初始字串的 5 個方式
QString str1 = "The night train";// QT 常見初始方式

QString str2("A yellow rose"); // QT 常見初始方式

std::string s1 = "A blue sky"; // C++標準library
QString str3 = s1.c_str(); // 把string物件轉換成C語言形式的字串常數

std::string s2 = "A thick fog";
QString str4 = QString::fromLatin1(s2.data(), s2.size()); //將C++string轉換成Qstring

char s3[] = "A deep forest";
QString str5(s3); //將C 字符陣列轉換成QString


取得單一字符
QString a = "Eagle";

a[0]; //output "E"
a.at(0); // output "E"

字串長度
QString s1 = "Eagle";

s1.size(); // 5
s1.count(); // 5
s1.length(); // 5

字串取代
QString s1 = "There are %1 white roses";
s1.arg(12); // There are 12 white roses

QString s2 = "We have %1 lemons and %2 oranges";
s2.arg("one").arg("two");// We have one lemons and two oranges

擷取字串
QString str = "The night train";

str.right(5); //從右邊開始擷取5個字符
str.left(9); //從左邊開始擷取9個字符
str.mid(4, 5); //從第4個字符開始，取5個字符

QString str2("The big apple");
QStringRef sub(&str2, 0, 7); //從第0個字符開始，擷取7個字符
sub.toString(); //QStringRef class 只能讀不能修改，需轉成string

字串遍歷
QTextStream out(stdout);

QString str = "There are many stars.";

foreach (QChar qc, str) {
out << qc << " ";
}

for (QChar *it=str.begin(); it!=str.end(); ++it) {
out << *it << " " ;
}
//begin() 取得指向的開始位置

for (int i = 0; i < str.size(); ++i) {
out << str.at(i) << " ";
}

Output
T h e r e a r e m a n y s t a r s .
字串比較
QString a = "Rain";
QString b = "rain";
QString c = "rain\n";

QString::compare(a, b) == -32

QString::compare(a, b, Qt::CaseInsensitive) == 0

字串轉換
QString s1 = "12";
QString s2 = "15";
QString s3, s4;

s1.toInt() + s2.toInt() //27

int n1 = 30;
int n2 = 40;

s3.setNum(n1) + s4.setNum(n2) //3040

字串屬性
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++;
}
}

// 2 digits
// 13 letters
// 4 spaces
// 2 puncts 標點

字串編輯

QString str = "Lovely";

str.append(" season"); //在尾巴加入字串 Lovely season

str.remove(10, 3); //從第10字元開始，刪除3個字元 Lovely sea

str.replace(7, 3, "girl"); //從第7字元開始，取代字串 Lovely girl

str.clear(); // 清除字串

str.isEmpty(); //true

str.chop(1); //刪除最後第1個字元

字串對齊

leftJustified()/rightJustified()

QString field1 = "Name: ";
QString field2 = "Occupation: ";
QString field3 = "Residence: ";
QString field4 = "Marital status: ";

//取最長字串長度，填滿' '空白
int wSpace = field4.size();

out << field1.rightJustified(wSpace, ' ') << "Robert\n";
out << field2.rightJustified(wSpace, ' ') << "programmer\n";
out << field3.rightJustified(wSpace, ' ') << "New York\n";
out << field4.rightJustified(wSpace, ' ') << "single\n";

Output
Name: Robert
Occupation: programmer
Residence: New York
Marital status: single

HTML跳脫字元
QFile file("cprog.c");

if (!file.open(QIODevice::ReadOnly)) {

qWarning("Cannot open file for reading");
return 1;
}

QTextStream in(&file);

QString allText = in.readAll();
out << allText.toHtmlEscaped() << endl; //取代<, >, &

file.close();



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