The C++ function std::unordered_map::cbegin() returns a constant iterator pointing to the first element in one of its buckets.
Following is the declaration for std::unordered_map::cbegin() function form std::unordered_map header.
const_local_iterator cbegin(size_type n) const;
n − Bucket number, which must be less than bucket_count.
Returns constant iterator.
Constant i.e. O(1)
The following example shows the usage of std::unordered_map::cbegin() function.
#include <iostream> #include <unordered_map> using namespace std; int main(void) { unordered_map<char, int> um = { {'a', 1}, {'b', 2}, {'c', 3}, {'d', 4}, {'e', 5} }; for (int i = 0; i < um.bucket_count(); ++i) { cout << "Bucket " << i << " contains:" << endl; for (auto it = um.cbegin(i); it != um.cend(i); ++it) cout << it->first << " = " << it->second << endl; } return 0; }
Let us compile and run the above program, this will produce the following result −
Bucket 0 contains: c = 3 Bucket 1 contains: d = 4 Bucket 2 contains: e = 5 Bucket 3 contains: Bucket 4 contains: Bucket 5 contains: Bucket 6 contains: Bucket 7 contains: Bucket 8 contains: Bucket 9 contains: a = 1 Bucket 10 contains: b = 2