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Make the new QStringLiteral produce a non-temporary

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This is currently GCC-only code (the __extension ({ }) stuff), but it
was the only way I found to create a static variable and return it. I
had to add the QConstStringDataPtr container because I had to return a
pointer to the data -- it's impossible to return a reference through
this extension.

I could have returned a naked pointer directly too.

This isn't complete. GCC 4.6 is placing the string in the .data
section, not .rodata as we wanted. Investigating further.

Change-Id: I170030dca3eddbd69f6c879e952f652f7fe5d958
Reviewed-on: http://codereview.qt.nokia.com/1350
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
This commit is contained in:
Thiago Macieira 2011-07-07 19:51:09 +02:00 committed by Qt by Nokia
parent f3d6589068
commit 571785b31d
1 changed files with 33 additions and 10 deletions
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43
src/corelib/tools/qstring.h
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@ -90,32 +90,54 @@ struct QStringData {
inline const ushort *data() const { return d + sizeof(qptrdiff)/sizeof(ushort) + offset; }
};
template<int N> struct QConstStringData;
template<int N> struct QConstStringDataPtr
{
const QConstStringData<N> *ptr;
};
#if defined(Q_COMPILER_UNICODE_STRINGS)
#if defined(Q_CC_GNU)
// We need to create a QStringData in the .rodata section of memory
// and the only way to do that is to create a "static const" variable.
// To do that, we need the __extension__ {( )} trick which only GCC supports
# if defined(Q_COMPILER_UNICODE_STRINGS)
template<int n> struct QConstStringData
{
const QStringData str;
const char16_t data[n];
operator const QStringData &() const { return str; }
};
#define QStringLiteral(str) (const QConstStringData<sizeof(u"" str)/2>) \
{ { Q_REFCOUNT_INITIALIZER(-1), sizeof(u"" str)/2 -1, 0, 0, { 0 } }, u"" str }
# define QStringLiteral(str) \
__extension__ ({ \
enum { Size = sizeof(u"" str)/2 }; \
static const QConstStringData<Size> qstring_literal = \
{ { Q_REFCOUNT_INITIALIZER(-1), Size -1, 0, 0, { 0 } }, u"" str }; \
QConstStringDataPtr<Size> holder = { &qstring_literal }; \
holder; })
# elif defined(Q_OS_WIN) || (defined(__SIZEOF_WCHAR_T__) && __SIZEOF_WCHAR_T__ == 2) || defined(WCHAR_MAX) && (WCHAR_MAX - 0 < 65536)
// wchar_t is 2 bytes
#elif defined(Q_OS_WIN) || (defined(__SIZEOF_WCHAR_T__) && __SIZEOF_WCHAR_T__ == 2) || defined(WCHAR_MAX) && (WCHAR_MAX - 0 < 65536)
template<int n> struct QConstStringData
{
const QStringData str;
const wchar_t data[n];
operator const QStringData &() const { return str; }
};
#define QStringLiteral(str) (const QConstStringData<sizeof(L"" str)/2>) \
{ { Q_REFCOUNT_INITIALIZER(-1), sizeof(L"" str)/2 -1, 0, 0, { 0 } }, L"" str }
# define QStringLiteral(str) \
__extension__ ({ \
enum { Size = sizeof(L"" str)/2 }; \
static const QConstStringData<Size> qstring_literal = \
{ { Q_REFCOUNT_INITIALIZER(-1), Size -1, 0, 0, { 0 } }, L"" str }; \
QConstStringDataPtr<Size> holder = { &qstring_literal }; \
holder; })
# endif
#endif
#ifndef QStringLiteral
// not GCC, or GCC in C++98 mode with 4-byte wchar_t
// fallback, uses QLatin1String as next best options
#else
template<int n> struct QConstStringData
{
@ -123,8 +145,7 @@ template<int n> struct QConstStringData
const ushort data[n];
operator const QStringData &() const { return str; }
};
#define QStringLiteral(str) QLatin1String(str)
# define QStringLiteral(str) QLatin1String(str)
#endif
#ifndef QT_NO_KEYWORDS
@ -558,6 +579,8 @@ public:
QString(int size, Qt::Initialization);
template <int n>
inline QString(const QConstStringData<n> &dd) : d(const_cast<QStringData *>(&dd.str)) {}
template <int N>
inline QString(QConstStringDataPtr<N> dd) : d(const_cast<QStringData *>(&dd.ptr->str)) {}
private:
#if defined(QT_NO_CAST_FROM_ASCII) && !defined(Q_NO_DECLARED_NOT_DEFINED)