void Foo1(string_view view) {
...
}
string str = "one two three";
Foo1("one two three"); // Implicitly convert char* to string_view
Foo1(str);
I wonder which constructor converts char* to string_view implicitly and which one converts the string to string_view implicitly?
I know constructor (4) convert const char* to string_view but what I passed is char*.
std::string_view has a non-explicit converting constructor taking const char*, which supports implicit conversion from const char* to std::string_view.
constexpr basic_string_view(const CharT* s);
When you say:
but what I passed is
char*.
You're actually passing a string literal (i.e. "one two three"), whose type is const char[14] (including the null terminator '\0'), which could decay to const char*.
And std::string has a non-explicit conversion operator which supports implicit conversion from std::string to std::string_view.
constexpr operator std::basic_string_view<CharT, Traits>() const noexcept;
conversion operator special so that string to string_view is implicit? I notice basic_string also has c_str() function but that does not make string to char* implicit?
std::string defines a conversion operator to std::string_view, and it is implicit simply by virtue of the fact that it is not declared as explicit. std::string::c_str() is not a conversion operator, just a plain method. std::string does not define any conversion operator to char*, neither implicit nor explicit.It's https://en.cppreference.com/w/cpp/string/basic_string/operator_basic_string_view:
together with string_view's copy constructor (2)
Below is how it convert from std::basic_string to std::basic_string_view.
Copy from gcc-13.2.0/libstdc++-v3/include/bits/basic_string.h
/**
* @brief Convert to a string_view.
* @return A string_view.
*/
_GLIBCXX20_CONSTEXPR
operator __sv_type() const noexcept
{ return __sv_type(data(), size()); }
char*as you claim, any pointer-to-mutable is usable as a pointer-to-const (you can substitute reference for pointer there and that's also true). Theconstthere is a promise that the string view will not write to the pointed-to characters.