C++ Output Iterator

• Output Iterator is an iterator used to modify the value in the container.
• Dereferencing an output iterator allows us to alter the value of the container.
• It does not allow us to read the value from the container.
• It is a one-way and write-only iterator.
• It can be incremented, but cannot be decremented.
• Operators that can be used for an output iterator are increment operator(++), decrement operator(–) and assignment operator(=).
• There are two main subclasses of an Output Iterator are:
  • insert iterator
  • ostream iterator

Insert Iterator

• An insert iterator is an iterator used to insert the element in a specified position.
• An assignment operator on the insert_iterator inserts the new element at the current position.

Syntax

Parameters

x: It is the container on which the new element is to be inserted.

it: It is an iterator object pointing to the position which is to be modified.

Let’s see a simple example:

Output:

Elements of v1 are : 1 2 3 3 4 5 6 7 4 5 

In the above example, insert_iterator is applied on the copy algorithm to insert the elements of the vector v2 into the vector v1 at a specified position pointed by it.

Ostream iterator

• An ostream iterators are the output iterators used to write to the output stream such as cout successively.
• An ostream iterator is created using a basic_ostream object.
• When an assigenment operator is used on the ostream iterator, it inserts a new element into the output stream.

Syntax

Member functions of Ostream Iterator class

Parameters

• T: It is the type of elements to be inserted into the container.
• charT: The type of elements that ostream can handle, for example, char ostream.
• traits: These are the character traits that the stream handles for the elements.

Let’s see a simple example:

Output:

10,20,30,40,50 

In the above example, out is an object of the ostream_iterator used to add the delimiter ‘,’ between the vector elements.

Let’s see another simple example of ostream iterator:

Output:

5,10,15, 

Features Of Output Iterator

• Equality/Inequality Operator: Output iterators cannot be compared either by using equality or inequality operator. Suppose X and Y are the two iterators:

• Dereferencing: An output iterator can be dereferenced as an lvalue.

• Incrementable: An output iterator can be incremented by using operator++() function.

Limitations Of Output Iterator

• Assigning but no accessing: We can assign an output iterator as an lvalue, but we cannot access them as an rvalue.

Suppose ‘A’ is an output iterator type and ‘x’ is a integer variable:

• It cannot be decremented: We can increment the output iterator by using operator++() function, but we cannot decrement the output iterator.

Suppose ‘A’ is an output iterator type:

• Multi-pass algorithm: An output iterator cannot be used as a multi-pass algorithm. Since an output iterator is unidirectional and can move only forward. Therefore, it cannot be used to move through the container multiple times

• Relational Operators: An output iterator cannot be compared by using any of the relational operators.

Suppose ‘A’ and ‘B’ are the two iterators:

• Arithmetic Operators: An output iterator cannot be used with the arithmetic operators. Therefore, we can say that the output iterator only moves forward in a sequential manner.

Suppose ‘A’ is an output iterator: