How Can I Print out C++ Map Values?
I Have a Map Like This: Map myMap; and I've Inserted Some Data into My Map Using: myMap. Insert(Make_Pair(First_Name, Make_Pair(Middle_Name, Last_Name))); How...
I have a map like this:
map<string, pair<string,string> > myMap;
And I've inserted some data into my map using:
myMap.insert(make_pair(first_name, make_pair(middle_name, last_name)));
How can I now print out all the data in my map?
4 Answers
for(map<string, pair<string,string> >::const_iterator it = myMap.begin();
it != myMap.end(); ++it)
{
std::cout << it->first << " " << it->second.first << " " << it->second.second << "\n";
}
In C++11, you don't need to spell out map<string, pair<string,string> >::const_iterator. You can use auto
for(auto it = myMap.cbegin(); it != myMap.cend(); ++it)
{
std::cout << it->first << " " << it->second.first << " " << it->second.second << "\n";
}
Note the use of cbegin() and cend() functions.
Easier still, you can use the range-based for loop:
for(const auto& elem : myMap)
{
std::cout << elem.first << " " << elem.second.first << " " << elem.second.second << "\n";
}
If your compiler supports (at least part of) C++11 you could do something like:
for (auto& t : myMap)
std::cout << t.first << " "
<< t.second.first << " "
<< t.second.second << "\n";
For C++03 I'd use std::copy with an insertion operator instead:
typedef std::pair<string, std::pair<string, string> > T;
std::ostream &operator<<(std::ostream &os, T const &t) {
return os << t.first << " " << t.second.first << " " << t.second.second;
}
// ...
std:copy(myMap.begin(), myMap.end(), std::ostream_iterator<T>(std::cout, "\n"));
Since C++17 you can use range-based for loops together with structured bindings for iterating over your map. This improves readability, as you reduce the amount of needed first and second members in your code:
std::map<std::string, std::pair<std::string, std::string>> myMap;
myMap["x"] = { "a", "b" };
myMap["y"] = { "c", "d" };
for (const auto &[k, v] : myMap)
std::cout << "m[" << k << "] = (" << v.first << ", " << v.second << ") " << std::endl;
Output:
m[x] = (a, b)
m[y] = (c, d)
The easiest way is to declare an iterator first as
map<string ,string> :: iterator it;
and after that print it out by looping over the map using iterator from myMap.begin() to myMap.end() and print out key and value pairs in the map with it->first for key and it->second for value.
map<string ,string> :: iterator it;
for(it=myMap.begin();it !=myMap.end();++it)
{
std::cout << it->first << ' ' <<it->second;
}
Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.
