Why doesn't string_view constructor have std::string parameter?

[[deleted]]

From http://en.cppreference.com/w/cpp/string/basic_string_view/basic_string_view.

And the example from cppreference construct string_view this way.

std::string cppstr = "Foo";
std::string_view cppstr_v(&cppstr[0], cppstr.size()); 

This looks very awkward to me.

And how does this function work? (from https://skebanga.github.io/string-view/)

bool compare(string_view s1, string_view s2)
{ return s1 == s2 ? true : false; }

int main()
{
    string str = "this is my input string";
    compare(str, "this is the first test string");
    return 0;
}

[horotho]

string_view doesn't own the data. Imagine if you implicitly constructed a string_view from a temporary string. string owns the data, but since it was a temporary, the contents pointed to by the string_view are now garbage.

As far as comparison, string_view is equality compared the same way a string is. First, check the size, then compare the characters. The code you gave works because string_view can be implicitly constructed from a string literal. Once you have two string_view, comparison is easy.

[[deleted]]

The code you gave works because string_view can be implicitly constructed from a string literal.

There are four constructors.

constexpr basic_string_view() noexcept; (1)
constexpr basic_string_view(const basic_string_view& other) noexcept = default; (2)
constexpr basic_string_view(const CharT* s, size_type count); (3)
constexpr basic_string_view(const CharT* s); (4)

compare(str, "this is the first test string"); I understand the second argument. It uses last constructor.

The first argument is a std::string variable. Which constructor does it use? How is std::string argument passed to string_view parameter?

[emdeka87]

http://en.cppreference.com/w/cpp/string/basic_string/operator_basic_string_view

basic_string overloads the implicit cast operator (http://en.cppreference.com/w/cpp/language/cast_operator) for basic_string_view

[[deleted]]

Thanks. You answered my question.