Annex C (informative) Compatibility [diff]

Change: New kinds of string-literals.

Rationale: Required for new features.

Effect on original feature: Valid C++ 2003 code may fail to compile or produce different results in this revision of C++.

Specifically, macros named R, u8, u8R, u, uR, U, UR, or LR will not be expanded when adjacent to a string-literal but will be interpreted as part of the string-literal.

For example: #define u8 "abc" const char* s = u8"def"; // Previously "abcdef", now "def"

Change: User-defined literal string support.

Rationale: Required for new features.

Effect on original feature: Valid C++ 2003 code may fail to compile or produce different results in this revision of C++.

For example: #define _x "there" "hello"_x // #1

Previously, #1 would have consisted of two separate preprocessing tokens and the macro _x would have been expanded.

In this revision of C++, #1 consists of a single preprocessing token, so the macro is not expanded.

Change: New keywords.

Rationale: Required for new features.

Effect on original feature: Added to Table 5, the following identifiers are new keywords: alignas, alignof, char16_t, char32_t, constexpr, decltype, noexcept, nullptr, static_assert, and thread_local.

Valid C++ 2003 code using these identifiers is invalid in this revision of C++.

Change: Type of integer literals.

Rationale: C99 compatibility.

Effect on original feature: Certain integer literals larger than can be represented by long could change from an unsigned integer type to signed long long.