Qt 5.6 | Qt Core | C++ Classes | QRegularExpression

Qt 5.6.2 Reference Documentation

# QRegularExpression Class

The QRegularExpression class provides pattern matching using regular expressions. More...

Header: | #include <QRegularExpression>
qmake: | QT += core
Since: | Qt 5.0

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Types

enum | MatchOption { NoMatchOption, AnchoredMatchOption, DontCheckSubjectStringMatchOption }
flags | MatchOptions
enum | MatchType { NormalMatch, PartialPreferCompleteMatch, PartialPreferFirstMatch, NoMatch }
enum | PatternOption { NoPatternOption, CaseInsensitiveOption, DotMatchesEverythingOption, MultilineOption, ..., DontAutomaticallyOptimizeOption }
flags | PatternOptions

## Public Functions

| QRegularExpression()
| QRegularExpression(const QString &pattern, PatternOptions options = NoPatternOption)
| QRegularExpression(const QRegularExpression &re)
| ~QRegularExpression()
int | captureCount() const
QString | errorString() const
QRegularExpressionMatchIterator | globalMatch(const QString &subject, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const
QRegularExpressionMatchIterator | globalMatch(const QStringRef &subjectRef, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const
bool | isValid() const
QRegularExpressionMatch | match(const QString &subject, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const
QRegularExpressionMatch | match(const QStringRef &subjectRef, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const
QStringList | namedCaptureGroups() const
void | optimize() const
QString | pattern() const
int | patternErrorOffset() const
PatternOptions | patternOptions() const
void | setPattern(const QString &pattern)
void | setPatternOptions(PatternOptions options)
void | swap(QRegularExpression &other)
bool | operator!=(const QRegularExpression &re) const
QRegularExpression & | operator=(const QRegularExpression &re)
QRegularExpression & | operator=(QRegularExpression &&re)
bool | operator==(const QRegularExpression &re) const

## Static Public Members

QString | escape(const QString &str)

## Related Non-Members

uint | qHash(const QRegularExpression &key, uint seed = 0)
QDataStream & | operator<<(QDataStream &out, const QRegularExpression &re)
QDebug | operator<<(QDebug debug, const QRegularExpression &re)
QDebug | operator<<(QDebug debug, QRegularExpression::PatternOptions patternOptions)
QDataStream & | operator>>(QDataStream &in, QRegularExpression &re)

## Detailed Description

The QRegularExpression class provides pattern matching using regular expressions.

Regular expressions, or regexps, are a very powerful tool to handle strings and texts. This is useful in many contexts, e.g.,

Validation | A regexp can test whether a substring meets some criteria, e.g. is an integer or contains no whitespace.
Searching | A regexp provides more powerful pattern matching than simple substring matching, e.g., match one of the words mail, letter or correspondence, but none of the words email, mailman, mailer, letterbox, etc.
Search and Replace | A regexp can replace all occurrences of a substring with a different substring, e.g., replace all occurrences of & with &amp; except where the & is already followed by an amp;.
String Splitting | A regexp can be used to identify where a string should be split apart, e.g. splitting tab-delimited strings.

This document is by no means a complete reference to pattern matching using regular expressions, and the following parts will require the reader to have some basic knowledge about Perl-like regular expressions and their pattern syntax.

Good references about regular expressions include:

- Mastering Regular Expressions (Third Edition) by Jeffrey E. F. Friedl, ISBN 0-596-52812-4;
- the pcrepattern(3) man page, describing the pattern syntax supported by PCRE (the reference implementation of Perl-compatible regular expressions);
- the Perl's regular expression documentation and the Perl's regular expression tutorial.

### Introduction

QRegularExpression implements Perl-compatible regular expressions. It fully supports Unicode. For an overview of the regular expression syntax supported by QRegularExpression, please refer to the aforementioned pcrepattern(3) man page. A regular expression is made up of two things: a pattern string and a set of pattern options that change the meaning of the pattern string.

You can set the pattern string by passing a string to the QRegularExpression constructor:

      QRegularExpression re("a pattern");

This sets the pattern string to `a pattern`. You can also use the setPattern() function to set a pattern on an existing QRegularExpression object:

      QRegularExpression re;
      re.setPattern("another pattern");

Note that due to C++ literal strings rules, you must escape all backslashes inside the pattern string with another backslash:

      // matches two digits followed by a space and a word
      QRegularExpression re("\\d\\d \\w+");

      // matches a backslash
      QRegularExpression re2("\\\\");

The pattern() function returns the pattern that is currently set for a QRegularExpression object:

      QRegularExpression re("a third pattern");
      QString pattern = re.pattern(); // pattern == "a third pattern"

### Pattern Options

The meaning of the pattern string can be modified by setting one or more pattern options. For instance, it is possible to set a pattern to match case insensitively by setting the QRegularExpression::CaseInsensitiveOption.

