What is std istreambuf iterator in C++?

The std::istreambuf_iterator is a single-pass input iterator that reads characters one after the other from the std::basic_streambuf object for which it was constructed. The end-of-stream iterator is the default-constructed std::istreambuf_iterator. Upon reaching the end of the stream, a valid std::istreambuf_iterator equals the end-of-stream iterator. Dereferencing or incrementing it further triggers undefined behavior.

1. Containers: Containers Data structures are defined by these classes and store the information. The data can be stored in arrays, linked lists, or trees. The container types supported by the STL are vector, dequeue, list, forward list, set, multiset, map, and multimap.
2. Algorithms: We may also process data contained in containers using functions provided by the STL library. The file called algorithm header contains these functions.
3. Iterators: They act as a bridge between containers and algorithms, functioning as the shared interface for these classes. An Iterator is an object that may be used to iterate over the items of a container. Algorithms thus use iterators to swap out the containers.

The three parts are all designed to comply with data abstraction principles. As a result, a container is any object that functions like a container and contains data. In the same vein, an iterator is any function that iterates over the elements within a container.

As streams are also data containers by design, C++ gives us iterators to loop through the elements in any stream. We refer to these iterators as stream iterators. It is necessary to include the iterator header file for these iterators.

There are two types of stream iterators: input stream iterators and output stream iterators. These iterators belong to the class istream_iterator and function similarly to input iterators. When using an iterator, we are limited to accessing elements of a single type. When the stream reaches its end, or an input operation fails, istream_iterator acquires a unique state called the end-of-stream iterator. The default constructor returns an end-of-stream iterator.

Parameters:

CharType:

The type that istreambuf_iterator uses to denote its character type.

Traits:

The trait type represents character type representation for the istreambuf_iterator. The default value of this optional argument is char_traits<CharType>.

Remarks:

The istreambuf_iterator class must meet the specifications for an input iterator.

Following the construction or incrementation of an istreambuf_iterator object with a stored pointer that is not null, the object attempts to retrieve and store a CharType object from the corresponding input stream. Still, the extraction can wait until the object is copied or dereferenced. In the event that the extraction is unsuccessful, the object creates an end-of-sequence indicator by substituting a null pointer for the stored pointer.

Constructor:

Several constructor of the std::istreambuf_iterator are as follows:

istreambuf_iterator:

The istreambuf_iterator constructor initializes the istreambuf_iterator to read characters from the input stream.

Typedefs:

Char_type:

A type that indicates the character type of the ostreambuf_iterator.

Int_type:

An istreambuf_iterator can be given an integer type by using the int_type type.

istream_type:

A type that specifies the istream_iterator's stream type.

streambuf_type:

A type that specifies the istreambuf_iterator's stream type.

traits_type:

A type that supports the istream_iterator's character traits type.

Member function:

Equal:

It checks if two input stream buffer iterators are equivalent.

Operators:

Operator*:

The character that follows in the stream is returned by the dereferencing operator.

operator++:

This operator copies the object, increases it, and then returns the copy. Alternatively, it returns the character that comes next in the input stream.

Requirements:

Header: <iterator>

Namespace: standard

Iterator for istreambuf::Char_type:

A type that specifies the ostreambuf_iterator's character type.

typedef CharType char_type

Remarks:

The type and the template parameter CharType are interchangeable.

Example:

Let us take an example to illustrate the std::istresmbuf_iterator in C++.

#include <vector>

#include <sstream>

#include <iostream>

#include <iterator>

int main() {

   std::istringstream in("Hello, world");

   std::vector<char> k( (std::istreambuf_iterator<char>(in)),

                         std::istreambuf_iterator<char>() );

   std::cout << "k has " << k.size() << " bytes. ";

   k.push_back('\0');

   std::cout << "it holds \"" << &l[0] << "\"\n";

   std::istringstream s("abc");

   std::istreambuf_iterator<char> i2(s), i3(s);

   std::cout << "i2 returns " << *i2 << '\n'

             << "i3 returns " << *i3 << '\n';

   ++i2;

   std::cout << "after incrementing i2, but not i3\n"

             << "i2 returns " << *i2 << '\n'

             << "i3 returns " << *i3 << '\n';

   ++i3;

   std::cout << "after incrementing i3, but not i2\n"

             << "i2 returns " << *i2 << '\n'

             << "i3 returns " << *i3 << '\n';

}

Output:

k has 12 bytes. it holds "Hello, world"

i2 returns a

i3 returns a

after incrementing i2, but not i3

i2 returns b

i3 returns b

after incrementing i3, but not i2

i2 returns c

i3 returns c

Iterator for istreambuf::equal:

It examines whether two input stream buffer iterators are equivalent to one another.

equality of bool (const istreambuf_iterator<CharType, Traits>& right) const;

Parameters:

Right: The iterator whose equality needs to be verified.

Return Value:

The value returned is true if neither of the two streambed iterators is an end-of-stream iterator or false in the other case.

Remarks:

As all non-end-of-stream iterators are equivalent under the equal member function, istreambuf_iterators cannot be used to construct subranges.The meanings of the == and!= operators are the same.

Importance of Stream Iterators:

Stream iterators have the benefit of offering a consistent interface for accessing elements in file streams, external physical devices, and I/O streams.

1. The code that follows is essentially the same for all sorts of streams after an iterator to the appropriate stream has been obtained.
2. As a result, activities like reading from an input stream and reading from an external stream start to resemble one another.
3. By using stream iterators, we can access all of the strong STL algorithms, such as replace_if and for_each, which require an input range to function on. The clone() function is quite helpful. This function copies elements between containers.
4. Data can be moved from a stream to a container and vice versa by using the copy() function. Here are several sample programs that show how to use stream iterators.

Conclusion:

In conclusion, containers can be optimally traversed based on the iterator's category. Iterators improve maintainability and Code Reusability, making it simpler to develop generic code that functions with a range of containers.