How is a dangling pointer deduced in string_view?

Question

This reference states that the second example produces a dangling pointer. How is a dangling pointer created in the second expression but not in the first?

std::string_view good("a string literal");   // OK: "good" points to a static array
std::string_view bad("a temporary string"s); // "bad" holds a dangling pointer

Also, what is the character s after the string?

Answer 1

The s there is a user-defined literal operator that produces a std::string.

The difference between the two lines is that the good one is a string_view pointing to a string literal, and string literals have static lifetime (they last for the whole problem). The bad one is a string_view pointing to a temporary string, and that temporary owns its data - so when the temporary is destroyed (at the end of the line) it takes its data with it, and we end up with bad pointing to destroyed memory.

Answer 2

The s constructs a temporary std::string from the string literal. Once the execution reaches the semicolon, the temporary is destroyed and a dangling pointer is left in the std::string.

The L in front of the string literal creates a wide string. This is usually UTF-16 (Windows) or UTF-32 (Linux).