I have some simple code using std::string_view which works great in gcc10, but not in gcc8.
std::string_view was added to C++17 in GCC 7, so it should be possible to use this.
#include <string_view>
using sv = std::string_view;
sv ParseScheme(const sv& url)
{
sv pattern = "://";
if (auto found = url.find(pattern); found != sv::npos)
{
return sv(url.begin(), url.begin() + found);
}
return sv();
}
Compiling gives me:
$ g++ main.cpp --std=c++17 -Werror
main.cpp: In function 'sv ParseScheme(const sv&)':
main.cpp:9:44: error: invalid conversion from
'std::basic_string_view<char>::const_iterator' {aka 'const char*'} to
'std::basic_string_view<char>::size_type' {aka 'long unsigned int'} [-fpermissive]
return sv(url.begin(), url.begin() + found);
~~~~~~~~~~~~^~~~~~~
In file included from main.cpp:1:
/usr/include/c++/8/string_view:105:56: note: initializing argument 2 of
'constexpr std::basic_string_view<_CharT, _Traits>::basic_string_view(
const _CharT*, std::basic_string_view<_CharT, _Traits>::size_type
) [with
_CharT = char;
_Traits = std::char_traits<char>;
std::basic_string_view<_CharT, _Traits>::size_type = long unsigned int
]'
basic_string_view(const _CharT* __str, size_type __len) noexcept
~~~~~~~~~~^~~~~
Is there something I'm actually doing wrong, or are string_views in gcc8 just broken?
I could use -fpermissive to ignore the issue, but we compile with -Werror, so an -fpermissive warning will fail the build anyways.
The string_view(Iterator,Iterator) constructor used here was added in C++20. that's why it doesn't work in gcc8.
An alternative is to use the string_view(const char*, size_type) constructor availalbe in C++17:
#include <string_view>
using sv = std::string_view;
sv ParseScheme(const sv& url)
{
sv pattern = "://";
if (auto found = url.find(pattern); found != sv::npos)
{
return sv(url.data() + found, url.size() - found);
}
return sv();
}