You can set the options by passing them to the QRegularExpression constructor, as in:

      // matches "Qt rocks", but also "QT rocks", "QT ROCKS", "qT rOcKs", etc.
      QRegularExpression re("Qt rocks", QRegularExpression::CaseInsensitiveOption);

Alternatively, you can use the setPatternOptions() function on an existing QRegularExpressionObject:

      QRegularExpression re("^\\d+$");
      re.setPatternOptions(QRegularExpression::MultilineOption);
      // re matches any line in the subject string that contains only digits (but at least one)

It is possible to get the pattern options currently set on a QRegularExpression object by using the patternOptions() function:

      QRegularExpression re = QRegularExpression("^two.*words$", QRegularExpression::MultilineOption
                                                                 | QRegularExpression::DotMatchesEverythingOption);

      QRegularExpression::PatternOptions options = re.patternOptions();
      // options == QRegularExpression::MultilineOption | QRegularExpression::DotMatchesEverythingOption

Please refer to the QRegularExpression::PatternOption enum documentation for more information about each pattern option.

### Match Type and Match Options

The last two arguments of the match() and the globalMatch() functions set the match type and the match options. The match type is a value of the QRegularExpression::MatchType enum; the "traditional" matching algorithm is chosen by using the NormalMatch match type (the default). It is also possible to enable partial matching of the regular expression against a subject string: see the partial matching section for more details.

The match options are a set of one or more QRegularExpression::MatchOption values. They change the way a specific match of a regular expression against a subject string is done. Please refer to the QRegularExpression::MatchOption enum documentation for more details.

### Normal Matching

In order to perform a match you can simply invoke the match() function passing a string to match against. We refer to this string as the subject string. The result of the match() function is a QRegularExpressionMatch object that can be used to inspect the results of the match. For instance:

      // match two digits followed by a space and a word
      QRegularExpression re("\\d\\d \\w+");
      QRegularExpressionMatch match = re.match("abc123 def");
      bool hasMatch = match.hasMatch(); // true

If a match is successful, the (implicit) capturing group number 0 can be used to retrieve the substring matched by the entire pattern (see also the section about extracting captured substrings):

      QRegularExpression re("\\d\\d \\w+");
      QRegularExpressionMatch match = re.match("abc123 def");
      if (match.hasMatch()) {
          QString matched = match.captured(0); // matched == "23 def"
          // ...
      }

It's also possible to start a match at an arbitrary offset inside the subject string by passing the offset as an argument of the match() function. In the following example `"12 abc"` is not matched because the match is started at offset 1:

      QRegularExpression re("\\d\\d \\w+");
      QRegularExpressionMatch match = re.match("12 abc 45 def", 1);
      if (match.hasMatch()) {
          QString matched = match.captured(0); // matched == "45 def"
          // ...
      }

#### Extracting captured substrings

The QRegularExpressionMatch object contains also information about the substrings captured by the capturing groups in the pattern string. The captured() function will return the string captured by the n-th capturing group:

      QRegularExpression re("^(\\d\\d)/(\\d\\d)/(\\d\\d\\d\\d)$");
      QRegularExpressionMatch match = re.match("08/12/1985");
      if (match.hasMatch()) {
          QString day = match.captured(1); // day == "08"
          QString month = match.captured(2); // month == "12"
          QString year = match.captured(3); // year == "1985"
          // ...
      }

Capturing groups in the pattern are numbered starting from 1, and the implicit capturing group 0 is used to capture the substring that matched the entire pattern.

It's also possible to retrieve the starting and the ending offsets (inside the subject string) of each captured substring, by using the capturedStart() and the capturedEnd() functions:

      QRegularExpression re("abc(\\d+)def");
      QRegularExpressionMatch match = re.match("XYZabc123defXYZ");
      if (match.hasMatch()) {
          int startOffset = match.capturedStart(1); // startOffset == 6
          int endOffset = match.capturedEnd(1); // endOffset == 9
          // ...
      }

All of these functions have an overload taking a QString as a parameter in order to extract named captured substrings. For instance:

      QRegularExpression re("^(?<date>\\d\\d)/(?<month>\\d\\d)/(?<year>\\d\\d\\d\\d)$");
      QRegularExpressionMatch match = re.match("08/12/1985");
      if (match.hasMatch()) {
          QString date = match.captured("date"); // date == "08"
          QString month = match.captured("month"); // month == "12"
          QString year = match.captured("year"); // year == 1985
      }

### Global Matching

Global matching is useful to find all the occurrences of a given regular expression inside a subject string. Suppose that we want to extract all the words from a given string, where a word is a substring matching the pattern `\w+`.

