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更新时间：2023-11-14 19:43:46
以下内容适用于Qt5.Qt4的行为是不同的，实际上是不正确的.
您需要选择:
是否要使用8位宽的 std :: string 或16位宽的 std :: wstring 或其他某种类型.
Whether you want the 8-bit wide std::string or 16-bit wide std::wstring, or some other type.
目标字符串中需要哪种编码?
What encoding is desired in your target string?
在内部， QString 存储UTF-16编码的数据，因此任何Unicode代码点都可以用一个或两个 QChar 表示.
Internally, QString stores UTF-16 encoded data, so any Unicode code point may be represented in one or two QChars.
常见案例:
本地编码的8位 std :: string (如:系统区域设置):
Locally encoded 8-bit std::string (as in: system locale):
std::string(str.toLocal8Bit().constData())
UTF-8编码的8位 std :: string :
str.toStdString()
这等效于:
std::string(str.toUtf8().constData())
UTF-16或UCS-4编码的 std :: wstring ，分别为16或32位宽.Qt选择16位和32位编码，以匹配平台的 wchar_t 宽度.
UTF-16 or UCS-4 encoded std::wstring, 16- or 32 bits wide, respectively. The selection of 16- vs. 32-bit encoding is done by Qt to match the platform's width of wchar_t.
str.toStdWString()
C ++ 11的U16或U32字符串-从Qt 5.5起:
U16 or U32 strings of C++11 - from Qt 5.5 onwards:
str.toStdU16String()
str.toStdU32String()
UTF-16编码的16位 std :: u16string -仅在Qt 5.4之前需要此hack:
UTF-16 encoded 16-bit std::u16string - this hack is only needed up to Qt 5.4:
std::u16string(reinterpret_cast<const char16_t*>(str.constData()))
此编码不包含字节顺序标记(BOM).
This encoding does not include byte order marks (BOMs).
在转换之前将BOM预先添加到 QString 本身很容易:
It's easy to prepend BOMs to the QString itself before converting it:
QString src = ...;
src.prepend(QChar::ByteOrderMark);
#if QT_VERSION < QT_VERSION_CHECK(5,5,0)
auto dst = std::u16string{reinterpret_cast<const char16_t*>(src.constData()),
src.size()};
#else
auto dst = src.toStdU16String();
如果您希望字符串很大，则可以跳过一个副本:
If you expect the strings to be large, you can skip one copy:
const QString src = ...;
std::u16string dst;
dst.reserve(src.size() + 2); // BOM + termination
dst.append(char16_t(QChar::ByteOrderMark));
dst.append(reinterpret_cast<const char16_t*>(src.constData()),
src.size()+1);
在两种情况下， dst 现在都可以移植到具有任意字节序的系统.
In both cases, dst is now portable to systems with either endianness.