Table of contents
1. Basic usage of regular expressions
| character | describe |
|---|---|
| [ ] | Matches all characters in [ ]. Such as [123] is to match 1 or 2 or 3, match "2569431012" is to match all 1 or 2 or 3 numbers, that is, 2, 3, 1, 1, 2, not to match consecutive 123. |
| [^ ] | Matches all characters except [ ]. Such as [^ABC], means to match all characters except ABC. |
| [0-9] | represents an interval. |
| \d | Matches a numeric character. Equivalent to [0-9]. |
| \D | Matches a non-numeric character. Equivalent to [^0-9]. |
| . | Match any single character except newline (\n, \r). To match ".", such as IP address matching, you must use the escape character "\.". |
| \w | Match letters, numbers, underscores. Equivalent to [A-Za-z0-9]. |
| ^ | Matches the beginning of the input string. If used in a square bracket expression, such as [^ABC], it means to match all characters except ABC. To match the ^ character itself, use the escape character "\^". |
| $ | Matches the end of the input string. $ also matches '\n' or '\r' if the Multiline property of the QRegExp object is set. To match the $ character itself, use the escape character "\$". |
| + | Matches the preceding character or expression one or more times, equivalent to {1,}. |
| * | Matches the preceding character or expression zero or more times, equivalent to {0,}. Such as [0-9]* means any number of numbers |
| ? | Matches the preceding character or expression zero or one time, equivalent to {0, 1}. |
| {n} | n is a non-negative number, which means match the preceding character or expression n times. |
| {n,} | Indicates to match the previous character or expression at least n times |
| {n,m} | Both n and m are non-negative numbers, which means that the previous character or expression is matched at least n times and at most m times. |
| \b | Matches a word boundary, the position between a word and a space |
| \B | Non-word boundary matching |
Notice:C++中"\"在字符串中表示要用"\\"
2. Commonly used regular expressions
| describe | expression |
|---|---|
| number | ^[0-9]*$ |
| n-digit number | ^\d{n}$ |
| at least n digits | ^\d{n,}$ |
| mn digits | ^\d{m,n}$ |
| Numbers beginning with zero and non-zero | ^(0|[1-9][0-9]*)$ |
| Class D IP: 224.0.0.0~239.255.255.255 | ^(22[4-9]|23[0-9])(\.((\d)|([1-9]\d)|(1\d{2})|(2[0-4]\d)|(25[0-5]))){3}$ |
| IP | ((25[0-5]|2[0-4]\d|((1\d{2})|([1-9]?\d))).){3}(25[0-5]|2[0-4]\d|((1\d{2})|([1-9]?\d))) |
3. Regular expressions for IP addresses
IPv4 address format, the total length is 32 bits = 4 segments * 8 bits, each segment is separated by ., and each segment is a decimal value between 0-255.
Representing 0-255 with regular expressions can be divided into several pieces to consider separately:
| Value range | features | Regular writing |
|---|---|---|
| 0-9 | One digit, only one digit, the value is 0~9 | \d |
| 10-99 | Two digits, the tens digit is 1-9, and the ones digit is 0~9 | [1-9]\d |
| 100-199 | Three digits, the highest digit is 1, the tens digit is 0-9, and the ones digit is 0-9 | 1\d{2} |
| 200-249 | Three digits, the highest digit is 2, the tens digit is 0-4, and the ones digit is 0-9 | 2[0-4]\d |
| 250-255 | Three digits, the highest digit is 2, the tens digit is 5, and the ones digit is 0-5 | 25[0-5] |
So the regular notation for an IP address is as follows:
((25[0-5]|2[0-4]\d|((1\d{2})|([1-9]?\d))).){3}(25[0-5]|2[0-4]\d|((1\d{2})|([1-9]?\d)))
4. Basic usage of QRegExp
Example: Restrict input to numbers only for a LineEdit
QRegExp regExp("\\d*");
QValidator* pValidator = new QRegExpValidator(regExp, this);
ui->lineEdit->setValidator(pValidator);
For example: regular match D class IP: 224.0.0.0~239.255.255.255
QRegExp regExp("^(22[4-9]|23[0-9])(\\.((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))){3}$");
ui->lineEdit->setValidator(new QRegExpValidator(regExp, this));
Notice:C++中"\"在字符串中表示要用"\\"