QRegularExpression::globalMatch returns a QRegularExpressionMatchIterator, which is a Java-like forward iterator that can be used to iterate over the results. For instance:

      QRegularExpression re("(\\w+)");
      QRegularExpressionMatchIterator i = re.globalMatch("the quick fox");

Since it's a Java-like iterator, the QRegularExpressionMatchIterator will point immediately before the first result. Every result is returned as a QRegularExpressionMatch object. The hasNext() function will return true if there's at least one more result, and next() will return the next result and advance the iterator. Continuing from the previous example:

      QStringList words;
      while (i.hasNext()) {
          QRegularExpressionMatch match = i.next();
          QString word = match.captured(1);
          words << word;
      }
      // words contains "the", "quick", "fox"

You can also use peekNext() to get the next result without advancing the iterator.

It is possible to pass a starting offset and one or more match options to the globalMatch() function, exactly like normal matching with match().

### Partial Matching

A partial match is obtained when the end of the subject string is reached, but more characters are needed to successfully complete the match. Note that a partial match is usually much more inefficient than a normal match because many optimizations of the matching algorithm cannot be employed.

A partial match must be explicitly requested by specifying a match type of PartialPreferCompleteMatch or PartialPreferFirstMatch when calling QRegularExpression::match or QRegularExpression::globalMatch. If a partial match is found, then calling the hasMatch() function on the QRegularExpressionMatch object returned by match() will return `false`, but hasPartialMatch() will return `true`.

When a partial match is found, no captured substrings are returned, and the (implicit) capturing group 0 corresponding to the whole match captures the partially matched substring of the subject string.

Note that asking for a partial match can still lead to a complete match, if one is found; in this case, hasMatch() will return `true` and hasPartialMatch() `false`. It never happens that a QRegularExpressionMatch reports both a partial and a complete match.

Partial matching is mainly useful in two scenarios: validating user input in real time and incremental/multi-segment matching.

#### Validating user input

Suppose that we would like the user to input a date in a specific format, for instance "MMM dd, yyyy". We can check the input validity with a pattern like:

`^(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) \d\d?, \d\d\d\d$`

(This pattern doesn't catch invalid days, but let's keep it for the example's purposes).

We would like to validate the input with this regular expression while the user is typing it, so that we can report an error in the input as soon as it is committed (for instance, the user typed the wrong key). In order to do so we must distinguish three cases:

- the input cannot possibly match the regular expression;
- the input does match the regular expression;
- the input does not match the regular expression right now, but it will if more characters will be added to it.

Note that these three cases represent exactly the possible states of a QValidator (see the QValidator::State enum).

In particular, in the last case we want the regular expression engine to report a partial match: we are successfully matching the pattern against the subject string but the matching cannot continue because the end of the subject is encountered. Notice, however, that the matching algorithm should continue and try all possibilities, and in case a complete (non-partial) match is found, then this one should be reported, and the input string accepted as fully valid.

This behaviour is implemented by the PartialPreferCompleteMatch match type. For instance:

      QString pattern("^(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) \\d\\d?, \\d\\d\\d\\d$");
      QRegularExpression re(pattern);

      QString input("Jan 21,");
      QRegularExpressionMatch match = re.match(input, 0, QRegularExpression::PartialPreferCompleteMatch);
      bool hasMatch = match.hasMatch(); // false
      bool hasPartialMatch = match.hasPartialMatch(); // true

If matching the same regular expression against the subject string leads to a complete match, it is reported as usual:

      QString input("Dec 8, 1985");
      QRegularExpressionMatch match = re.match(input, 0, QRegularExpression::PartialPreferCompleteMatch);
      bool hasMatch = match.hasMatch(); // true
      bool hasPartialMatch = match.hasPartialMatch(); // false

Another example with a different pattern, showing the behaviour of preferring a complete match over a partial one:

      QRegularExpression re("abc\\w+X|def");
      QRegularExpressionMatch match = re.match("abcdef", 0, QRegularExpression::PartialPreferCompleteMatch);
      bool hasMatch = match.hasMatch(); // true
      bool hasPartialMatch = match.hasPartialMatch(); // false
      QString captured = match.captured(0); // captured == "def"

In this case, the subpattern `abc\\w+X` partially matches the subject string; however, the subpattern `def` matches the subject string completely, and therefore a complete match is reported.

