P1748R1
Fill in [delay.cpp] TODO in P1389

// compile-time constant
#define BUFFER_SIZE 256
// better as:
auto constexpr buffer_size = 256;

// named constants
#define RED   0xFF0000
#define GREEN 0x00FF00
#define BLUE  0x0000FF
// better as:
enum class Color { red = 0xFF0000, green = 0x00FF00, blue = 0x0000FF };

// inline function
#define SUCCEEDED(res) (res == 0)
// better as:
inline constexpr bool succeeded(int const res) { return res == 0; }

// generic function
#define IS_NEGATIVE(x) ((x) < 0)
// better as:
template <typename T>
bool is_negative(T x) {
   return x < T{};
}

All these macros have many possible pitfalls (see gcc docs), they hard to get right and they don’t obey scope and type rules. The C++ replacements are easier to get right and fit better into the general picture.

The only preprocessor usages that are necessary right at the beginning are:

• #include for textual inclusion of header files (at least until modules become the main tool for consuming external code)

• #ifndef for creating "include guards" to prevent multiple inclusion