Owned strings and borrowed string views

The idea

std::string owns its character storage, while std::string_view describes a sequence owned elsewhere. A view is cheap to copy, but copying it does not extend the owner’s lifetime. Use an owning string when the result must survive its source. These examples use C++17 or later and deliberately keep the owner unchanged while its views are used.

A view has an explicit length and need not end at a null terminator. Passing view.data() to an API that expects a terminated string can therefore expose characters beyond the view. Mutations that reallocate the owner can invalidate views just as they invalidate pointers. At an API boundary, document whether text is borrowed for the call or retained, and copy into owned storage before retaining it.

#include <iostream>
#include <string>
#include <string_view>
int main() {
  std::string owner = "bluebird";
  std::string_view view(owner.data(), 4);
  std::cout << view << ' ' << view.size() << '\n';
}

blue 4

The view selects four characters while owner retains their storage.