If multiple partial matches are found when matching (but no complete match), then the QRegularExpressionMatch object will report the first one that is found. For instance:

      QRegularExpression re("abc\\w+X|defY");
      QRegularExpressionMatch match = re.match("abcdef", 0, QRegularExpression::PartialPreferCompleteMatch);
      bool hasMatch = match.hasMatch(); // false
      bool hasPartialMatch = match.hasPartialMatch(); // true
      QString captured = match.captured(0); // captured == "abcdef"

#### Incremental/multi-segment matching

Incremental matching is another use case of partial matching. Suppose that we want to find the occurrences of a regular expression inside a large text (that is, substrings matching the regular expression). In order to do so we would like to "feed" the large text to the regular expression engines in smaller chunks. The obvious problem is what happens if the substring that matches the regular expression spans across two or more chunks.

In this case, the regular expression engine should report a partial match, so that we can match again adding new data and (eventually) get a complete match. This implies that the regular expression engine may assume that there are other characters beyond the end of the subject string. This is not to be taken literally -- the engine will never try to access any character after the last one in the subject.

QRegularExpression implements this behaviour when using the PartialPreferFirstMatch match type. This match type reports a partial match as soon as it is found, and other match alternatives are not tried (even if they could lead to a complete match). For instance:

      QRegularExpression re("abc|ab");
      QRegularExpressionMatch match = re.match("ab", 0, QRegularExpression::PartialPreferFirstMatch);
      bool hasMatch = match.hasMatch(); // false
      bool hasPartialMatch = match.hasPartialMatch(); // true

This happens because when matching the first branch of the alternation operator a partial match is found, and therefore matching stops, without trying the second branch. Another example:

      QRegularExpression re("abc(def)?");
      QRegularExpressionMatch match = re.match("abc", 0, QRegularExpression::PartialPreferFirstMatch);
      bool hasMatch = match.hasMatch(); // false
      bool hasPartialMatch = match.hasPartialMatch(); // true

This shows what could seem a counterintuitve behaviour of quantifiers: since `?` is greedy, then the engine tries first to continue the match after having matched `"abc"`; but then the matching reaches the end of the subject string, and therefore a partial match is reported. This is even more surprising in the following example:

      QRegularExpression re("(abc)*");
      QRegularExpressionMatch match = re.match("abc", 0, QRegularExpression::PartialPreferFirstMatch);
      bool hasMatch = match.hasMatch(); // false
      bool hasPartialMatch = match.hasPartialMatch(); // true

It's easy to understand this behaviour if we remember that the engine expects the subject string to be only a substring of the whole text we're looking for a match into (that is, how we said before, that the engine assumes that there are other characters beyond the end of the subject string).

Since the `*` quantifier is greedy, then reporting a complete match could be an error, because after the current subject `"abc"` there may be other occurrences of `"abc"`. For instance, the complete text could have been "abcabcX", and therefore the right match to report (in the complete text) would have been `"abcabc"`; by matching only against the leading `"abc"` we instead get a partial match.

### Error Handling

It is possible for a QRegularExpression object to be invalid because of syntax errors in the pattern string. The isValid() function will return true if the regular expression is valid, or false otherwise:

      QRegularExpression invalidRe("(unmatched|parenthesis");
      bool isValid = invalidRe.isValid(); // false

You can get more information about the specific error by calling the errorString() function; moreover, the patternErrorOffset() function will return the offset inside the pattern string

      QRegularExpression invalidRe("(unmatched|parenthesis");
      if (!invalidRe.isValid()) {
          QString errorString = invalidRe.errorString(); // errorString == "missing )"
          int errorOffset = invalidRe.patternErrorOffset(); // errorOffset == 22
          // ...
      }

If a match is attempted with an invalid QRegularExpression, then the returned QRegularExpressionMatch object will be invalid as well (that is, its isValid() function will return false). The same applies for attempting a global match.

### Unsupported Perl-compatible Regular Expressions Features

QRegularExpression does not support all the features available in Perl-compatible regular expressions. The most notable one is the fact that duplicated names for capturing groups are not supported, and using them can lead to undefined behaviour.

