string_view vs const string&

std::string_view and const std::string& are both used for read-only access to strings, but they have different use cases and benefits.

Use std::string_view when:

• You need to provide a unified interface for different string types (e.g., std::string, C-style strings, and string literals).
• Performance is critical, and you want to avoid unnecessary copying.
• You are working with substrings or portions of strings without copying.

Use const std::string& when:

• You are certain that your function will only accept std::string objects.
• The lifetime of the string is tightly controlled, and there is no risk of dangling references.

Here's an example comparing the two:

1#include <iostream>
2#include <string>
3#include <string_view>
4
5void printStringView(std::string_view sv) {
6  std::cout << sv << '\n';
7}
8
9void printConstStringRef(const std::string& str) {
10  std::cout << str << '\n';
11}
12
13int main() {
14  std::string str{"Hello, world"};
15
16  // Works with std::string
17  printStringView(str);
18
19    // Works with C-style string
20  printStringView("Hello, C-style string");
21
22  // Works with std::string
23  printConstStringRef(str);
24
25  // Error: incompatible types
26  // printConstStringRef("Hello, C-style string"); 
27}

1Hello, world
2Hello, C-style string
3Hello, world

In summary, std::string_view offers greater flexibility and efficiency when handling various string types and avoiding unnecessary copying.

However, const std::string& is straightforward and ideal for cases where you are sure only std::string objects will be used.