Analysis of STL source code--classification of each container iterator

The five types of iterators are as follows:

1. Input iterator: read-only, one pass
The predefined implementations for input iterators are only Istream_iterator and istreambuf_iterator, which are used to read from an input stream istream. An input iterator can only parse each element of its choice once, and they can only move forward. A specialized constructor defines the value beyond the end. Always, an input iterator can parse the results of a read operation (once for each value) and move forward.
2, Output iterator: Write only, one pass
This complements the input iterator, but is a write operation rather than a read operation. The predefined implementations for output iterators are only Ostream_iterator and ostreambuf_iterator, which are used to ostream write data to an output stream, and there is a generally less-used raw_storage_iterator. They can only parse once for each value written, and move forward only. For an output iterator, the concept of ending with a value beyond the end is not used. In summary, an output iterator can parse the value of a write operation (only once for each value), and then move forward.
3. Forward iterators: Read/write multiple times
The forward iterator contains the functions of both the input and output iterators, plus the position specified by an iterator can be parsed multiple times, so that a value can be read/written multiple times. As the name implies, forward iterators can only move forwards. There are no predefined iterators for the forward iterator.
4, bidirectional iterator: operator--
Bidirectional iterators have all the functions of a forward iterator. It can also use the operator--operator to move backward one position at a time. The iterator returned by the list container is bidirectional.
5. Random-access iterators: Similar to a pointer
A random-access iterator has all the functions of a bidirectional iterator, plus a pointer-all function (a pointer is a random-access iterator), except that there is no "empty (null)" iterator and a null pointer corresponding to it. Basically, a random-access iterator can do anything like a pointer, including using the operator operator[] to index, add a value to a pointer to move forward or backward, or use comparison operators to compare between iterators.

The vectors and deque provided by Randomaccessiterator,list are provided by Bidirectionaliterator,set and map provide iterators is bidirectional Iterator, Hash_set and Hash_map iterators are Forward Iterator. The operations for iterator iterators in STL are as follows:

Iterator category	Description
Input iterator	Reads the element from the container. Input iterators can only read one element at a time and move forward, the input iterator supports only one pass, and the same input iterator cannot traverse a sequence two times
Output iterator
Forward iterator	Combines the functionality of the input iterator and output iterator and retains its position in the container
Bidirectional iterator	Functions of combining forward iterators and reverse iterators, supporting multiple passes
Random-access iterator	Combined bidirectional iterator functionality with direct access to any element in the container, You can skip forward and backward through any element

Operation of the iterator:

Each iterator can perform operations that include the previous iterator in the table. The operation of an iterator is essentially implemented by overloading the operator, and what the iterator supports and what it can do is determined by the operator overloaded by the iterator.

Iterator type	Type of operation	Description
All iterators	p++ ++p	Post-built self-increment iterators Predecessor self-increment iterator s ' s
Input iterators	*p P=p1 P==p1 P!=p1	Complex reference iterators, as Rvalue Assigning an iterator to another iterator Compare the equality of iterators Comparing the inequality of iterators
Output iterators	*p P=p1	Complex reference iterators, as Lvalue Assigning an iterator to another iterator
Forward iterators	Provides all the functions of an input-output iterator
Bidirectional iterators	--p p--	Pre-built-in self-reducing iterators Post-offset self-reducing iterators
Random-Access iterators	P+=i P-=i P+i P-i P[i] P<p1 P<=p1 P>p1 P>=p1	Increments the iterator I bit Decrements the iterator I bit Iterators after P-bit plus I-bit The iterator after the P-bit minus I bit Returns the element reference of the P-bit element deviating from the I bit Returns true if the position of the iterator P is before P1, otherwise false The position of P returns true at the front of the P1 or in the same position, otherwise it returns false Returns true if the position of the iterator P is P1, otherwise false The position of P returns true at the back of the P1 or in the same position, otherwise it returns false

Only sequential containers and associative containers support iterator traversal, and the categories of iterators supported by each container are as follows:
Iterator categories supported by container-supported iterator category containers for containers
Vector random Access deque random access list bidirectional
Set bidirectional multiset bidirectional map double To
Multimap bidirectional stack does not support queue not supported
Priority_queue does not support hash_set forward hash_map forward

Analysis of STL source code--classification of each container iterator