public member function
<unordered_map>
| container iterator (1) |
const_iterator cbegin() const noexcept;
|
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| bucket iterator (2) |
const_local_iterator cbegin ( size_type n ) const; |
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Return const_iterator to beginning
Returns a const_iterator pointing to the first element in the unordered_multimap container (1) or in one of its buckets (2).
A const_iterator is an iterator that points to const content. This iterator can be increased and decreased (unless it is itself also const), just like the iterator returned by unordered_multimap::begin, but it cannot be used to modify the contents it points to.
Parameters
- n
- Bucket number. This shall be lower than bucket_count.
It is an optional parameter that changes the behavior of this member function: if set, the iterator retrieved points to the first element of a bucket, otherwise it points to the first element of the container.
Member type size_type is an unsigned integral type.
Return Value
A const_iterator to the first element in the container (1) or the bucket (2).
Both const_iterator and const_local_iterator are member types. In the unordered_multimap class template, these are forward iterator types.
const_local_iterator is an interator of the same category as const_iterator. Their value_type, difference_type, pointer and reference member types are also the same. But the iterators themselves are not necessarily of the same type.
Example
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// unordered_multimap::cbegin/cend example
#include <iostream>
#include <unordered_map>
int main ()
{
std::unordered_multimap<std::string,std::string> myumm = {
{"apple","red"},
{"apple","green"},
{"orange","orange"},
{"strawberry","red"}
};
std::cout << "myumm contains:";
for ( auto it = myumm.cbegin(); it != myumm.cend(); ++it )
std::cout << " " << it->first << ":" << it->second; // cannot modify *it
std::cout << std::endl;
std::cout << "myumm's buckets contain:\n";
for ( unsigned i = 0; i < myumm.bucket_count(); ++i) {
std::cout << "bucket #" << i << " contains:";
for ( auto local_it = myumm.cbegin(i); local_it!= myumm.cend(i); ++local_it )
std::cout << " " << local_it->first << ":" << local_it->second;
std::cout << std::endl;
}
return 0;
}
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Possible output:
myumm contains: apple:red apple:green orange:orange strawberry:red
myumm's buckets contain:
bucket #0 contains:
bucket #1 contains:
bucket #2 contains: apple:red apple:green
bucket #3 contains: orange:orange
bucket #4 contains: strawberry:red
|
Iterator validity
No changes.