This may change in a future version of Qt.

### Notes for QRegExp Users

The QRegularExpression class introduced in Qt 5 is a big improvement upon QRegExp, in terms of APIs offered, supported pattern syntax and speed of execution. The biggest difference is that QRegularExpression simply holds a regular expression, and it's not modified when a match is requested. Instead, a QRegularExpressionMatch object is returned, in order to check the result of a match and extract the captured substring. The same applies with global matching and QRegularExpressionMatchIterator.

Other differences are outlined below.

#### Exact matching

QRegExp::exactMatch() in Qt 4 served two purposes: it exactly matched a regular expression against a subject string, and it implemented partial matching. In fact, if an exact match was not found, one could still find out how much of the subject string was matched by the regular expression by calling QRegExp::matchedLength(). If the returned length was equal to the subject string's length, then one could desume that a partial match was found.

QRegularExpression supports partial matching explicitly by means of the appropriate MatchType. If instead you simply want to be sure that the subject string matches the regular expression exactly, you can wrap the pattern between a couple of anchoring expressions. Simply putting the pattern between the `^` and the `$` anchors is enough in most cases:

      QRegularExpression re("^this pattern must match exactly$");

However, remember that the `$` anchor not only matches at the end of the string, but also at a newline character right before the end of the string; that is, the previous pattern matches against the string "this pattern must match exactly\n". Also, the behaviour of both the `^` and the `$` anchors changes if the MultiLineOption is set either explicitly (as a pattern option) or implicitly (as a directive inside the pattern string).

Therefore, in the most general case, you should wrap the pattern between the `\A` and the `\z` anchors:

      QString p("a .*|pattern");
      QRegularExpression re("\\A(?:" + p + ")\\z"); // re matches exactly the pattern string p

Note the usage of the non-capturing group in order to preserve the meaning of the branch operator inside the pattern.

#### Global matching

Due to limitations of the QRegExp API it was impossible to implement global matching correctly (that is, like Perl does). In particular, patterns that can match 0 characters (like `"a*"`) are problematic.

QRegularExpression::globalMatch() implements Perl global match correctly, and the returned iterator can be used to examine each result.

#### Unicode properties support

When using QRegExp, character classes such as `\w`, `\d`, etc. match characters with the corresponding Unicode property: for instance, `\d` matches any character with the Unicode Nd (decimal digit) property.

Those character classes only match ASCII characters by default when using QRegularExpression: for instance, `\d` matches exactly a character in the `0-9` ASCII range. It is possible to change this behaviour by using the UseUnicodePropertiesOption pattern option.

#### Wildcard matching

There is no equivalent of wildcard matching in QRegularExpression. Nevertheless, rewriting a regular expression in wildcard syntax to a Perl-compatible regular expression is a very easy task, given the fact that wildcard syntax supported by QRegExp is very simple.

#### Other pattern syntaxes

QRegularExpression supports only Perl-compatible regular expressions.

#### Minimal matching

QRegExp::setMinimal() implemented minimal matching by simply reversing the greediness of the quantifiers (QRegExp did not support lazy quantifiers, like `*?`, `+?`, etc.). QRegularExpression instead does support greedy, lazy and possessive quantifiers. The InvertedGreedinessOption pattern option can be useful to emulate the effects of QRegExp::setMinimal(): if enabled, it inverts the greediness of quantifiers (greedy ones become lazy and vice versa).

#### Caret modes

The AnchoredMatchOption match option can be used to emulate the QRegExp::CaretAtOffset behaviour. There is no equivalent for the other QRegExp::CaretMode modes.

### Debugging Code that Uses QRegularExpression

QRegularExpression internally uses a just in time compiler (JIT) to optimize the execution of the matching algorithm. The JIT makes extensive usage of self-modifying code, which can lead debugging tools such as Valgrind to crash. You must enable all checks for self-modifying code if you want to debug programs using QRegularExpression (f.i., see Valgrind's `--smc-check` command line option). The downside of enabling such checks is that your program will run considerably slower.

To avoid that, the JIT is disabled by default if you compile Qt in debug mode. It is possible to override the default and enable or disable the JIT usage (both in debug or release mode) by setting the `QT_ENABLE_REGEXP_JIT` environment variable to a non-zero or zero value respectively.

See also QRegularExpressionMatch and QRegularExpressionMatchIterator.

