这个 absl::StrCat 错误在哪里发生，在 Abseil 或 MSVC 中?

I 从字符数组创建string_view

// creat sv from vector;
std::vector<char> vec = { 'w', 'h', 'a', 't' };
char* char_ptr = vec.data();
size_t sz = vec.size();
std::string_view sview_obj = std::string_view(char_ptr, sz);

如果你写：

using namespace std::string_view_literals;
std::cout << absl::StrCat(sview_obj, "ever")    // Error
<< absl::StrCat(sview_obj, sview_obj) // Error
<< absl::StrCat("what", "ever"sv)     // Error
<< absl::StrCat("what"sv, "ever"sv)   // Error
<< absl::StrCat("what", "ever");      // Okey

MSVC 错误：

<source>(16): error C2039: 'string_view_literals': is not a member of 'std'
/opt/compiler-explorer/libs/abseilabsl/numeric/int128.h(231): note: see declaration of 'std'
<source>(16): error C2871: 'string_view_literals': a namespace with this name does not exist
<source>(18): error C2665: 'absl::StrCat': none of the 5 overloads could convert all the argument types
/opt/compiler-explorer/libs/abseilabsl/strings/str_cat.h(310): note: could be 'std::string absl::StrCat(const absl::AlphaNum &,const absl::AlphaNum &)'
<source>(18): note: while trying to match the argument list '(std::string_view, const char [5])'
<source>(19): error C2665: 'absl::StrCat': none of the 5 overloads could convert all the argument types
/opt/compiler-explorer/libs/abseilabsl/strings/str_cat.h(310): note: could be 'std::string absl::StrCat(const absl::AlphaNum &,const absl::AlphaNum &)'
<source>(19): note: while trying to match the argument list '(std::string_view, std::string_view)'
<source>(20): error C3688: invalid literal suffix 'sv'; literal operator or literal operator template 'operator ""sv' not found
<source>(21): error C3688: invalid literal suffix 'sv'; literal operator or literal operator template 'operator ""sv' not found

除了 MSVC 中似乎缺少operator""sv， 第 18 行和第 19 行有一个共同点：

std::cout << absl::StrCat(sview_obj, "ever")    // Error
<< absl::StrCat(sview_obj, sview_obj) // Error

错误：

<source>(18): error C2665: 'absl::StrCat': none of the 5 overloads could convert all the argument types
/opt/compiler-explorer/libs/abseilabsl/strings/str_cat.h(310): note: could be 'std::string absl::StrCat(const absl::AlphaNum &,const absl::AlphaNum &)'
<source>(18): note: while trying to match the argument list '(std::string_view, const char [5])'

当我在我的VC BuildTool(使用clang 8目标msvc(上编译时，它在这里提供了额外的线索。

In file included from C:/Program Files/C++ Source/abseil-cpp/absl/strings/ascii.cc:15:
C:Program FilesC++ Sourceabseil-cppabsl/strings/ascii.h(198,10):  error: no matching constructor for initialization of 'absl::string_view' (aka 'basic_string_view<char>')
return absl::string_view(it, str.end() - it);
^                 ~~~~~~~~~~~~~~~~~~
C:Program Files (x86)Microsoft Visual Studio2017BuildToolsVCToolsMSVC14.13.26128includexstring(809,12):  note: candidate constructor not viable: no known conversion from 'std::_String_view_iterator<std::char_traits<char> >' to 'const std::basic_string_view<char, std::char_traits<char> >::const_pointer' (aka 'const char *const') for 1st argument
constexpr basic_string_view(_In_reads_(_Count) const const_pointer _Cts, const size_type _Count)
^

在当前的 MSVCincludexstring中，似乎不可能从std::_String_view_iterator<std::char_traits<char> >转换为const std::basic_string_view<char, std::char_traits<char> >::const_pointer(又名const char *const

Clang和GCC对此很满意。

戈德博尔特

更新

根据Algirdas Preidžius和Hans Passant下面的评论，将godbolt编译器从MSVC 2017 RTM更改为MSVC Pre 2018后，sv文字现在都是OK键。

上面还提到了一个错误。

std::cout << absl::StrCat(sview_obj, "ever")    // Error

错误

<source>(18): error C2665: 'absl::StrCat': none of the 5 overloads could convert all the argument types
/opt/compiler-explorer/libs/abseilabsl/strings/str_cat.h(310): note: could be 'std::string absl::StrCat(const absl::AlphaNum &,const absl::AlphaNum &)'
<source>(18): note: while trying to match the argument list '(std::string_view, const char [5])'

金霹雳 2