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map crbegin() and crend() function in C++ STL
In this article we will be discussing the working, syntax and examples of map::crbegin() and map::crend() functions in C++ STL.
What is a Map in C++ STL?
Maps are the associative container, which facilitates to store the elements formed by a combination of key value and mapped value in a specific order. In a map container the data is internally always sorted with the help of its associated keys. The values in the map container are accessed by its unique keys.
What is a map::cbegin()?
map::crbegin() function is an inbuilt function in C++ STL, which is defined in
Syntax
Map_name.crbegin();
Parameter
This function doesn’t accept any parameter.
Return value
This function returns the iterator which is pointing to the last element of the map container.
Example
Input
map<char, int> newmap; newmap[‘a’] = 1; newmap[‘b’] = 2; newmap[‘c’] = 3; newmap.crbegin();
Output
c:3
map::crbegin
Example
#include <bits/stdc++.h>
using namespace std;
int main() {
map<int, int> TP_Map;
TP_Map.insert({3, 50});
TP_Map.insert({2, 30});
TP_Map.insert({1, 10});
TP_Map.insert({4, 70});
//using map::crbegin to fetch first last element
auto temp = TP_Map.crbegin();
cout<<"First element is: "<<temp->first << " -> " << temp->second;
cout<<"\nTP Map is : \n";
cout << "MAP_KEY\tMAP_ELEMENT\n";
for (auto i = TP_Map.crbegin(); i!= TP_Map.crend(); i++) {
cout << i->first << "\t" << i->second << endl;
}
return 0;
}Output
First element is: 4 -> 70 TP Map is: MAP_KEY MAP_ELEMENT 4 70 3 50 2 30 1 10
What is map::crend()?
map::crend() function is an inbuilt function in C++ STL, which is defined in <map> header file. crend() implies constant reverse end iterator, means it is reverse of the cend which was constant end iterator, in other words the function crend() will return the iterator which is pointing to the position just before the first position of the map container associated with the function. This iterator can’t be used to modify the map. This can be just used to traverse the map container.
Syntax
newmap.crend();
Parameters
This function accepts no parameter.
Return value
It returns an iterator pointing to the preceding first element of the associated map container.
Example
Input
map<char, int> newmap; newmap[‘a’] = 1; newmap[‘b’] = 2; newmap[‘c’] = 3; newmap.crend();
Output
error
map::crend
Example
#include <bits/stdc++.h>
using namespace std;
int main() {
map<int, int> TP_Map;
TP_Map.insert({3, 50});
TP_Map.insert({2, 30});
TP_Map.insert({1, 10});
TP_Map.insert({4, 70});
cout<<"\nTP Map is : \n";
cout << "MAP_KEY\tMAP_ELEMENT\n";
for (auto i = TP_Map.crbegin(); i!= TP_Map.crend(); i++) {
cout << i->first << "\t" << i->second << endl;
}
return 0;
}Output
TP Map is: MAP_KEY MAP_ELEMENT 4 70 3 50 2 30 1 10
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