QString

QString的一些基本用法

basic.cpp

#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 chess
The a string has 12 characters
I LOVE CHESS
i love chess

字符串初始化

字符串有几种初始化方法

init.cpp

#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 train
A yellow rose
A blue sky
A thick fog
A 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
E
e
E
Outside 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

$ ./length
5
6
6
8

字符串插值

interpolation.cpp

#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 roses
The tree is 5.65m high
We 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;
}

Output

$ ./substrings
train
The night
night
The big

Looping through strings

遍历字符串中的字符

looping.cpp

#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

$ ./looping
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 .
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 0

int 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;
}

Output

$ ./comparing
a, b are not equal
In case insensitive comparison:
a, b are equal
b, c are not equal
After removing the new line character
b, 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
27
3040

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 characters
There are 13 letters
There are 2 digits
There are 4 spaces
There are 2 punctuation characters

字符串修改

modify.cpp

#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 season
Lovely sea
Lovely girl
The string is empty