【 QString接口大全】 Qt QString类使用示例

//Example 1 ___sprintf
 QString str;
 str.sprintf("%s","Welcome ");     //str = "Welcome "
 str.sprintf("%s"," to you! ");      //str = " to you! "
 str.sprintf("%s %s","Welcome "," to you! ");     //str = "Welcome  to you! "; 
 
 
//Example 1 ___arg
 
QString str;
str = "%1 %2";
 
str.arg("%1f", "Hello");        // returns "%1f Hello"
str.arg("%1f").arg("Hello");    // returns "Hellof %2"
 
//Example 2 ___arg
 
//在使用多个arg( )连接时，一定要注意，前面连接使用的arg( )里如果有“%+数字”的情况，后面的arg( )会同样替换！
str = QString("%1 %2").arg("%1World", "Hello");
qDebug()<<str;
//输出为："%1World Hello"
 
str = QString("%1 %2").arg("%1World").arg("Hello");
qDebug()<<str;
//输出为："HelloWorld %2"
//第一个arg执行完后变为：QString("%1World %2").arg("Hello")
//再次执行后"Hello"替换的为%1
 
 
//Example 3 ___arg
 
str = QString("十进制 63 的十进制为 %1")
            .arg(63, 0, 10);
//输出："十进制 63 的十进制为 63"
str = QString("十进制 63 的十六进制为 %1")
            .arg(63, 0, 16);
//输出："十进制 63 的十六进制为 3f"
str = QString("%1 %L2 %L3")
            .arg(12345)
            .arg(1987654321)  //根据结果，可知道这个L的作用
            .arg(12345, 0, 8); //但使用这种方式时，L失效
//输出为：12345 1,987,654,321 30071
//这里%L3的L没有任何作用

   QString str="hello";
   str+=" world";
   qDebug() <<str;     //str=hello world

   QString str="hello";
   str.append("world");
   qDebug() <<str;    //str=hello world

QString str1="ABC"，str2="EFG";
 
str1.prepend (str) ;
 
qDebug() <<str1;    //str1="EFGABC"

QString str1=" Are you OK? ", str2;
str2=str1.trimmed () ; //str1="Are you OK? "
str2=str1.simplified(); //str1="Are you OK?"

QString str = "white man";
str.insert(6,"strong ");

QString str = "white man";
str.remove(6,3);

QString & replace(int position, int n, const QString &after)
QString & replace(int position, int n, const QChar *unicode, int size)
QString & replace(int position, int n, QChar after)
QString & replace(QChar before, QChar after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(const QChar *before, int blen, const QChar *after, int alen, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(QLatin1String before, QLatin1String after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(QLatin1String before, const QString &after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(const QString &before, QLatin1String after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(const QString &before, const QString &after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(QChar ch, const QString &after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(QChar c, QLatin1String after, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString & replace(const QRegExp &rx, const QString &after)
QString & replace(const QRegularExpression &re, const QString &after)

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

QString toUpper() const
QString toLower() const

QString str1="Hello, World", str2;
str2=str1.toUpper(); //str1="HELLO,WORLD"
str2=str1.toLower(); //str1="hello, world"

    QByteArray array = tcpSocket->readAll();//从套接字读取数据
    QString strr = array;//将数据转换为QString格式
    QStringList strlist=strr.split(" ");//将数据以空格拆分，并放入数组中
    QStringList list=strlist.at(1).split("#");//将strlist中的第一号元素以“#”隔开并存入list中
    qDebug()<<list.at(0);//打印出list中的首个元素

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

QString str1="NI 好"
N=str1.count()  //N=3
N=str1.size() //N=3
N=str1.length() //N=3

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

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

QString str1="G:\Qt5Book\QT5.9Study\qw.cpp";
N=str1.contains (".cpp", Qt::CaseInsensitive) ; // N=true,不区分大小写
N=str1.contains (".CPP", Qt::CaseSensitive) ;  // N=false,区分大小写

QString str1=MG:\Qt5Book\QT5.9Study\qw.cpp";
N=str1.endsWith (".cpp", Qt::CaseInsensitive) ; // N=true，不区分大小写
N=str1.endsWith (".CPP", Qt::CaseSensitive) ; // N=false，区分大小写
N=str1.startsWith ("g: ") ; // N=true，缺省为不区分大小写

QString str2, str1="学生姓名,男,1984-3-4,汉族,山东";
str2=str1.section (",",0,0); // str2="学生姓名"， 第 1 段的编号为 0
str2=str1.section (",",1,1}; // str2="男"
str2=str1.section (",",0,1}; // str2="学生姓名，男"
str2=str1.section (",",4,4); // str2="山东"

QString str2, str1="学生姓名,男,1984-3-4,汉族,山东";
N=str1.indexOf (",") ; // N=4，第一个","出现的位置
str2=str1.left (N) ; //str2="学生姓名"
N=str1.lastIndexOf (",") ; // N=18，最后一个逗号的位置
str2=str1.right (str1.size()-N-1); //str2=”山东"，提取最后一个逗号之后的字符串

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

//QString转换String
 
string s = qstr.toStdString();
 
//String转换QString
 
QString qstr2 = QString::fromStdString(s);

QString str;  
QDateTime time;  
  
str = "2018-04-02 13:35:00";  
  
time = QDateTime::fromString(str, "yyyy-MM-dd hh:mm:ss"); 

/** 整数转换 **/
int a = 20;
uint b =255;
QString::number(a);
QString::number(a,10);
QString::number(b);
QString::number(b,16);
 
/** 浮点数转换 **/
float a;
QString::number(a,‘f’, 2); //保留2位小数
QString::number(a, ‘g’, 2); //保留2位有效数字，以简单方式表示，或者科学计数法表示
 
//保留指定位数（如001）,保留3位,不足在前面补0
QString str=QString::number(a).sprintf("%03d",a);//保留指定位数（如001）
 
QString str=QString("%1").arg(a, 3, 10, QChar('0'));

QString str;
str.setNum(1234);       // str == "1234"

QString str = "12";
int i = str.toInt();
 
//If ok is not nullptr, failure is reported by setting *ok to false, and success by setting *ok to true.
 
QString str = "1234.56";
double val = str.toDouble();   // val == 1234.56
//Warning: The QString content may only contain valid numerical characters which includes the plus/minus sign, the character e used in scientific notation, and the decimal point. Including the unit or additional characters leads to a conversion error.
 
bool ok;
double d;
 
d = QString( "1234.56e-02" ).toDouble(&ok); // ok == true, d == 12.3456
 
d = QString( "1234.56e-02 Volt" ).toDouble(&ok); // ok == false, d == 0
//The string conversion will always happen in the 'C' locale. For locale dependent conversion use QLocale::toDouble()
 
d = QString( "1234,56" ).toDouble(&ok); // ok == false
d = QString( "1234.56" ).toDouble(&ok); // ok == true, d == 1234.56
//For historical reasons, this function does not handle thousands group separators. If you need to convert such numbers, use QLocale::toDouble().
 
d = QString( "1,234,567.89" ).toDouble(&ok); // ok == false
d = QString( "1234567.89" ).toDouble(&ok); // ok == true
 
QString str1 = "1234.56";
str1.toFloat();             // returns 1234.56
 
bool ok;
QString str2 = "R2D2";
str2.toFloat(&ok);          // returns 0.0, sets ok to false
 
QString str3 = "1234.56 Volt";
str3.toFloat(&ok);          // returns 0.0, sets ok to false

QString = "(1178)"
str.toAscii().data();

QString str = R"(Hello\tWorld\n)";

QString str = "Hello\\tWorld\\n";