## Member Type Documentation

### enum QRegularExpression::MatchOption
flags QRegularExpression::MatchOptions

Constant | Value | Description
--- | --- | ---
`QRegularExpression::NoMatchOption` | `0x0000` | No match options are set.
`QRegularExpression::AnchoredMatchOption` | `0x0001` | The match is constrained to start exactly at the offset passed to match() in order to be successful, even if the pattern string does not contain any metacharacter that anchors the match at that point.
`QRegularExpression::DontCheckSubjectStringMatchOption` | `0x0002` | The subject string is not checked for UTF-16 validity before attempting a match. Use this option with extreme caution, as attempting to match an invalid string may crash the program and/or constitute a security issue. This enum value has been introduced in Qt 5.4.

The MatchOptions type is a typedef for QFlags<MatchOption>. It stores an OR combination of MatchOption values.

### enum QRegularExpression::MatchType

The MatchType enum defines the type of the match that should be attempted against the subject string.

Constant | Value | Description
--- | --- | ---
`QRegularExpression::NormalMatch` | `0` | A normal match is done.
`QRegularExpression::PartialPreferCompleteMatch` | `1` | The pattern string is matched partially against the subject string. If a partial match is found, then it is recorded, and other matching alternatives are tried as usual. If a complete match is then found, then it's preferred to the partial match; in this case only the complete match is reported. If instead no complete match is found (but only the partial one), then the partial one is reported.
`QRegularExpression::PartialPreferFirstMatch` | `2` | The pattern string is matched partially against the subject string. If a partial match is found, then matching stops and the partial match is reported. In this case, other matching alternatives (potentially leading to a complete match) are not tried. Moreover, this match type assumes that the subject string only a substring of a larger text, and that (in this text) there are other characters beyond the end of the subject string. This can lead to surprising results; see the discussion in the partial matching section for more details.
`QRegularExpression::NoMatch` | `3` | No matching is done. This value is returned as the match type by a default constructed QRegularExpressionMatch or QRegularExpressionMatchIterator. Using this match type is not very useful for the user, as no matching ever happens. This enum value has been introduced in Qt 5.1.

### enum QRegularExpression::PatternOption
flags QRegularExpression::PatternOptions

The PatternOption enum defines modifiers to the way the pattern string should be interpreted, and therefore the way the pattern matches against a subject string.

Constant | Value | Description
--- | --- | ---
`QRegularExpression::NoPatternOption` | `0x0000` | No pattern options are set.
`QRegularExpression::CaseInsensitiveOption` | `0x0001` | The pattern should match against the subject string in a case insensitive way. This option corresponds to the /i modifier in Perl regular expressions.
`QRegularExpression::DotMatchesEverythingOption` | `0x0002` | The dot metacharacter (`.`) in the pattern string is allowed to match any character in the subject string, including newlines (normally, the dot does not match newlines). This option corresponds to the `/s` modifier in Perl regular expressions.
`QRegularExpression::MultilineOption` | `0x0004` | The caret (`^`) and the dollar (`$`) metacharacters in the pattern string are allowed to match, respectively, immediately after and immediately before any newline in the subject string, as well as at the very beginning and at the very end of the subject string. This option corresponds to the `/m` modifier in Perl regular expressions.
`QRegularExpression::ExtendedPatternSyntaxOption` | `0x0008` | Any whitespace in the pattern string which is not escaped and outside a character class is ignored. Moreover, an unescaped sharp (#) outside a character class causes all the following characters, until the first newline (included), to be ignored. This can be used to increase the readability of a pattern string as well as put comments inside regular expressions; this is particulary useful if the pattern string is loaded from a file or written by the user, because in C++ code it is always possible to use the rules for string literals to put comments outside the pattern string. This option corresponds to the `/x` modifier in Perl regular expressions.
`QRegularExpression::InvertedGreedinessOption` | `0x0010` | The greediness of the quantifiers is inverted: `*`, `+`, `?`, `{m,n}`, etc. become lazy, while their lazy versions (`*?`, `+?`, `??`, `{m,n}?`, etc.) become greedy. There is no equivalent for this option in Perl regular expressions.
`QRegularExpression::DontCaptureOption` | `0x0020` | The non-named capturing groups do not capture substrings; named capturing groups still work as intended, as well as the implicit capturing group number 0 corresponding to the entire match. There is no equivalent for this option in Perl regular expressions.
`QRegularExpression::UseUnicodePropertiesOption` | `0x0040` | The meaning of the `\w`, `\d`, etc., character classes, as well as the meaning of their counterparts (`\W`, `\D`, etc.), is changed from matching ASCII characters only to matching any character with the corresponding Unicode property. For instance, `\d` is changed to match any character with the Unicode Nd (decimal digit) property; `\w` to match any character with either the Unicode L (letter) or N (digit) property, plus underscore, and so on. This option corresponds to the `/u` modifier in Perl regular expressions.
`QRegularExpression::OptimizeOnFirstUsageOption` | `0x0080` | The regular expression will be optimized (and possibly JIT-compiled) on its first usage, instead of after a certain (undefined) number of usages. See also optimize(). This enum value has been introduced in Qt 5.4.
`QRegularExpression::DontAutomaticallyOptimizeOption` | `0x0100` | Regular expressions are automatically optimized after a certain number of usages; setting this option prevents such optimizations, therefore avoiding possible unpredictable spikes in CPU and memory usage. If both this option and the `OptimizeOnFirstUsageOption` option are set, then this option takes precedence. Note: this option will still let the regular expression to be optimized by manually calling optimize(). This enum value has been introduced in Qt 5.4.

