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diff --git a/devdocs/c/program%2Funreachable.html b/devdocs/c/program%2Funreachable.html deleted file mode 100644 index 09e33e03..00000000 --- a/devdocs/c/program%2Funreachable.html +++ /dev/null @@ -1,79 +0,0 @@ - <h1 id="firstHeading" class="firstHeading">unreachable</h1> <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code><stddef.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c23"> <td> <pre data-language="c">#define unreachable() /* see below */</pre> -</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c23">(since C23)</span> </td> </tr> </table> <p>The function-like macro <code>unreachable</code> expands to a <code>void</code> expression. Executing <code>unreachable()</code> results in <a href="../language/behavior" title="c/language/behavior">undefined behavior</a>.</p> -<p>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).</p> -<h3 id="Possible_implementation"> Possible implementation</h3> <table class="eq-fun-cpp-table"> <tr> <td> <div class="c source-c"><pre data-language="c">// Uses compiler specific extensions if possible. -#ifdef __GNUC__ // GCC, Clang, ICC - -#define unreachable() (__builtin_unreachable()) - -#elifdef _MSC_VER // MSVC - -#define unreachable() (__assume(false)) - -#else -// Even if no extension is used, undefined behavior is still raised by -// the empty function body and the noreturn attribute. - -// The external definition of unreachable_impl must be emitted in a separated TU -// due to the rule for inline functions in C. - -[[noreturn]] inline void unreachable_impl() {} -#define unreachable() (unreachable_impl()) - -#endif</pre></div> </td> -</tr> -</table> <h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <assert.h> -#include <stddef.h> -#include <stdint.h> -#include <stdlib.h> - -struct Color { uint8_t r, g, b, a; }; -struct ColorSpan { struct Color* data; size_t size; }; - -// Assume that only restricted set of texture caps is supported. -struct ColorSpan allocate_texture(size_t xy) -{ - switch (xy) - { - case 128: [[fallthrough]]; - case 256: [[fallthrough]]; - case 512: - { - /* ... */ - struct ColorSpan result = { - .data = malloc(xy * xy * sizeof(struct Color)), - .size = xy * xy - }; - if (!result.data) - result.size = 0; - return result; - } - default: - unreachable(); - } -} - -int main(void) -{ - struct ColorSpan tex = allocate_texture(128); // OK - assert(tex.size == 128 * 128); - - struct ColorSpan badtex = allocate_texture(32); // Undefined behavior - - free(badtex.data); - free(tex.data); -}</pre></div> <p>Possible output:</p> -<div class="text source-text"><pre data-language="c">Segmentation fault</pre></div> </div> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/utility/unreachable" title="cpp/utility/unreachable">C++ documentation</a></span> for <code>unreachable</code> </td> -</tr> </table> <h3 id="External_Links"> External Links</h3> <table> <tr style="vertical-align:top;"> <td>1. </td> <td> -<a rel="nofollow" class="external text" href="https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005funreachable">GCC docs: <code>__builtin_unreachable</code></a> </td> -</tr> <tr style="vertical-align:top;"> <td>2. </td> <td> -<a rel="nofollow" class="external text" href="https://clang.llvm.org/docs/LanguageExtensions.html#builtin-unreachable">Clang docs: <code>__builtin_unreachable</code></a> </td> -</tr> <tr style="vertical-align:top;"> <td>3. </td> <td> -<a rel="nofollow" class="external text" href="https://docs.microsoft.com/en-us/cpp/intrinsics/assume">MSVC docs: <code>__assume</code></a> </td> -</tr> -</table> <div class="_attribution"> - <p class="_attribution-p"> - © cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br> - <a href="https://en.cppreference.com/w/c/program/unreachable" class="_attribution-link">https://en.cppreference.com/w/c/program/unreachable</a> - </p> -</div> |