Chapter2: Qt5 template library, tool classes and controls

2.1 String class The
 QString class stores 16-bit Unicode values ​​and provides a wealth of functions such as operations, queries and conversions.
 　　(1): QString provides a binary "+" operator for combining two strings
　　 (2): QString::append()
 　　(3): Another function for combining strings QString::sprintf( )
 　　(4): Qt also provides another convenient way to combine strings, using the QString::arg() function
 　　(5): QString also provides some other ways to combine strings, including
  　　　　insert()
  　　　　prepend()
 　　　　 replace()
 　　(6): Many times remove the blanks at both ends of a string ("\n" "\r" "\t" " ")
  　　　　QString::trimmed()
  　　　　QString::simplified()

 2.1.2 Query string data
  　　(1) The function QString::startsWith() judges whether a string starts with a certain string
   　　　　QString str="Welcome to you!";
   　　　　str.startsWith("Welcome",Qt::CaseSensitive ); //Return true
 　　 (2): function QString::endsWith()
 　　 (3): function QString::contains() to determine whether a specified string has appeared before
 　　 (4): It is also a common function to compare two strings
   　　　　operatr<(const QString&) operat
   　　　　<=(const QString&)
 　　　　  ......
 　　　　  ......
  　　　　 compare(const QString&,const QString&,Qt::CaseSensitivity);
 2.1.3 String conversion
 　　 (1): QString provides rich conversion functions. QString::toInt() QString::toDouble(),QString::toFloat(),QString::toLong(),toLongLong
  　　　　 QString str="125";
   　　　　bool ok;
  　　　　 int hex = str.toInt(&ok,16);
  　　　　 int dec = str.toInt(&ok,10); //ok = true,dec=125
 　　 (2): The conversion function of the character encoding provided by QString will return a const char* type version of QByteArray, that is, the constructor QByteArray (const char*) constructed QByteArray object; QByteArray supports the following conversion functions:
  　　　　 toAscii()
   　　　　toLatin1()
   　　　　toUtf8()
   　　　　toLocal8Bit()

 　　　　 The difference between a NULL string and an empty (empty) string:
  　　　　NULL: is to use the default constructor of QString or use "(const char*)0"
  　　　　Empty: is a string of size 0

2.2: Container class
 　　Note: Qt's QObject and other subclasses (such as QWidget and QDialog, etc.) cannot be stored in the container. Because QObject and other subclasses do not have copy constructors and assignment operators. A possible alternative is to store pointers to QObject and its subclasses.

 　　2.2.1 QList class, QLinkedList class and QVector class
  　　　　QList<T> maintains an array of pointers, the pointers stored in the array point to the contents of the list items stored in QList<T>
 　　　　 QLinkedList<T> is a linked list, which is not A contiguous block of memory holds data
  　　　　QVector<T>

 　　2.2.2 QMap class and QHash class
  　　　　QMap class and QHash class have very similar functions, their only difference is:
  　　　　(1): QHash has faster search speed than QMap
  　　　　(2): QHash stores data items in any order , and QMap always stores data in the order of keys;
  　　　　(3): QHash's key type Key must provide operator==() and a global qHash(Key) function, while QMap's key type Key must provide operator<() function

2.3 QVariant class
 　　QVariant class is similar to the union type of C++. It can not only store many Qt type values, including QColor QBrush, etc., but also store Qt container type values.

2.4 Calculation and regular expressions

•  2.4.1 Qt 5 Common Algorithms

  Qt's <QtAlgorithms> and <QtGlobal> templates provide some algorithms and functions.
  qAbs(a):
  qMax(b,c);
  qRound(b): Return an integer closest to a floating point number
  qSwap(bn,cn): Swap the values ​​of two numbers

•  2.4.2 Basic Regular Expressions
  • Qt's QRegExp is similar to the representation class of regular expressions. It is based on Perl's regular expression language and fully supports Unicode.
  •  The regular expression consists of:
    • expressions
    • quantifiers
    • assertions
•    (1): The simplest expression is a character

     [AEIOU]: Matches all uppercase vowels
     [^AEIOU]: Matches all non-vowel letters
     [az]: Matches all lowercase English letters

• (2): Quantifiers indicate the number of times an expression appears

    x[1,2]: Indicates that x can have at least one, at most two
    [A-Za-z_]+[A-Za-z_0-9]*: It is required to start with a letter or underscore, followed by letters, numbers and underscore
    which

• • "+": Indicates that [A-Za-z] appears at least once and can appear multiple times
  • "*": Indicates that [A-Za-z_0-9] can appear zero or more times
  • 　　
• (3) "^", "$", "\b" are all regular expression assertions
  • 　　
• 2.5 Controls
  • 2.5.1 Button Group
    • Push Button
    • Tool Button
    • Radio Button
    • Check Box
    • Command Link Button
    • Button Box
  • 2.5.2 Input space group
  • 2.5.3 Display Control Group
  • 2.5.4 Spatial interval groups
  • 2.5.5 Layout Management Group
  • 2.5.6 Container Group
  • 2.5.7 Project View Group
  • 2.5.8 Item Control Group

 

L2.1 String QString: Concept Analysis

　　L1: Implicit sharing