Use of regular expressions in QT

QRegExp class

# The header file #include
#.pro Add... To the file QT += core
There are several common function interfaces

How to use function interfaces

Rules in regular expressions

regexp By expression 、 Quantifiers and assertions Built .
Anchor assertion ：^( The starting point ) and $( The end point ), These two symbols are not used to match the characters of the string , Instead, it is used to match the position in the string .

int indexIn(const QString &str, int offset = 0, QRegExp::CaretMode caretMode = CaretAtZero) const
effect : distinguish str Whether it matches the expression
offset: from str Subscripts in strings offset Start identifying ,offset The default is 0
Return value : The starting position of the recognition , If not identified as -1

bool exactMatch(const QString &str) const
effect : Equate to indexln()

QString cap(int nth = 0) const
effect : Returns the captured text string

QStringList QRegExp::capturedTexts() const
effect : Returns a list of captured text strings . The first string in the list is the entire matching string . Each subsequent list element contains a string , The string matches regexp One of the ( The captured ) subexpression .

int captureCount() const
effect : Number of recognition characters

bool isValid() const
effect : Judge whether the regular expression is reasonable

int matchedLength() const
effect : The length and size of the recognized character

Substitution of common symbols

Symbol	effect	Example
{x,y}	Represents the number of occurrences ,x Minimum number of times ,y Is the maximum number of times	[0-9]{1,2}
？	Represents matching the previous subexpression 0 Time or 1 Time , Equivalent to {0,1}	[0-9][0-9]?
*	Represents zero or more times that the preceding subexpression is matched , Equivalent to {0,}	hello(world)*
+	Represents matching the previous subexpression one or more times , Equivalent to {1,}	hello(world)+
-	Represents the range of characters	[a-z]
^	If ^ stay [] Inside , Then the subexpression performs inverse operation	[^abc]
|	perhaps	(hello|bye)
\b	Assertions are used only for judgment and do not match any characters

character	Abbreviation
[0-9]	\d
[^0-9]	\D
All blank symbols	\s
All non whitespace characters are good	\S
Match a line break	\n
Match a tab	\t
character 、 Numbers 、 Underline	\w
The character 、 Numbers 、 Underline	\W

Project practice

Learn regular expressions this time , In order to create multiple text boxes for the project, you need to enter text in a certain format , So it's better to use regular expressions to judge .

1、 For example, judge whether the color format entered in the text box is correct (0xFFFFFF)
The regular expression is written as :^(0x|0X)[0-9A-Fa-f]{6,6}$

QString content = ui->lineEdit->text();
QRegExp rx("^(0x|0X)[0-9A-Fa-f]{6,6}$");
if (rx.indexIn(content) == -1) {
    
   QMessageBox::warning(this,"",tr(" The color format is :0xFFFFFF"));
   return;
}

2、 For example, judge the code number entered in the text box （yue12345678）. Conditions : No less than two digits and no spaces 、 comma 、 Underline and other symbols , And the end can only be at least two digits
Xiaobai really can't think of a regular expression to meet the above conditions , Only two expressions can be used to judge whether the end is two numbers .

 QRegExp rxLen("\\d{2,15}$");
 QRegExp rxchinese("^[1-9A-Za-z][A-Za-z0-9]*[0-9]{1,15}$");
 if (rxLen.indexIn(str) != -1 && rxchinese.indexIn(str) != -1) {
    
        QString numStr = rxLen.cap();
        if (QString("%1").arg(numStr.toInt() + ui->sampleCountEdit->text().toInt()).size() != numStr.size()) {
    
              QMessageBox::warning(this,"",tr(" Wrong number format , The number cannot have spaces , Underline , Chinese and other characters , Such as yue123456"));
              return;
        }
 }

3、 Next, write some common requirements expressions , such as

demand	expression
Only numbers can be entered in the input box	^\d$
The input box can only enter characters	^[A-Za-z]+$
The input box can only be numeric and 26 A string of English letters	^[0-9A-Za-z]+$
The input box can only input Chinese	^[\u4e00-\u9fa5]{0,}$
Enter an integer or a value with at most two decimal places in the input box	^[0-9]+(.[0-9]{0,2})?$
Enter a negative number or an integer in the input box 、 Values with up to two decimal places	^(-)?[0-9]+(.[0-9]{0,2})?$
Enter the date format in the input box	^[1-9]{1}[0-9]{3}-(0?[1-9]|1[0-2])-(0?[1-9]|[1-2][1-9]|3[0-1])$