c++ - 如何将 std::string_view 转换为 QStringView

Question

我尝试了以下转换，但都给了我一个 no matching constructor for initialization of 'QStringView'错误(评论反射(reflect)了我试图调用的构造函数):

string someString = "hello world";
string_view strView( someString );

// QStringView(const Char (&)[N] string = N) or
// QStringView(const Char *str, qsizetype len)
QStringView qStrView1(strView.data(), strView.size());

// QStringView(const Char *first, const Char *last)
QStringView qStrView2(strView.data(), strView.data() + strView.size());

// QStringView(const Char *first, const Char *last)
QStringView qStrView3(strView.begin(), strView.end());
QStringView qStrView3a(strView.cbegin(), strView.cend());

// QStringView(const Char *str)
QStringView qStrView4(strView.data());

(我认为第 1 次或第 2 次转换可能会起作用，但出于失望而尝试了第 3 次和第 4 次转换。)

有人可以指点我正确的转换吗？我错过了什么吗？

或者我需要复制所有std::string s 为 QString s 并创建 QStringView从这些中，通过重用开始/结束位置？

(除此之外，我现在不知道如何将 QStringView 插入到 QTableWidgetItem 中。对于这个问题，我也将不胜感激。)

语境
我将文件内容读出为 std::string并根据分隔符将其拆分为字段行。为了有效地做到这一点，我生成了 std::vector的 std::string_view存储字段。现在我想在 Qt GUI 中可视化字符串(实际上是针对 QTableWidgetItem s)并认为 QStringView可能对 GUI 部分很有帮助。我想让 BusinessLogic 独立于 GUI，因此避免在那里包含任何 Qt 库。
环境

Qt 5.15.0

CONFIG += c++17

MSVC2019 amd64

window 10

错误
(我删除了 note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 2 were provided 、 note: candidate constructor template not viable: requires single argument 'str', but 2 arguments were provided 等)qStrView1 :

qstringview.h:173:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleCharType<char>::value' was not satisfied [with Char = char]
qstringview.h:178:22: note: candidate template ignored: could not match 'const Char *' against 'std::basic_string_view::size_type' (aka 'unsigned long long')
qstringview.h:191:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleArray<const char *>::value' was not satisfied [with Array = const char *]

qStrView2 :

qstringview.h:173:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleCharType<char>::value' was not satisfied [with Char = char]
qstringview.h:178:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleCharType<char>::value' was not satisfied [with Char = char]
qstringview.h:191:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleArray<const char *>::value' was not satisfied [with Array = const char *]

qStrView3 :

qstringview.h:173:22: note: candidate template ignored: could not match 'const Char *' against 'std::basic_string_view<char, std::char_traits<char> >::const_iterator' (aka '_String_view_iterator<std::char_traits<char> >')
qstringview.h:178:22: note: candidate template ignored: could not match 'const Char *' against 'std::basic_string_view<char, std::char_traits<char> >::const_iterator' (aka '_String_view_iterator<std::char_traits<char> >')
qstringview.h:191:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleArray<std::_String_view_iterator<std::char_traits<char> > >::value' was not satisfied [with Array = std::_String_view_iterator<std::char_traits<char> >]

qStrView3a :

qstringview.h:173:22: note: candidate template ignored: could not match 'const Char *' against 'std::basic_string_view<char, std::char_traits<char> >::const_iterator' (aka '_String_view_iterator<std::char_traits<char> >')
qstringview.h:178:22: note: candidate template ignored: could not match 'const Char *' against 'std::basic_string_view<char, std::char_traits<char> >::const_iterator' (aka '_String_view_iterator<std::char_traits<char> >')
qstringview.h:191:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleArray<std::_String_view_iterator<std::char_traits<char> > >::value' was not satisfied [with Array = std::_String_view_iterator<std::char_traits<char> >]

qStrView4 :

