diff options
Diffstat (limited to 'src/corelib/tools/qstring.cpp')
| -rw-r--r-- | src/corelib/tools/qstring.cpp | 103 |
1 files changed, 82 insertions, 21 deletions
diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp index 6ae3c38..38b6f58 100644 --- a/src/corelib/tools/qstring.cpp +++ b/src/corelib/tools/qstring.cpp @@ -1,7 +1,7 @@ /**************************************************************************** ** ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). -** Contact: Qt Software Information (qt-info@nokia.com) +** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the QtCore module of the Qt Toolkit. ** @@ -34,7 +34,7 @@ ** met: http://www.gnu.org/copyleft/gpl.html. ** ** If you are unsure which license is appropriate for your use, please -** contact the sales department at qt-sales@nokia.com. +** contact the sales department at http://www.qtsoftware.com/contact. ** $QT_END_LICENSE$ ** ****************************************************************************/ @@ -169,7 +169,7 @@ static int ucstricmp(const ushort *a, const ushort *ae, const uchar *b) // Unicode case-insensitive comparison static int ucstrcmp(const QChar *a, int alen, const QChar *b, int blen) { - if (a == b) + if (a == b && alen == blen) return 0; int l = qMin(alen, blen); while (l-- && *a == *b) @@ -663,6 +663,74 @@ const QString::Null QString::null = { }; formats, the \e precision represents the maximum number of significant digits (trailing zeroes are omitted). + \section1 More Efficient String Construction + + Using the QString \c{'+'} operator, it is easy to construct a + complex string from multiple substrings. You will often write code + like this: + + \snippet doc/src/snippets/qstring/stringbuilder.cpp 0 + + There is nothing wrong with either of these string constructions, + but there are a few hidden inefficiencies. Beginning with Qt 4.6, + you can eliminate them. + + First, multiple uses of the \c{'+'} operator usually means + multiple memory allocations. When concatenating \e{n} substrings, + where \e{n > 2}, there can be as many as \e{n - 1} calls to the + memory allocator. + + Second, QLatin1String does not store its length internally but + calls qstrlen() when it needs to know its length. + + In 4.6, an internal template class \c{QStringBuilder} has been + added along with a few helper functions. This class is marked + internal and does not appear in the documentation, because you + aren't meant to instantiate it in your code. Its use will be + automatic, as described below. The class is found in + \c {src/corelib/tools/qstringbuilder.cpp} if you want to have a + look at it. + + \c{QStringBuilder} uses expression templates and reimplements the + \c{'%'} operator so that when you use \c{'%'} for string + concatenation instead of \c{'+'}, multiple substring + concatenations will be postponed until the final result is about + to be assigned to a QString. At this point, the amount of memory + required for the final result is known. The memory allocator is + then called \e{once} to get the required space, and the substrings + are copied into it one by one. + + \c{QLatin1Literal} is a second internal class that can replace + QLatin1String, which can't be changed for compatibility reasons. + \c{QLatin1Literal} stores its length, thereby saving time when + \c{QStringBuilder} computes the amount of memory required for the + final string. + + Additional efficiency is gained by inlining and reduced reference + counting (the QString created from a \c{QStringBuilder} typically + has a ref count of 1, whereas QString::append() needs an extra + test). + + There are three ways you can access this improved method of string + construction. The straightforward way is to include + \c{QStringBuilder} wherever you want to use it, and use the + \c{'%'} operator instead of \c{'+'} when concatenating strings: + + \snippet doc/src/snippets/qstring/stringbuilder.cpp 5 + + A more global approach is to include this define: + + \snippet doc/src/snippets/qstring/stringbuilder.cpp 3 + + and use \c{'%'} instead of \c{'+'} for string concatenation + everywhere. The third approach, which is the most convenient but + not entirely source compatible, is to include two defines: + + \snippet doc/src/snippets/qstring/stringbuilder.cpp 4 + + and the \c{'+'} will automatically be performed as the + \c{QStringBuilder} \c{'%'} everywhere. + \sa fromRawData(), QChar, QLatin1String, QByteArray, QStringRef */ @@ -946,14 +1014,13 @@ QString::QString(int size, QChar ch) } } -/*! - Constructs a string of the given \a size without initializing the - characters. This is only used in \c QStringBuilder::toString(). +/*! \fn QString::QString(int size, Qt::Initialization) + \internal - \internal + Constructs a string of the given \a size without initializing the + characters. This is only used in \c QStringBuilder::toString(). */ - -QString::QString(int size, Uninitialized) +QString::QString(int size, Qt::Initialization) { d = (Data*) qMalloc(sizeof(Data)+size*sizeof(QChar)); d->ref = 1; @@ -3784,8 +3851,7 @@ QString QString::fromUtf8(const char *str, int size) if (size < 0) size = qstrlen(str); - QString result; - result.resize(size); // worst case + QString result(size, Qt::Uninitialized); // worst case ushort *qch = result.d->data; uint uc = 0; uint min_uc = 0; @@ -3900,8 +3966,7 @@ QString QString::fromUcs4(const uint *unicode, int size) ++size; } - QString s; - s.resize(size*2); // worst case + QString s(size * 2, Qt::Uninitialized); // worst case ushort *uc = s.d->data; for (int i = 0; i < size; ++i) { uint u = unicode[i]; @@ -3964,8 +4029,7 @@ QString QString::simplified() const { if (d->size == 0) return *this; - QString result; - result.resize(d->size); + QString result(d->size, Qt::Uninitialized); const QChar *from = (const QChar*) d->data; const QChar *fromend = (const QChar*) from+d->size; int outc=0; @@ -4817,8 +4881,7 @@ QString QString::toLower() const c = QChar::surrogateToUcs4(*(p - 1), c); const QUnicodeTables::Properties *prop = qGetProp(c); if (prop->lowerCaseDiff || prop->lowerCaseSpecial) { - QString s; - s.resize(d->size); + QString s(d->size, Qt::Uninitialized); memcpy(s.d->data, d->data, (p - d->data)*sizeof(ushort)); ushort *pp = s.d->data + (p - d->data); while (p < e) { @@ -4909,8 +4972,7 @@ QString QString::toUpper() const c = QChar::surrogateToUcs4(*(p - 1), c); const QUnicodeTables::Properties *prop = qGetProp(c); if (prop->upperCaseDiff || prop->upperCaseSpecial) { - QString s; - s.resize(d->size); + QString s(d->size, Qt::Uninitialized); memcpy(s.d->data, d->data, (p - d->data)*sizeof(ushort)); ushort *pp = s.d->data + (p - d->data); while (p < e) { @@ -6207,8 +6269,7 @@ static QString replaceArgEscapes(const QString &s, const ArgEscapeData &d, int f + d.locale_occurrences *qMax(abs_field_width, larg.length()); - QString result; - result.resize(result_len); + QString result(result_len, Qt::Uninitialized); QChar *result_buff = (QChar*) result.unicode(); QChar *rc = result_buff; |