Qt学习之路（2）------Qt中的字符串类
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