How to find out if an item is present in a std::vector?

As others have said, use the STL find or find_if functions. But if you are searching in very large vectors and this impacts performance, you may want to sort your vector and then use the binary_search, lower_bound, or upper_bound algorithms.

If your vector is not ordered, use the approach MSN suggested:

if(std::find(vector.begin(), vector.end(), item)!=vector.end()){ // Found the item } 

If your vector is ordered, use binary_search method Brian Neal suggested:

if(binary_search(vector.begin(), vector.end(), item)){ // Found the item } 

binary search yields O(log n) worst-case performance, which is way more efficient than the first approach. In order to use binary search, you may use qsort to sort the vector first to guarantee it is ordered.

Use find from the algorithm header of stl.I've illustrated its use with int type. You can use any type you like as long as you can compare for equality (overload == if you need to for your custom class).

#include <algorithm> #include <vector> using namespace std; int main() { typedef vector<int> IntContainer; typedef IntContainer::iterator IntIterator; IntContainer vw; //... // find 5 IntIterator i = find(vw.begin(), vw.end(), 5); if (i != vw.end()) { // found it } else { // doesn't exist } return 0; } 

In C++11 you can use any_of. For example if it is a vector<string> v; then:

if (any_of(v.begin(), v.end(), bind(equal_to<string>(), _1, item))) do_this(); else do_that(); 

Alternatively, use a lambda:

if (any_of(v.begin(), v.end(), [&](const std::string& elem) { return elem == item; })) do_this(); else do_that(); 

In C++23 we finally have a decent solution:

if (std::ranges::contains(vec, item)) do_this(); else do_that(); 

I use something like this...

#include <algorithm> template <typename T> const bool Contains( std::vector<T>& Vec, const T& Element ) { if (std::find(Vec.begin(), Vec.end(), Element) != Vec.end()) return true; return false; } if (Contains(vector,item)) blah else blah 

...as that way it's actually clear and readable. (Obviously you can reuse the template in multiple places).

From C++20, using ranges (#include <ranges>)

 //SAMPLE DATA std::vector<int> vecOfElements = { 2,4,6,8 }; //DO SOMETHING IF 8 IN VECTOR if (std::ranges::find(vecOfElements, 8) != vecOfElements.end()) { std::cout << "DO SOMETHING" << std::endl; } 

Here's a function that will work for any Container:

template <class Container> const bool contains(const Container& container, const typename Container::value_type& element) { return std::find(container.begin(), container.end(), element) != container.end(); } 

Note that you can get away with 1 template parameter because you can extract the value_type from the Container. You need the typename because Container::value_type is a dependent name.

Bear in mind that, if you're going to be doing a lot of lookups, there are STL containers that are better for that. I don't know what your application is, but associative containers like std::map may be worth considering.

std::vector is the container of choice unless you have a reason for another, and lookups by value can be such a reason.

With boost you can use any_of_equal:

#include <boost/algorithm/cxx11/any_of.hpp> bool item_present = boost::algorithm::any_of_equal(vector, element); 

Use the STL find function.

Keep in mind that there is also a find_if function, which you can use if your search is more complex, i.e. if you're not just looking for an element, but, for example, want see if there is an element that fulfills a certain condition, for example, a string that starts with "abc". (find_if would give you an iterator that points to the first such element).

You can try this code:

#include <algorithm> #include <vector> // You can use class, struct or primitive data type for Item struct Item { //Some fields }; typedef std::vector<Item> ItemVector; typedef ItemVector::iterator ItemIterator; //... ItemVector vtItem; //... (init data for vtItem) Item itemToFind; //... ItemIterator itemItr; itemItr = std::find(vtItem.begin(), vtItem.end(), itemToFind); if (itemItr != vtItem.end()) { // Item found // doThis() } else { // Item not found // doThat() } 

You can use the find function, found in the std namespace, ie std::find. You pass the std::find function the begin and end iterator from the vector you want to search, along with the element you're looking for and compare the resulting iterator to the end of the vector to see if they match or not.

std::find(vector.begin(), vector.end(), item) != vector.end() 

You're also able to dereference that iterator and use it as normal, like any other iterator.

You can use count too. It will return the number of items present in a vector.

int t=count(vec.begin(),vec.end(),item); 

I've personally used templates of late to handle multiple types of containers at once rather than deal only with vectors. I found a similar example online (can't remember where) so credit goes to whoever I've pilfered this from. This particular pattern seems to handle raw arrays as well.

template <typename Container, typename T = typename std::decay<decltype(*std::begin(std::declval<Container>()))>::type> bool contains(Container && c, T v) { return std::find(std::begin(c), std::end(c), v) != std::end(c); } 

template <typename T> bool IsInVector(const T & what, const std::vector<T> & vec) { return std::find(vec.begin(),vec.end(),what)!=vec.end(); } 

(C++17 and above):

can use std::search also

This is also useful for searching sequence of elements.

#include <algorithm> #include <iostream> #include <vector> template <typename Container> bool search_vector(const Container& vec, const Container& searchvec) { return std::search(vec.begin(), vec.end(), searchvec.begin(), searchvec.end()) != vec.end(); } int main() { std::vector<int> v = {2,4,6,8}; //THIS WORKS. SEARCHING ONLY ONE ELEMENT. std::vector<int> searchVector1 = {2}; if(search_vector(v,searchVector1)) std::cout<<"searchVector1 found"<<std::endl; else std::cout<<"searchVector1 not found"<<std::endl; //THIS WORKS, AS THE ELEMENTS ARE SEQUENTIAL. std::vector<int> searchVector2 = {6,8}; if(search_vector(v,searchVector2)) std::cout<<"searchVector2 found"<<std::endl; else std::cout<<"searchVector2 not found"<<std::endl; //THIS WILL NOT WORK, AS THE ELEMENTS ARE NOT SEQUENTIAL. std::vector<int> searchVector3 = {8,6}; if(search_vector(v,searchVector3)) std::cout<<"searchVector3 found"<<std::endl; else std::cout<<"searchVector3 not found"<<std::endl; } 

Also there is flexibility of passing some search algorithms. Refer here.

https://en.cppreference.com/w/cpp/algorithm/search

If you wanna find a string in a vector:

struct isEqual { isEqual(const std::string& s): m_s(s) {} bool operator()(OIDV* l) { return l->oid == m_s; } std::string m_s; }; struct OIDV { string oid; //else }; VecOidv::iterator itFind = find_if(vecOidv.begin(), vecOidv.end(), isEqual(szTmp)); 

How about this way?

 #include <iostream> #include <vector> #include <algorithm> int main() { std::vector<int> vec = {1, 2, 3, 4, 5}; // Find element 3 in the vector auto it = std::find(vec.begin(), vec.end(), 3); // Check if element is found if (it != vec.end()) { // Calculate index of the found element int index = std::distance(vec.begin(), it); std::cout << "Element 3 found at index: " << index << std::endl; } else { std::cout << "Element 3 not found" << std::endl; } return 0; } 

Another way to do it is using std::count.

Example code:

#include <algorithm> #include <vector> void run_vector_contains_example() { std::vector<int> vec = {1, 2, 3, 4, 5}; int item_to_find = 3; int count = std::count(vec.begin(), vec.end(), item_to_find); if (count > 0) { // item found in vector } else { // item not found in vector } } 

Admittedly, this method might be slower than std::find when dealing with large vectors.