QString string related operations

1. Use a character to fill the string, which means that all characters in the string are replaced by ch of equal length.

   QString::fill(QChar ch, int size=-1)

	QString str = "Berlin";
    str.fill('z');	//str == "zzzzzz"
    str.fill('A', 2); 	//str == "AA"

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2. Find the same string str from the string

   int QString::indexOf ( const QString & str, int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const

 	QString x = "sticky question";
 	QString y = "sti";
 	x.indexOf(y);               // returns 0
 	x.indexOf(y, 1);            // returns 10
 	x.indexOf(y, 10);           // returns 10
 	x.indexOf(y, 11);           // returns -1

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3. Insert string at specified position

   QString & QString::insert ( int position, const QString & str )

 	QString str = "Meal";
 	str.insert(1, QString("ontr"));
 	// str == "Montreal"

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4. Determine whether the string is empty
   bool QString::isEmpty () const

 	QString().isEmpty();            // returns true
 	QString("").isEmpty();          // returns true
 	QString("x").isEmpty();         // returns false
 	QString("abc").isEmpty();       // returns false

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5. Determine whether the string exists

   bool QString::isNull () const

 	QString().isNull();             // returns true
 	QString("").isNull();           // returns false
 	QString("abc").isNull();        // returns false

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6. Intercept string from left to right
   QString QString::left (int n) const

 	QString x = "Pineapple";
 	QString y = x.left(4);      // y == "Pine"

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7. Intercept the string from the middle
   QString QString::mid (int position, int n = -1) const

 	QString x = "Nine pineapples";
 	QString y = x.mid(5, 4);            // y == "pine"
 	QString z = x.mid(5);               // z == "pineapples"

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8. Remove a character in the middle of the string
   QString & QString::remove (int position, int n)

 	QString s = "Montreal";
	s.remove(1, 4);
 	// s == "Meal"

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9. Replace some characters in the string
   QString & QString::replace (int position, int n, const QString & after)

 	QString x = "Say yes!";
 	QString y = "no";
 	x.replace(4, 3, y);
 	// x == "Say no!"

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10. Cut a string with a character
    QString QString::section (QChar sep, int start, int end = -1, SectionFlags flags = SectionDefault) const

	QString str;
	QString csv = "forename,middlename,surname,phone";
	QString path = "/usr/local/bin/myapp"; // First field is empty
	QString::SectionFlag flag = QString::SectionSkipEmpty;

	str = csv.section(',', 2, 2);   // str == "surname"
	str = path.section('/', 3, 4);  // str == "bin/myapp"
	str = path.section('/', 3, 3, flag); // str == "myapp"

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11. Convert integer, float or other types to QString
    QString & QString::setNum (uint n, int base = 10)

Similarly, there are many multi-loaded functions. If you want to learn more, you still have to read the Qt help documentation.