Attribute

Note

Section _Attribute (in _Utils) · Macros (no namespace) · Headers utils/attribute/

Short macros for the compiler attributes, defined from the C++ version used (c++20.hpp, c++17.hpp, c++14.hpp, fallback.hpp): an attribute not supported by the version becomes empty, so the code stays the same everywhere.

Table of Contents

• Function & variable
• Branch prediction
• Memory & pointers
• Deprecation
• Example

Function & variable

Macro	Attribute
_nodiscard	[[nodiscard]]
_noreturn	[[noreturn]] (on the first declaration)
_noinline	[[noinline]]
_unused	[[maybe_unused]]
_fallthrough	[[fallthrough]]
_hot / _cold	[[gnu::hot]] / [[gnu::cold]]
_hidden	[[gnu::visibility("hidden")]]
_ctor / _dtor	[[gnu::constructor]] / [[gnu::destructor]] (run before / after main)

Branch prediction

Macro	Usage
_likely / _unlikely	[[likely]] / [[unlikely]], after the condition: if (error) _unlikely {...}
_likely_c(c) / _unlikely_c(c)	__builtin_expect inside an expression
_expect(c, v)	__builtin_expect(c, v)
_assume(expr)	[[assume(expr)]]

Memory & pointers

Macro	Attribute
_alignas(n)	alignas(n) (ex: _alignas(std::hardware_destructive_interference_size), defined to 64 when the library doesn't provide it)
_packed	[[gnu::packed]]
_noaddress	[[no_unique_address]]
_nonnull(i)	[[gnu::nonnull(i)]]
_alloc_size(i) / _alloc_size_mul(i, j)	[[gnu::alloc_size(...)]]
_read_only(ptr, size) / _write_only(ptr, size)	[[gnu::access(...)]]

Deprecation

Macro	Description
_deprecated(info)	[[deprecated(info)]]
_migration(major, minor, fix)	Renamed API kept until the given version (~vX.Y.Z in the warning)
_legacy	Kept for backward compatibility, no removal planned

The deprecation warnings follow the warning defines (_Warning / _NoWarning).

Example

#define _Attribute
#include <utils/utils.hpp>

_hot _nodiscard int parse(const char* s)
{
    if (!s) _unlikely {return -1;}
    return 0;
}

_migration(4, 0, 0) inline int oldParse(const char* s) {return parse(s);}