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multimap lower_bound() function in C++ STL
• Last Updated : 09 Jun, 2020

The multimap::lower_bound(k) is a built-in function in C++ STL which returns an iterator pointing to the key in the container which is equivalent to k passed in the parameter. In case k is not present in the multimap container, the function returns an iterator pointing to the immediate next element which is just greater than k. If the key passed in the parameter exceeds the maximum key in the container, then the iterator returned points to key+1 and element = 0.

Syntax:

`multimap_name.lower_bound(key)`

Parameters: This function accepts a single mandatory parameter key which specifies the element whose lower_bound is to be returned.

Return Value: The function returns an iterator pointing to the key in the container which is equivalent to k passed in the parameter. In case k is not present in the multimap container, the function returns an iterator pointing to the immediate next element which is just greater than k. If the key passed in the parameter exceeds the maximum key in the container, then the iterator returned points to key+1 and element=0.

 `// C++ function for illustration ` `// multimap::lower_bound() function ` `#include ` `using` `namespace` `std; ` ` `  `int` `main() ` `{ ` ` `  `    ``// initialize container ` `    ``multimap<``int``, ``int``> mp; ` ` `  `    ``// insert elements in random order ` `    ``mp.insert({ 2, 30 }); ` `    ``mp.insert({ 1, 40 }); ` `    ``mp.insert({ 2, 60 }); ` `    ``mp.insert({ 2, 20 }); ` `    ``mp.insert({ 1, 50 }); ` `    ``mp.insert({ 4, 50 }); ` ` `  `    ``// when 2 is present ` `    ``auto` `it = mp.lower_bound(2); ` `    ``cout << ``"The lower bound of key 2 is "``; ` `    ``cout << (*it).first << ``" "` `         ``<< (*it).second << endl; ` ` `  `    ``// when 3 is not present ` `    ``it = mp.lower_bound(3); ` `    ``cout << ``"The lower bound of key 3 is "``; ` `    ``cout << (*it).first << ``" "` `         ``<< (*it).second << endl; ` ` `  `    ``// when 5 exceeds ` `    ``it = mp.lower_bound(5); ` `    ``cout << ``"The lower bound of key 5 is "``; ` `    ``cout << (*it).first << ``" "` `         ``<< (*it).second << endl; ` `    ``return` `0; ` `} `

Output:

```The lower bound of key 2 is 2 30
The lower bound of key 3 is 4 50
The lower bound of key 5 is 6 0
```

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