Other Operations

string_view is modelled to be very similar to std::string. The view, however, is non-owning, so any operation that modifies the data cannot go into the API. Here’s a brief list of methods that you can use with this new type:

Iterators

Method	Description
cbegin(), begin()	Return an iterator to the first character
crbegin(), rbegin()	Return a reverse iterator to the first character of the reversed view. It corresponds to the last character of the sequence.
cend(), end()	Returns an iterator to a place after the last character of a sequence
crend(), rend()	Returns an iterator to the end of reversed sequence. It corresponds to a place before the first character

Note: all of the above methods are constexpr and const, so you always get a const iterator (even for begin() or end()).

Accessing Elements

Method	Description
operator[]	Returns a const reference to the character at the specified position. Bounds are not checked.
at()	Returns a const reference to the character at specified position with bound checking (might throw std::out_of_range)
front()	Returns a const reference to the first character of the sequence
back()	Returns a const reference to the last character of the sequence
data()	Returns a pointer to the underlying data

Note: If the view is empty then you’ll get undefined behaviour for operator[], front(), back() and data().

Size & Capacity

Method	Description
size()/length()	Returns the numbers of characters in a sequence
max_size()	The largest possible number of char-like objects that can be referred to by a basic_string_view.
empty()	Returns size == 0

Modifiers

Method	Description
remove_prefix(size_type n)	Equivalent to: data_ += n; size_ -= n;
remove_suffix(size_type n)	Equivalent to: size_ -= n;
swap(basic_string_view& s)	Exchanges the values of *this and s

Other

Method	Description
copy(charT* s, size_type n, size_type pos)	Copies n characters into s starting from pos. not constexpr
substr(size_type pos, size_type n)	Complexity O(1) and not O(n) as in std::string
compare(...) [^metelipsis]	Compares strings, similarly to std::basic_string::compare
find(...)	Returns position of the first occurence of the input string or basic_string_view::npos
rfind(...)	Returns position of the last occurence of the input string or basic_string_view::npos
find_first_of(...)	Returns position of the first character that is equal to any character from the input pattern or basic_string_view::npos
find_last_of(...)	Returns position of the last character that is equal to any character from the input pattern or basic_string_view::npos
find_first_not_of(...)	Returns position of the first character that is different to any character from the input pattern or basic_string_view::npos
find_last_not_of(...)	Returns position of the last character that is different to any character from the input pattern or basic_string_view::npos

[^metelipsis]: ellipsis (...) means that a method has several overloads.

Non-member functions:

Function	Description
comparison operators: ==, !=, <=, >=, <, >	Lexicographically compares two string views
operator <<	For ostream output

Key things about the above operations: Key things about the above methods, functions and types:

• All of the above methods (except for copy, operator << and std::hash specialisation) are also constexpr! With this capability, you might now work with contiguous character sequences in constant expressions.
• The above list is almost the same as all non-mutable string operations. However, there are two new methods: remove_prefix and remove_suffix - they are not const, and they modify the string_view object. Note that they still cannot modify the referenced data.
• operator[], at, front, back, data - are also const - thus you cannot change the underlying character sequence (it’s only “read access”). In std::string there are overloads for those methods that return a reference, so you get “write access”. That’s not possible with string_view.
• string_view also has specialisation for std::hash
• string_view has a string literal ""sv, and you can define a variable like auto sv = "hello"sv;

More in C++20! In C++20 we’ll get two new methods:

• starts_with()
• ends_with()

They are implemented both for std::basic_string_view and std::basic_string. As of August 2019 Clang 6.0, GCC 9.0 and VS 2019 16.2 support them.

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string_view offers a significant amount of functionality, but there are precautions which should be kept in mind while working with this type. The next lesson will help us understand this better.