What is the C++ String view in C++ 17?

In C++, std::string is the standard way of working with strings as it gives users a lot of convenient functionalities to work with. std::string supports string operations such as searching for substrings, comparing strings, concatenating strings, and slicing strings (among many others).

However, std::string requires space to be dynamically allocated in the buffer and more memory to be dynamically allocated each time an operation is performed on the string.

What is `string_view`?

Conceptually, string_view is only a view of the string and cannot be used to modify the actual string. When a string_view is created, there’s no need to copy the data (unlike when you create a copy of a string). Furthermore, in terms of size on the heap,string_view is smaller than std::string.

Note: std::string_view cannot modify its underlying data and is only available in the C++ 17 version.

Why use `std::string_view`?

string_view is useful when you want to avoid unnecessary copies.
String_views are less memory-intensive to construct and copy. The creation of string_view from literals does not require a dynamic allocation.
Similarly, when creating a substring, std::string::substr returns a new string that potentially involves a dynamic allocation. However, we can construct a string_view from the address of a position in our string to make sure that no new memory will be dynamically allocated.

Code

The following code demonstrates how string_view helps save memory by preventing unnecessary dynamic allocations:

#include <iostream>
using namespace std;
int main() {
  std::string str = "The quick brown fox jumps over the lazy dog. And then runs away!!!";
  //'string::substr' returns a new string
  //this function is memory-intensive, specially if the string is realy long
  std::cout << str.substr(5, 15) << '\n';
  //The creation of string_view from the literals does not 
  //require a dynamic allocation.
  std::string_view sv = str;
  // string_view::substr returns a new string_view. No new memory allocated
  std::cout << sv.substr(5, 15) << '\n';
}

Free Resources

What is the C++ String view in C++ 17?

What is string_view?

Why use std::string_view?

Code

What is `string_view`?

Why use `std::string_view`?