[[noreturn]] void unreachable();
(since C++23)Invokes undefined behavior at a given point.
An implementation may use this to optimize impossible code branches away (typically, in optimized builds) or to trap them to prevent further execution (typically, in debug builds).
[edit] Notes [edit] Possible implementation[[noreturn]] inline void unreachable()
{
// Uses compiler specific extensions if possible.
// Even if no extension is used, undefined behavior is still raised by
// an empty function body and the noreturn attribute.
#if defined(_MSC_VER) && !defined(__clang__) // MSVC
__assume(false);
#else // GCC, Clang
__builtin_unreachable();
#endif
}[edit] Example
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <utility>
#include <vector>
struct Color { std::uint8_t r, g, b, a; };
// Assume that only restricted set of texture caps is supported.
void generate_texture(std::vector<Color>& tex, std::size_t xy)
{
switch (xy)
{
case 128: [[fallthrough]];
case 256: [[fallthrough]];
case 512: /* ... */
tex.clear();
tex.resize(xy * xy, Color{0, 0, 0, 0});
break;
default:
std::unreachable();
}
}
int main()
{
std::vector<Color> tex;
generate_texture(tex, 128); // OK
assert(tex.size() == 128 * 128);
generate_texture(tex, 32); // Results in undefined behavior
}
Possible output:
[edit] See also specifies that the expression will always evaluate to true at a given pointRetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4