Arrays using STD containers

grob115 · 02-07-2012, 11:41 AM

Hi, majority of examples of the containers such as std::map are based on a key value pair. Say for example if I want to have something similar to an array, how do I do this? An example would be like the following.

Key 1, Value 1a, Value 1b
Key 2, Value 2a, Value 2b
Key 3, Value 3a, Value 3c

An example application would be using the keys to store product codes, value <x>a to store the price, and value <x>b to store availability (true or false as a boolean). How do I declare the variable in this case?

dwhitney67 · 02-07-2012, 12:27 PM

Quote:

Originally Posted by grob115

Hi, majority of examples of the containers such as std::map are based on a key value pair. Say for example if I want to have something similar to an array, how do I do this? An example would be like the following.

Key 1, Value 1a, Value 1b
Key 2, Value 2a, Value 2b
Key 3, Value 3a, Value 3c

An example application would be using the keys to store product codes, value <x>a to store the price, and value <x>b to store availability (true or false as a boolean). How do I declare the variable in this case?

Define a structure to contain the values; then use this type as the value-type for the std::map. Here's a simple example:

Code:

#include <map>
#include <string>
#include <iostream>
#include <algorithm>

struct Values
{
    Values(const int v1 = 0, const int v2 = 0) : val1(v1), val2(v2) {}

    int val1;
    int val2;

    friend std::ostream& operator<<(std::ostream& os, const Values& v)
    {
        os << v.val1 << ", " << v.val2;
        return os;
    }
};

void displayEntry(const std::pair<int, Values>& entry)
{
   std::cout << "Entry " << entry.first << " has these values: " << entry.second << std::endl;
}

int main()
{
    typedef std::map<int, Values> MyMap;

    MyMap mm;

    mm[20] = Values(20, 200);   // note: copy-constructor called here!  This may not be desirable.
    mm[10] = Values(10, 100);   // same here
    mm[30] = Values(30, 300);   // same here

   std::for_each(mm.begin(), mm.end(), displayEntry);
}