Question

what’s the alternative?

Should I write by myself?

Answer 1

There is the std::find() algorithm, which performs a linear search over an iterator range, e.g.,

std::vector<int> v;

// Finds the first element in the vector that has the value 42:
// If there is no such value, it == v.end()
std::vector<int>::const_iterator it = std::find(v.begin(), v.end(), 42);

If your vector is sorted, you can use std::binary_search() to test whether a value is present in the vector, and std::equal_range() to get begin and end iterators to the range of elements in the vector that have that value.