The PatternOptions type is a typedef for QFlags<PatternOption>. It stores an OR combination of PatternOption values.

## Member Function Documentation

### QRegularExpression::QRegularExpression()

Constructs a QRegularExpression object with an empty pattern and no pattern options.

See also setPattern() and setPatternOptions().

### QRegularExpression::QRegularExpression(const QString &pattern, PatternOptions options = NoPatternOption)

Constructs a QRegularExpression object using the given pattern as pattern and the options as the pattern options.

See also setPattern() and setPatternOptions().

### QRegularExpression::QRegularExpression(const QRegularExpression &re)

Constructs a QRegularExpression object as a copy of re.

See also operator=().

### QRegularExpression::~QRegularExpression()

Destroys the QRegularExpression object.

### int QRegularExpression::captureCount() const

Returns the number of capturing groups inside the pattern string, or -1 if the regular expression is not valid.

Note: The implicit capturing group 0 is not included in the returned number.

See also isValid().

### QString QRegularExpression::errorString() const

Returns a textual description of the error found when checking the validity of the regular expression, or "no error" if no error was found.

See also isValid() and patternErrorOffset().

### `[static]` QString QRegularExpression::escape(const QString &str)

Escapes all characters of str so that they no longer have any special meaning when used as a regular expression pattern string, and returns the escaped string. For instance:

      QString escaped = QRegularExpression::escape("a(x) = f(x) + g(x)");
      // escaped == "a\\(x\\)\\ \\=\\ f\\(x\\)\\ \\+\\ g\\(x\\)"

This is very convenient in order to build patterns from arbitrary strings:

      QString pattern = "(" + QRegularExpression::escape(name) +
                        "|" + QRegularExpression::escape(nickname) + ")";
      QRegularExpression re(pattern);

Note: This function implements Perl's quotemeta algorithm and escapes with a backslash all characters in str, except for the characters in the `[A-Z]`, `[a-z]` and `[0-9]` ranges, as well as the underscore (`_`) character. The only difference with Perl is that a literal NUL inside str is escaped with the sequence `"\\0"` (backslash + `'0'`), instead of `"\\\0"` (backslash + `NUL`).

### QRegularExpressionMatchIterator QRegularExpression::globalMatch(const QString &subject, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const

Attempts to perform a global match of the regular expression against the given subject string, starting at the position offset inside the subject, using a match of type matchType and honoring the given matchOptions.

The returned QRegularExpressionMatchIterator is positioned before the first match result (if any).

See also QRegularExpressionMatchIterator and global matching.

### QRegularExpressionMatchIterator QRegularExpression::globalMatch(const QStringRef &subjectRef, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const

This is an overloaded function.

Attempts to perform a global match of the regular expression against the given subjectRef string reference, starting at the position offset inside the subject, using a match of type matchType and honoring the given matchOptions.

The returned QRegularExpressionMatchIterator is positioned before the first match result (if any).

This function was introduced in Qt 5.5.

See also QRegularExpressionMatchIterator and global matching.

### bool QRegularExpression::isValid() const

Returns `true` if the regular expression is a valid regular expression (that is, it contains no syntax errors, etc.), or false otherwise. Use errorString() to obtain a textual description of the error.

See also errorString() and patternErrorOffset().

### QRegularExpressionMatch QRegularExpression::match(const QString &subject, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const

Attempts to match the regular expression against the given subject string, starting at the position offset inside the subject, using a match of type matchType and honoring the given matchOptions.

The returned QRegularExpressionMatch object contains the results of the match.

