The unordered_map::begin() is a built-in function in C++ STL which returns an iterator pointing to the first element in the unordered_map container or in any of its bucket.
- Syntax for first element in unordered_map container:
unordered_map.begin()
Parameters: This function does not accepts any parameters.
Return Value: The function returns an iterator pointing to the first element in the unordered_map container.
Note: In an unordered map, there is no specific element which is considered as the first element.
Below program illustrate the above function.
// CPP program to demonstrate the // unordered_map::begin() function // when first element of the container // is to be returned as iterator #include <bits/stdc++.h> using namespace std;
int main()
{ // Declaration
unordered_map<std::string, std::string> mymap;
// Initialisation
mymap = { { "Australia" , "Canberra" },
{ "U.S." , "Washington" },
{ "France" , "Paris" } };
// Iterator pointing to the first element
// in the unordered map
auto it = mymap.begin();
// Prints the elements of the first element in map
cout << it->first << " " << it->second;
return 0;
} |
France Paris
- Syntax for first element in unordered_map bucket:
unordered_map.begin( n )
Parameters: The function accepts one mandatory parameter n which specifies the bucket number whose first element’s iterator is to be returned.
Return Value: The function returns an iterator pointing to the first element in the n-th bucket.
Below program illustrate the above function.
// CPP program to demonstrate the // unordered_map::begin() function // when first element of n-th container // is to be returned as iterator #include <bits/stdc++.h> using namespace std;
int main()
{ // Declaration
unordered_map<std::string, std::string> mymap;
// Initialisation
mymap = { { "Australia" , "Canberra" },
{ "U.S." , "Washington" }, { "France" , "Paris" } };
// Iterator pointing to the first element
// in the n-th bucket
auto it = mymap.begin(0);
// Prints the elements of the n-th bucket
cout << it->first << " " << it->second;
return 0;
} |
U.S. Washington