This tutorial will discuss about the set count() function in C++ stl.

**Table Of Contents**

In the C++ Standard Template Library (STL), the set is a container designed to store unique elements in a sorted sequence. The count() member function of the set container is utilized to determine the number of instances of a particular element present in the set.

## Syntax of set::count() Function

```
size_type count(const value_type& value) const;
```

**Parameters**:

– value: This is the value of the element that we want to count in the set. The type of this parameter is value_type, which corresponds to the data type of the elements stored in the set.

**Return Value**:

– Returns 1 if the element is found in the set.

– Returns 0 if the element is not found in the set.

The set class provides a function named count(), which accepts a value as an argument and returns the occurrence count of that value in the set. Since a set contains only unique elements, if the value exists in the set, the return value will always be 1.

This function can also serve as a means to check if an element exists in the set or not. If the return value is 1, it indicates the value exists in the set. Conversely, a return value of 0, means the element does not exist in the set.

### Frequently Asked:

- Different ways to Erase / Delete an element from a Set in C++
- Set cbegin() function in C++ STL
- C++: Convert Set to Vector
- Set size() function in C++ STL

## Example of set::count()

**Let’s see the complete example,**

#include <iostream> #include <set> int main() { std::set<int> numbers = {11, 22, 33, 44, 55}; std::cout << "Count of 22 in the set: " << numbers.count(20) << "n"; std::cout << "Count of 60 in the set: " << numbers.count(60) << "n"; // Get the occurrence count of value 22 in set // and also use that to check if element is in set or not if (numbers.count(22)) { std::cout << "Element 22 exists in set n"; } else { std::cout << "Element 22 does not exists in set n"; } return 0; }

**Output**

Count of 22 in the set: 0 Count of 60 in the set: 0 Element 22 exists in set

## Scenarios for Exceptions and Undefined Behavior with set::count()

**Thread Safety**: If the set is being accessed from multiple threads, and at least one of them modifies the set while another is performing a count() operation, it might lead to race conditions or undefined behavior. In such scenarios, it’s vital to use synchronization primitives or other concurrency control mechanisms.

**Summary**

Today, we learned about set count() function in C++ stl.