See also QRegularExpressionMatch and normal matching.

### QRegularExpressionMatch QRegularExpression::match(const QStringRef &subjectRef, int offset = 0, MatchType matchType = NormalMatch, MatchOptions matchOptions = NoMatchOption) const

This is an overloaded function.

Attempts to match the regular expression against the given subjectRef string reference, starting at the position offset inside the subject, using a match of type matchType and honoring the given matchOptions.

The returned QRegularExpressionMatch object contains the results of the match.

This function was introduced in Qt 5.5.

See also QRegularExpressionMatch and normal matching.

### QStringList QRegularExpression::namedCaptureGroups() const

Returns a list of captureCount() + 1 elements, containing the names of the named capturing groups in the pattern string. The list is sorted such that the element of the list at position `i` is the name of the `i`-th capturing group, if it has a name, or an empty string if that capturing group is unnamed.

For instance, given the regular expression

      (?<day>\d\d)-(?<month>\d\d)-(?<year>\d\d\d\d) (\w+) (?<name>\w+)

namedCaptureGroups() will return the following list:

      ("", "day", "month", "year", "", "name")

which corresponds to the fact that the capturing group #0 (corresponding to the whole match) has no name, the capturing group #1 has name "day", the capturing group #2 has name "month", etc.

If the regular expression is not valid, returns an empty list.

This function was introduced in Qt 5.1.

See also isValid(), QRegularExpressionMatch::captured(), and QString::isEmpty().

### void QRegularExpression::optimize() const

Forces an immediate optimization of the pattern, including JIT-compiling it (if the JIT compiler is enabled).

Patterns are normally optimized only after a certain number of usages. If you can predict that this QRegularExpression object is going to be used for several matches, it may be convenient to optimize it in advance by calling this function.

This function was introduced in Qt 5.4.

See also QRegularExpression::OptimizeOnFirstUsageOption.

### QString QRegularExpression::pattern() const

Returns the pattern string of the regular expression.

See also setPattern() and patternOptions().

### int QRegularExpression::patternErrorOffset() const

Returns the offset, inside the pattern string, at which an error was found when checking the validity of the regular expression. If no error was found, then -1 is returned.

See also pattern(), isValid(), and errorString().

### PatternOptions QRegularExpression::patternOptions() const

Returns the pattern options for the regular expression.

See also setPatternOptions() and pattern().

### void QRegularExpression::setPattern(const QString &pattern)

Sets the pattern string of the regular expression to pattern. The pattern options are left unchanged.

See also pattern() and setPatternOptions().

### void QRegularExpression::setPatternOptions(PatternOptions options)

Sets the given options as the pattern options of the regular expression. The pattern string is left unchanged.

See also patternOptions() and setPattern().

### void QRegularExpression::swap(QRegularExpression &other)

Swaps the regular expression other with this regular expression. This operation is very fast and never fails.

### bool QRegularExpression::operator!=(const QRegularExpression &re) const

Returns `true` if the regular expression is different from re, or false otherwise.

See also operator==().

### QRegularExpression &QRegularExpression::operator=(const QRegularExpression &re)

Assigns the regular expression re to this object, and returns a reference to the copy. Both the pattern and the pattern options are copied.

### QRegularExpression &QRegularExpression::operator=(QRegularExpression &&re)

Move-assigns the regular expression re to this object, and returns a reference to the copy. Both the pattern and the pattern options are copied.

### bool QRegularExpression::operator==(const QRegularExpression &re) const

Returns `true` if the regular expression is equal to re, or false otherwise. Two QRegularExpression objects are equal if they have the same pattern string and the same pattern options.

See also operator!=().

## Related Non-Members

### uint qHash(const QRegularExpression &key, uint seed = 0)

Returns the hash value for key, using seed to seed the calculation.

This function was introduced in Qt 5.6.

### QDataStream &operator<<(QDataStream &out, const QRegularExpression &re)

Writes the regular expression re to stream out.

See also Serializing Qt Data Types.

### QDebug operator<<(QDebug debug, const QRegularExpression &re)

Writes the regular expression re into the debug object debug for debugging purposes.

See also Debugging Techniques.

### QDebug operator<<(QDebug debug, QRegularExpression::PatternOptions patternOptions)

Writes the pattern options patternOptions into the debug object debug for debugging purposes.

See also Debugging Techniques.

### QDataStream &operator>>(QDataStream &in, QRegularExpression &re)

Reads a regular expression from stream in into re.

See also Serializing Qt Data Types.