Modern C++ is amazingly powerful with many great features to help you write programs more easily with fewer errors. In C++, the Standard Template Library or STL has many algorithms for operations like searching, counting, and manipulation of ranges and their elements. In this Learn C++ post we show you a feature called std::map that you can use to pair elements.
What is std::map in Modern C++?
std::map is a sorted associative container in the C++ Standard Template Library (STL) that stores key-value pairs with unique keys matched to a value. Each member of the container has a unique key value and a mapped value. Two mapped values cannot have the same key values. When using std::map, key values are sorted by using the comparison function compare.
Here is the syntax for the std::map (Since C++17);
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namespace pmr { template< class Key, class T, class Compare = std::less<Key> > using map = std::map< Key, T, Compare, std::pmr::polymorphic_allocator<std::pair<const Key, T>> >; } |
How to use std::map in Modern C++? Example 1
Let’s assume we have string and integer values in our map. If you want to make string values key values that will be sorted, you can use std::map as shown below.
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std::map< std::string, int > mp; |
If you want, you can directly declare members of this map as shown below.
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std::map< std::string, int > mp{ {"Jim", 182}, {"David", 185}, {"Ian", 183} }; |
Or you can declare in the lines of program, here is a full example:
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#include <iostream> #include <map> #include <tchar.h> #include <string> int _tmain(int argc, _TCHAR* argv[]) { std::map< std::string, int > mp; mp["Jim"] = 182; mp["David"] = 185; mp["Ian"] = 183; for (const auto& [key, val] : mp) { std::cout << key << "," << val << " | "; } system("pause"); return 0; } |
and the output will be as follows,
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David,185 | Ian,183 | Jim,182 | Press any key to continue . . . |
How to use std::map in Modern C++? Example 2
Now, if you want to make integer values as key values that will be sorted, you can use std::map in the following way:
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std::map< int, std::string > mp; |
If you want, you can directly declare members of this map as shown below:
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std::map< std::string, int > mp{ {182, "Jim"}, {185, "David"}, {183, "Ian"} }; |
Or you can declare in the lines of program, here is a full example:
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#include <iostream> #include <map> #include <tchar.h> #include <string> int _tmain(int argc, _TCHAR* argv[]) { std::map<int, std::string > mp; mp[182] = "Jim"; mp[185] = "David"; mp[183] = "Ian"; for (const auto& [key, val] : mp) { std::cout << key << "," << val << " | "; } system("pause"); return 0; } |
and the output will be as follows,
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182,Jim | 183,Ian | 185,David | Press any key to continue . . . |
The std:map function is a very strong sorted associative container. It uses iterators like begin() and end(), it has modifiers like clear(), insert(), erase(), swap().
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