qstringview.h:103:7: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'std::basic_string_view<char, std::char_traits<char> >::const_pointer' (aka 'const char *') to 'const QStringView' for 1st argument
qstringview.h:103:7: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'std::basic_string_view<char, std::char_traits<char> >::const_pointer' (aka 'const char *') to 'QStringView' for 1st argument
qstringview.h:169:22: note: candidate constructor not viable: no known conversion from 'std::basic_string_view<char, std::char_traits<char> >::const_pointer' (aka 'const char *') to 'std::nullptr_t' (aka 'nullptr_t') for 1st argument
qstringview.h:196:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleArray<const char *>::value' was not satisfied [with Array = const char *]
qstringview.h:200:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatiblePointer<const char *>::value' was not satisfied [with Pointer = const char *]
qstringview.h:209:5: note: candidate template ignored: requirement 'std::is_same<const char *, QString>::value || std::is_same<const char *, QStringRef>::value' was not satisfied [with String = const char *]
qstringview.h:214:22: note: candidate template ignored: requirement 'QtPrivate::IsCompatibleStdBasicString<const char *>::value' was not satisfied [with StdBasicString = const char *]

Answer 1

感谢您将我指向 std::wstring .我花了一段时间才明白 wchar_t , wstring , wcout , wifstream , ... 的东西，但最后我有以下代码工作:
注意:仍然需要CONFIG += 17在 .pro 文件中，以下包括

#include <QStringView>
#include <string_view>
#include <string>

// create wstring and convert to QStringView
wstring somewstring = L"abc -ä-ö-ü-ß-";   //!< example string
wstring_view wview(somewstring);
// either work:
QStringView qstrv2a(wview.data(), wview.size());
QStringView qstrv2b(wview.data(), wview.data() + wview.size());

上述任何一个构造函数都可以正常工作。
在 QLabel 中使用 QStringView 的示例

// setup minimum GUI
QWidget* mainWidget = new QWidget(this);
setCentralWidget(mainWidget);
QVBoxLayout* mainLayout = new QVBoxLayout;
mainWidget->setLayout(mainLayout);

// create wstring and convert to QStringView
wstring somewstring = L"abc -ä-ö-ü-ß-";   //!< example string
wstring_view wview(somewstring);
// either work:
QStringView qstrv1(wview.data(), wview.size());

// convert to label
QLabel* otherLabel = new QLabel(qstrv1.toLocal8Bit());
mainLayout->addWidget(otherLabel);

从文件到 QLabel 的示例

// additinonal standard libararies:
#include <fstream>
#include <sstream>

// setup minimum GUI
QWidget* mainWidget = new QWidget(this);
setCentralWidget(mainWidget);
QVBoxLayout* mainLayout = new QVBoxLayout;
mainWidget->setLayout(mainLayout);

// read file with UTF-8 characters (to a std::string)
std::string tempFileContent;
ifstream file("./infile.txt", ios::binary);
file.seekg(0, file.end);
tempFileContent.resize(file.tellg());
file.seekg(0, file.beg);
file.read(&tempFileContent[0], tempFileContent.size());
file.close();

// convert std::string -> std::wstring
std::wstringstream wss;
wss << tempFileContent.c_str();
std::wstring fileContent = wss.str();

// convert std::wstring -> QStringView
// - either work:
QStringView qstrv2(fileContent.data(), fileContent.size());

// convert to label
QLabel* someLabel = new QLabel(qstrv2.toLatin1());    //!< WORKS                  
mainLayout->addWidget(someLabel);

/* these did not work:
// total garbage
QLabel(QString::fromUtf8(qstrv2.toString().toStdString().c_str()));

// misses just the 'ß'
QLabel* someLabel = new QLabel(qstrv2.toLocal8Bit());                                        
*/

文件内容在哪里

a-b-c-ä-ö-ü-ß-0-1-2

有趣的是读取带有 wifstream 的文本文件到 wstring比使用 wstringstream 将读取的字符串转换为 wstring 需要更长的时间。 (这仍然比读取 std::string 本身慢得多)