QString

QString的一些基本用法

#include <QTextStream>int main(void){   QTextStream out(stdout);      QString a = "love";      a.append(" chess");   a.prepend("I ");      out << a << endl;   out << "The a string has " << a.count()        << " characters" << endl;          out << a.toUpper() << endl;       out << a.toLower() << endl;      return 0;}

Output

$ ./basic I love chessThe a string has 12 charactersI LOVE CHESSi love chess

字符串初始化

字符串有几种初始化方法

#include <QTextStream>int main(void){   QTextStream out(stdout);      QString str1 = "The night train";   out << str1 << endl;      QString str2("A yellow rose");   out << str2 << endl;      std::string s1 = "A blue sky";   QString str3 = s1.c_str();    out << str3 << endl;      std::string s2 = "A thick fog";   QString str4 = QString::fromAscii(s2.data(), s2.size());   out << str4 << endl;      char s3[] = "A deep forest";   QString str5(s3);   out << str5 << endl;      return 0;}

Output

$ ./init The night trainA yellow roseA blue skyA thick fogA deep forest

字符串元素访问

access.cpp

#include <QTextStream>int main(void){   QTextStream out(stdout);      QString a = "Eagle";   out << a[0] << endl;   out << a[4] << endl;      out << a.at(0) << endl;      if (a.at(5).isNull()) {     out << "Outside the range of the string" << endl;     }            return 0;}

Output

$ ./access EeEOutside the range of the string

求字符串长度

length.cpp

#include <QTextStream>int main(){  QTextStream out(stdout);     QString s1 = "Eagle";  QString s2 = "Eagle\n";  QString s3 = "Eagle ";  QString s4 = "орел";  out << s1.length() << endl;  out << s2.length() << endl;  out << s3.length() << endl;  out << s4.length() << endl;    return 0;}

Output

$ ./length5668

字符串插值

#include <QTextStream>int main(){   QTextStream out(stdout);      QString s1 = "There are %1 white roses";   int n = 12;      out << s1.arg(n) << endl;      QString s2 = "The tree is %1m high";   double h = 5.65;      out << s2.arg(h) << endl;      QString s3 = "We have %1 lemons and %2 oranges";   int ln = 12;   int on = 4;      out << s3.arg(ln).arg(on) << endl;      return 0;}

Output

$ ./interpolation There are 12 white rosesThe tree is 5.65m highWe have 12 lemons and 4 oranges

求子串

substrings.cpp

#include <QTextStream>int main(void){   QTextStream out(stdout);      QString str = "The night train";      out << str.right(5) << endl;   out << str.left(9) << endl;   out << str.mid(4, 5) << endl;      QString str2("The big apple");   QStringRef sub(&str2, 0, 7);      out << sub.toString() << endl;      return 0;}

$ ./substrings trainThe nightnightThe big

Looping through strings

遍历字符串中的字符

#include <QTextStream>int main(void){  QTextStream out(stdout);     QString str = "There are many stars.";    foreach (QChar qc, str) {    out << qc << " ";    }    out << endl;    for (QChar *it=str.begin(); it!=str.end(); ++it) {    out << *it << " " ;  }    out << endl;    for (int i = 0; i < str.size(); ++i) {    out << str.at(i) << " ";      }    out << endl;    return 0;}

Output

$ ./loopingT h e r e   a r e   m a n y   s t a r s . T h e r e   a r e   m a n y   s t a r s . T h e r e   a r e   m a n y   s t a r s . 

字符串比较

comparing.cpp

#include <QTextStream>#define STR_EQUAL 0int main(void){   QTextStream out(stdout);      QString a = "Rain";   QString b = "rain";   QString c = "rain\n";      if (QString::compare(a, b) == STR_EQUAL) {     out << "a, b are equal" << endl;   } else {     out << "a, b are not equal" << endl;   }      out << "In case insensitive comparison:" << endl;      if (QString::compare(a, b, Qt::CaseInsensitive) == STR_EQUAL) {     out << "a, b are equal" << endl;   } else {     out << "a, b are not equal" << endl;   }           if (QString::compare(b, c) == STR_EQUAL) {     out << "b, c are equal" << endl;   } else {     out << "b, c are not equal" << endl;   }      c.chop(1);      out << "After removing the new line character" << endl;      if (QString::compare(b, c) == STR_EQUAL) {     out << "b, c are equal" << endl;   } else {     out << "b, c are not equal" << endl;   }                  return 0;}

$ ./comparing a, b are not equalIn case insensitive comparison:a, b are equalb, c are not equalAfter removing the new line characterb, c are equal

字符串和其他类型进行转换

Output

#include <QTextStream>int main(void){  QTextStream out(stdout);     QString s1 = "12";  QString s2 = "15";  QString s3, s4;    out << s1.toInt() + s2.toInt() << endl;     int n1 = 30;  int n2 = 40;    out << s3.setNum(n1) + s4.setNum(n2) << endl;     return 0;}

Output

$ ./converts 273040

字符类型

letters.cpp

#include <QTextStream>int main(void){  QTextStream out(stdout);     int digits  = 0;  int letters = 0;  int spaces  = 0;  int puncts  = 0;    QString str = "7 white, 3 red roses.";    foreach(QChar s, str)  {    if (s.isDigit()) {      digits++;    } else if (s.isLetter()) {      letters++;    } else if (s.isSpace()) {      spaces++;    } else if (s.isPunct()) {      puncts++;    }      }      out << QString("There are %1 characters").arg(str.count()) << endl;  out << QString("There are %1 letters").arg(letters) << endl;  out << QString("There are %1 digits").arg(digits) << endl;  out << QString("There are %1 spaces").arg(spaces) << endl;  out << QString("There are %1 punctuation characters").arg(puncts) << endl;      return 0;}


Output

$ ./letters There are 21 charactersThere are 13 lettersThere are 2 digitsThere are 4 spacesThere are 2 punctuation characters

字符串修改

#include <QTextStream>int main(void){   QTextStream out(stdout);      QString str = "Lovely";      str.append(" season");      out << str << endl;      str.remove(10, 3);   out << str << endl;   str.replace(7, 3, "girl");   out << str << endl;      str.clear();      if (str.isEmpty()) {     out << "The string is empty" << endl;   }      return 0;}

Output

$ ./modify Lovely seasonLovely seaLovely girlThe string is empty

Qt学习之路（2）------Qt中的字符串类