How can I make a perl-like associative array in C++?, C++ FAQ

C++ FAQ / Section 34 / FAQ 34.2

Section 34:

34.1	Why should I use container classes rather than simple arrays?
34.2	How can I make a `perl`-like associative array in C++?
34.3	Is the storage for a `std::vector<T>` guaranteed to be contiguous?
34.4	How can I build a <favorite container> of objects of different types?
34.5	How can I insert/access/change elements from a linked list/hashtable/etc?
34.6	Can I have a container of smart pointers to my objects?

[34.2] How can I make a perl-like associative array in C++?

Use the standard class template std::map<Key,Val>:

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

int main()
{
  // age is a map from string to int
  std::map<std::string, int, std::less<std::string> >  age;

  age["Fred"] = 42;                     // Fred is 42 years old
  age["Barney"] = 37;                   // Barney is 37

  if (todayIsFredsBirthday())           // On Fred's birthday...
    ++ age["Fred"];                     // ...increment Fred's age

  std::cout << "Fred is " << age["Fred"] << " years old\n";
  ...
}

Nit: the order of elements in a std::map<Key,Val> are in the sort order based on the key, so from a strict standpoint, that is different from Perl's associative arrays which are unordered.