std::make_pair(0.5f, 'c');
...
std::pair<float, char> val = m[245];
std::cout << "float: " << val.first << ", char: " << val.second << std::endl;

Answer 2

You cannot have three elements. The STL map stores a key-value pair. You need to decide on what you are going to use as a key. Once done, you can probably nest the other two in a separate map and use it as:

typedef std::map<int, std::map<float, char> > MapType;

In order to insert in a map, use the operator[] or the insert member function. You can search for using the find member function.

MapType m;
// insert
m.insert(std::make_pair(4, std::make_pair(3.2, 'a')));
m[ -4 ] = make_pair(2.4, 'z');
// fnd
MapType::iterator i = m.find(-4);
if (i != m.end()) { // item exists ...
}

Additionally you can look at Boost.Tuple.

Answer 3

Use either

std::map<std::pair<int, float>, char>

or

std::map<int, std::pair<float, char> >

whichever is correct.