C++ Input Iterators

Introduction to C++ Input Iterators

In C++, iterators are an essential concept for working with containers and algorithms. They provide a way to access and manipulate elements within a container without exposing the underlying implementation details. Input iterators are a specific type of iterator that allows reading values from a range of elements.

Characteristics of Input Iterators

Input iterators have the following characteristics:

1. They support the increment operation (++it) to move to the next element.
2. They can be dereferenced to access the value of the current element (*it).
3. They can be compared for equality (it1 == it2) or inequality (it1 != it2).
4. They are read-only iterators, meaning that the elements they point to cannot be modified.

Examples of Input Iterators

Consider the following examples to understand how input iterators work:

Example 1: Reading Values from a Container

Suppose we have a vector of integers and we want to print its elements using input iterators:

“`cpp
#include
#include

int main() {
std::vector numbers = {1, 2, 3, 4, 5};

for (auto it = numbers.begin(); it != numbers.end(); ++it) {
std::cout << *it << ” “;
}

return 0;
}
“`

In this example, we use the `begin()` function to obtain an iterator pointing to the first element of the vector, and `end()` to obtain an iterator pointing to the position just after the last element. By iterating from the beginning to the end of the vector, we can access and print each element using the dereference operator `*`.

Example 2: Reading Values from Input Stream

Input iterators are also useful for reading values from input streams. Let’s see how we can use an input iterator to read integers from the standard input:

“`cpp
#include
#include
#include

int main() {
std::istream_iterator it(std::cin);
std::istream_iterator end;

std::vector numbers(it, end);

std::cout << “You entered: “;
std::copy(numbers.begin(), numbers.end(), std::ostream_iterator(std::cout, ” “));

return 0;
}
“`

In this example, we define an input iterator `it` using `std::istream_iterator`, which reads integers from the standard input (`std::cin`). We also define an `end` iterator to mark the end of input. By initializing a vector with the range defined by the iterators `it` and `end`, we can store the entered numbers. Finally, we use `std::copy` to print the numbers to the standard output.

Conclusion

Input iterators in C++ provide a convenient way to read values from containers or input streams. They allow us to iterate over a range of elements and perform operations without exposing the underlying implementation. Understanding how to use input iterators is crucial for working with various algorithms and data structures in C++.