Annex C (informative) Compatibility [diff]

Change: Character array extraction only takes array types.

Rationale: Increase safety via preventing buffer overflow at compile time.

Effect on original feature: Valid C++ 2017 code may fail to compile in this revision of C++.

For example: auto p = new char[100]; char q[100]; std::cin >> std::setw(20) >> p; // ill-formed; previously well-formed std::cin >> std::setw(20) >> q; // OK

Change: Overload resolution for ostream inserters used with UTF-8 literals.

Rationale: Required for new features.

Effect on original feature: Valid C++ 2017 code that passes UTF-8 literals to basic_ostream<char, ...>​::​operator<< or basic_ostream<wchar_t, ...>​::​operator<< is now ill-formed.

For example: std::cout << u8"text"; // previously called operator<<(const char*) and printed a string; // now ill-formed std::cout << u8'X'; // previously called operator<<(char) and printed a character; // now ill-formed

Change: Overload resolution for ostream inserters used with wchar_t, char16_t, or char32_t types.

Rationale: Removal of surprising behavior.

Effect on original feature: Valid C++ 2017 code that passes wchar_t, char16_t, or char32_t characters or strings to basic_ostream<char, ...>​::​operator<< or that passes char16_t or char32_t characters or strings to basic_ostream<wchar_t, ...>​::​operator<< is now ill-formed.

For example: std::cout << u"text"; // previously formatted the string as a pointer value; // now ill-formed std::cout << u'X'; // previously formatted the character as an integer value; // now ill-formed

Change: Return type of filesystem path format observer member functions.

Rationale: Required for new features.

Effect on original feature: Valid C++ 2017 code that depends on the u8string() and generic_u8string() member functions of std​::​filesystem​::​path returning std​::​string is not valid in this revision of C++.

For example: std::filesystem::path p; std::string s1 = p.u8string(); // ill-formed; previously well-formed std::string s2 = p.generic_u8string(); // ill-formed; previously well-formed