public member function
<map>

std::multimap::count

size_type count (const key_type& k) const;
Count elements with a specific key
Searches the container for elements with a key equivalent to k and returns the number of matches.

Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the keys are passed as arguments).

Parameters

k
Key to search for.
Member type key_type is the type of the element keys in the container, defined in map as an alias of its first template parameter (Key).

Return value

The number of elements in the container contains that have a key equivalent to k.

Member type size_type is an unsigned integral type.

Example

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// multimap::count
#include <iostream>
#include <map>

int main ()
{
  std::multimap<char,int> mymm;

  mymm.insert(std::make_pair('x',50));
  mymm.insert(std::make_pair('y',100));
  mymm.insert(std::make_pair('y',150));
  mymm.insert(std::make_pair('y',200));
  mymm.insert(std::make_pair('z',250));
  mymm.insert(std::make_pair('z',300));

  for (char c='x'; c<='z'; c++)
  {
    std::cout << "There are " << mymm.count(c) << " elements with key " << c << ":";
    std::multimap<char,int>::iterator it;
    for (it=mymm.equal_range(c).first; it!=mymm.equal_range(c).second; ++it)
      std::cout << ' ' << (*it).second;
    std::cout << '\n';
  }

  return 0;
}


Output:

There are 1 elements with key x: 50
There are 3 elements with key y: 100 150 200
There are 2 elements with key z: 250 300

Complexity

Logarithmic in size, plus linear in the number of matches.

Iterator validity

No changes.

Data races

The container is accessed.
No mapped values are accessed: concurrently accessing or modifying elements is safe.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.

See also

  • 997351548 2018-02-20
  • 903691547 2018-02-20
  • 9127171546 2018-02-20
  • 2234751545 2018-02-20
  • 1685381544 2018-02-20
  • 911091543 2018-02-20
  • 9281021542 2018-02-20
  • 632231541 2018-02-20
  • 9751491540 2018-02-20
  • 8333621539 2018-02-20
  • 995001538 2018-02-20
  • 6477441537 2018-02-20
  • 511981536 2018-02-19
  • 2072881535 2018-02-19
  • 6024461534 2018-02-19
  • 7594061533 2018-02-19
  • 9311341532 2018-02-19
  • 4928331531 2018-02-19
  • 38561530 2018-02-19
  • 7776611529 2018-02-19