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<p class="MsoNormal"><span lang="EN-US">Hi, I’m using libc++ with gcc and have met a problem with code below:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">#include <string_view><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">constexpr bool test() {<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> const char s1[] = "mave";<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> std::string_view s2(s1);<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> return true;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">int main() {<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> static_assert(test());<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Error message was:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">$ g++ -nostdinc++ -I/home/yiyan/.local/include/c++/v1 -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc -std=c++17 --compile -o /dev/null 1.cc<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">1.cc: In function ‘int main()’:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">1.cc:8:23: error: non-constant condition for static assertion<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> 8 | static_assert(test());<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> | ~~~~^~<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">In file included from /home/yiyan/.local/include/c++/v1/string_view:175,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> from 1.cc:1:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">1.cc:8:23: in ‘constexpr’ expansion of ‘test()’<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">1.cc:4:27: in ‘constexpr’ expansion of ‘s2.std::__1::basic_string_view<char>::basic_string_view(((const char*)(& s1)))’<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">/home/yiyan/.local/include/c++/v1/string_view:238:46: in ‘constexpr’ expansion of ‘std::__1::char_traits<char>::length(__s)’<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas">/home/yiyan/.local/include/c++/v1/__string:217:69: error: ‘__builtin_strlen(((const char*)(& s1)))’ is not a constant expression<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> 217 | length(const char_type* __s) _NOEXCEPT {return __builtin_strlen(__s);}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:Consolas"> | ~~~~~~~~~~~~~~~~^~~~~<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Looks like the root cause is that </span>
<span lang="EN-US" style="font-family:Consolas">__builtin_strlen</span><span lang="EN-US"> is not constexpr in gcc.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Do you consider to fix this kind of issue?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Yichen<o:p></o:p></span></p>
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