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Showing content from https://cplusplus.com/reference/map/map/find/ below:

public member function

<map>

std::map::find 
      iterator find (const key_type& k);const_iterator find (const key_type& k) const;

Get iterator to element

Searches the container for an element with a key equivalent to k and returns an iterator to it if found, otherwise it returns an iterator to map::end.

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

Another member function, map::count, can be used to just check whether a particular key exists.



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

Return value An iterator to the element, if an element with specified key is found, or map::end otherwise.

If the map object is const-qualified, the function returns a const_iterator. Otherwise, it returns an iterator.

Member types iterator and const_iterator are bidirectional iterator types pointing to elements (of type value_type).


Notice that value_type in map containers is an alias of pair<const key_type, mapped_type>.

Example 
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// map::find
#include <iostream>
#include <map>

int main ()
{
  std::map<char,int> mymap;
  std::map<char,int>::iterator it;

  mymap['a']=50;
  mymap['b']=100;
  mymap['c']=150;
  mymap['d']=200;

  it = mymap.find('b');
  if (it != mymap.end())
    mymap.erase (it);

  // print content:
  std::cout << "elements in mymap:" << '\n';
  std::cout << "a => " << mymap.find('a')->second << '\n';
  std::cout << "c => " << mymap.find('c')->second << '\n';
  std::cout << "d => " << mymap.find('d')->second << '\n';

  return 0;
}

Output: 
elements in mymap:
a => 50
c => 150
d => 200


Complexity Logarithmic in size.

Iterator validity No changes.

Data races The container is accessed (neither the const nor the non-const versions modify the container).
No mapped values are accessed: concurrently accessing or modifying elements is safe.

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

See also
map::operator[]
Access element (public member function)
map::count
Count elements with a specific key (public member function)
map::lower_bound
Return iterator to lower bound (public member function)
map::upper_bound
Return iterator to upper bound (public member function)

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