Qt - 字符串（一）：相关的类
在Qt中与字符串操作相关的类有QLatin1Char，QLatin1String，QChar，QString，QByteArray，QStringRef， QStringList，QStringMatcher，QByteArrayMatcher
(1)QLatin1Char
QLatin1Char是个结构体，存储一个8位ASCII/Latin-1编码的字符，数据的存储类型为char
1 struct QLatin1Char 2 { 3 public: 4 inline explicit QLatin1Char(char c) : ch(c) {} 5 ...... 6 private: 7 char ch; 8 };
(2)QLatin1String
QLatin1String类提供了对US-ASCII/Latin-1编码字符串常量的封装
1 class Q_CORE_EXPORT QLatin1String 2 { 3 public: 4 inline explicit QLatin1String(const char *s) : chars(s) {} 5 ...... 6 inline const char *latin1() const { return chars; } 7 ...... 8 private: 9 const char *chars; 10 };
从类声明中可以看出，QLatin1String将数据存储为const char*的数据类型
(3)QChar
1 class Q_CORE_EXPORT QChar 2 { 3 ...... 4 private: 5 ...... 6 ushort ucs; 7 };
QChar存储一个16位（2个字节）的Unicode字符，数据的存储类型为ushort（unsigned short）
(4)QString
QString是Unicode编码的字符串，存储一系列16位的QChar，每一个QChar对应一个Unicode 4.0编码的字符
1 class Q_CORE_EXPORT QString 2 { 3 ...... 4 private: 5 ...... 6 struct Data { 7 QBasicAtomicInt ref; 8 int alloc, size; 9 ushort *data; // QT5: put that after the bit field to fill alignment gap; don't use sizeof any more then 10 ushort clean : 1; 11 ushort simpletext : 1; 12 ushort righttoleft : 1; 13 ushort asciiCache : 1; 14 ushort capacity : 1; 15 ushort reserved : 11; 16 // ### Qt5: try to ensure that "array" is aligned to 16 bytes on both 32- and 64-bit 17 ushort array[1]; 18 }; 19 static Data shared_null; 20 static Data shared_empty; 21 Data *d; 22 ...... 23 };
1 QString::QString(const QChar *unicode, int size) 2 { 3 if (!unicode) { 4 d = &shared_null; 5 d->ref.ref(); 6 } else if (size <= 0) { 7 d = &shared_empty; 8 d->ref.ref(); 9 } else { 10 d = (Data*) qMalloc(sizeof(Data)+size*sizeof(QChar)); 11 Q_CHECK_PTR(d); 12 d->ref = 1; 13 d->alloc = d->size = size; 14 d->clean = d->asciiCache = d->simpletext = d->righttoleft = d->capacity = 0; 15 d->data = d->array; 16 memcpy(d->array, unicode, size * sizeof(QChar)); 17 d->array[size] = '\0'; 18 } 19 }
（5）QByteArray
QByteArray是个字节数组，可以存储原始字节（包括一系列'\0')和传统的8位'\0'结尾的字符串，每一个字节存储为char类型的数据；
虽然QString用得更普遍和方便，但当需要存储原始的二进制数据或者内存保护要求严格时，用QByteArray比用QString更合适；
1 class Q_CORE_EXPORT QByteArray 2 { 3 private: 4 struct Data { 5 QBasicAtomicInt ref; 6 int alloc, size; 7 // ### Qt 5.0: We need to add the missing capacity bit 8 // (like other tool classes have), to maintain the 9 // reserved memory on resize. 10 char *data; 11 char array[1]; 12 }; 13 ...... 14 private: 15 ...... 16 static Data shared_null; 17 static Data shared_empty; 18 Data *d; 19 ...... 20 }
QByteArray始终会自动将数组最后一个字节存储为'\0'，但不包括在数组长度的计算中；
1 QByteArray::QByteArray(const char *str) 2 { 3 if (!str) { 4 d = &shared_null; 5 } else if (!*str) { 6 d = &shared_empty; 7 } else { 8 int len = qstrlen(str); 9 d = static_cast<Data *>(qMalloc(sizeof(Data)+len)); 10 Q_CHECK_PTR(d); 11 d->ref = 0;; 12 d->alloc = d->size = len; 13 d->data = d->array; 14 memcpy(d->array, str, len+1); // include null terminator 15 } 16 d->ref.ref(); 17 }
(6)QStringRef
QStringRef提供了对QString子字符串的封装，在一个QString字符串中指定起始位置和长度即可构造一个QStringRef
1 class Q_CORE_EXPORT QStringRef 2 { 3 const QString *m_string; 4 int m_position; 5 int m_size; 6 public: 7 inline QStringRef():m_string(0), m_position(0), m_size(0){} 8 ...... 9 };
(7)QStringList
1 class QStringList : public QList<QString> 2 { 3 ...... 4 };
(8)QStringMatcher
字符串匹配类，当需要循环反复匹配一个字符串或者一串字符，则可以用到这个类
1 class Q_CORE_EXPORT QStringMatcher 2 { 3 ...... 4 private: 5 QStringMatcherPrivate *d_ptr; 6 QString q_pattern; 7 Qt::CaseSensitivity q_cs; 8 #ifdef Q_CC_RVCT 9 // explicitly allow anonymous unions for RVCT to prevent compiler warnings 10 # pragma push 11 # pragma anon_unions 12 #endif 13 struct Data { 14 uchar q_skiptable[256]; 15 const QChar *uc; 16 int len; 17 }; 18 union { 19 uint q_data[256]; 20 Data p; 21 }; 22 #ifdef Q_CC_RVCT 23 # pragma pop 24 #endif 25 }
(9)QByteArrayMatcher
QByteArrayMatcher与QStringMatcher类似，不同之处在于它匹配的对象不是字符，是字节
1 class Q_CORE_EXPORT QByteArrayMatcher 2 { 3 ...... 4 private: 5 QByteArrayMatcherPrivate *d; 6 QByteArray q_pattern; 7 #ifdef Q_CC_RVCT 8 // explicitly allow anonymous unions for RVCT to prevent compiler warnings 9 # pragma push 10 # pragma anon_unions 11 #endif 12 struct Data { 13 uchar q_skiptable[256]; 14 const uchar *p; 15 int l; 16 }; 17 union { 18 uint dummy[256]; 19 Data p; 20 }; 21 #ifdef Q_CC_RVCT 22 # pragma pop 23 #endif 24 };
