6.6. Mapping strings to Other Things
Problem
You have objects that you need to store in
memory, and you want to store them by their string
keys. You need to be able to add, delete, and retrieve items quickly
(with, at most, logarithmic complexity).
Solution
Use the standard container map
, declared in
<map>
, to map keys (string
s) to values (any type that obeys value semantics). Example 6-6 shows how.
Example 6-6. Creating a string map
#include <iostream> #include <map> #include <string> using namespace std; int main() { map<string, string> strMap; strMap["Monday"] = "Montag"; strMap["Tuesday"] = "Dienstag"; strMap["Wednesday"] = "Mittwoch"; strMap["Thursday"] = "Donnerstag"; strMap["Friday"] = "Freitag"; strMap["Saturday"] = "Samstag"; // strMap.insert(make_pair("Sunday", "Sonntag")); strMap.insert(pair<string, string>("Sunday", "Sonntag")); for (map<string, string>::iterator p = strMap.begin(); p != strMap.end(); ++p ) { cout << "English: " << p->first << ", German: " << p->second << endl; } cout << endl; strMap.erase(strMap.find("Tuesday")); for (map<string, string>::iterator p = strMap.begin(); p != strMap.end(); ++p ) { cout << "English: " << p->first << ", German: " << p->second << endl; } }
Discussion
A map
is an associative container that maps keys to
values, provides logarithmic complexity for inserting and finding, and constant time for
erasing single elements. It is common for developers to use a map to keep track of objects
by using a string
key. This is what Example 6-6 ...
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