I am parsing some strings. If I encounter something like "Foo(bar)", I want to extract "Foo" and "bar"
How do I do it using QRegExp?
First thing, if you are using Qt 5 then rather use QRegularExpression class
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.
Secondly, get a visual tool that helps when testing/defining regular expressions, I use an online website.
To get the "Foo" and "Bar" from your example, I can suggest the following pattern:
(\w+)\((\w+)\)
--------------
The above means:
(\w+) - Capture one or more word characters (capture group 1)
\( - followed by a opening brace
(\w+) - then capture one or more word characters (capture group 2)
\) - followed by a closing brace
This pattern must be escaped for direct usage in the Qt regular expression:
const QRegularExpression expression( "(\\w+)\\((\\w+)\\)" );
QRegularExpressionMatch match = expression.match( "Foo(bar)" );
if( match.hasMatch() ) {
qDebug() << "0: " << match.captured( 0 ); // 0 is the complete match
qDebug() << "1: " << match.captured( 1 ); // First capture group
qDebug() << "2: " << match.captured( 2 ); // Second capture group
}
Output is:
0: "Foo(bar)"
1: "Foo"
2: "bar"
See the pattern in action online here. Hover the mouse over the parts in the "Expression" box to see the explanations or over the "Text" part to see the result.
Related
I have a regex that look like this:
(?="(test)"\s*:\s*(".*?"|\[.*?]))
to match the value between "..." or [...]
Input
"test":"value0"
"test":["value1", "value2"]
Output
Group1 Group2
test value0
test "value1", "value2" // or - value1", "value2
I there any trick to ignore "" and [] and stick with two group, group1 and group2?
I tried (?="(test)"\s*:\s*(?="(.*?)"|\[(.*?)])) but this gives me 4 groups, which is not good for me.
You may use this conditional regex in PHP with branch reset group:
"(test)"\h*:\h*(?|"([^"]*)"|\[([^]]*)])
This will give you 2 capture groups in both the inputs with enclosing " or [...].
RegEx Demo
RegEx Details:
(?|..) is a branch reset group. Here Subpatterns declared within each alternative of this construct will start over from the same index
(?|"([^"]*)"|\[([^]]*)]) is if-then-else conditional subpatern which means if " is matched then use "([^"]*)" otherwise use \[([^]]*)] subpattern
You can use a pattern like
"(test)"\s*:\s*\K(?|"\K([^"]*)|\[\K([^]]*))
See the regex demo.
Details:
" - a " char
(test) - Group 1: test word
" - a " char
\s*:\s* - a colon enclosed with zero or more whitespaces
\K - match reset operator that clears the current overall match memory buffer (group value is still kept intact)
(?|"\K([^"]*)|\[\K([^]]*)) - a branch reset group:
"\K([^"]*) - matches a ", then discards it, and then captures into Group 2 zero or more chars other than "
| - or
\[\K([^]]*) - matches a [, then discards it, and then captures into Group 2 zero or more chars other than ]
In Java, you can't use \K and ?|, use capturing groups:
String s = "\"test\":[\"value1\", \"value2\"]";
Pattern pattern = Pattern.compile("\"(test)\"\\s*:\\s*(?:\"([^\"]*)|\\[([^\\]]*))");
Matcher matcher = pattern.matcher(s);
while (matcher.find()){
System.out.println("Key: " + matcher.group(1));
if (matcher.group(2) != null) {
System.out.println("Value: " + matcher.group(2));
} else {
System.out.println("Value: " + matcher.group(3));
}
}
See a Java demo.
Context. I'm developing a Lexer/Tokenizing engine, which would use regex as a backend. The lexer accepts rules, which define the token types/IDs, e.g.
<identifier> = "\\b\\w+\\b".
As I envision, to do the regex match-based tokenizing, all of the rules defined by regexes are enclosed in capturing groups, and all groups are separated by ORs.
When the matching is being executed, every match we produce must have an index of the capturing group it was matched to. We use these IDs to map the matches to token types.
So the problem of this question arises - how to get the ID of the group?
Similar question here, but it does not provide the solution to my specific problem.
Exactly my problem here, but it's in JS, and I need a C/C++ solution.
So let's say I've got a regex, made up of capturing groups separated by an OR:
(\\b[a-zA-Z]+\\b)|(\\b\\d+\\b)
which matches the the whole numbers or alpha-words.
My problem requires that the index of the capture group the regex submatch matched to could be known, e.g. when matching the string
foo bar 123
3 iterations will be done. The group indexes of the matches of every iteration would be 0 0 1, because the first two matches matched the first capturing group, and the last match matched the second capturing group.
I know that in standard std::regex library it's not entirely possible (regex_token_iterator is not a solution, because I don't need to skip any matches).
I don't have much knowledge about boost::regex or PCRE regex library.
What is the best way to accomplish this task? Which is the library and method to use?
You may use the sregex_iterator to get all matches, and once there is a match you may analyze the std::match_results structure and only grab the ID-1 value of the group that participated in the match (note only one group here will match, either the first one, or the second), which can be conveniently checked with the m[index].matched:
std::regex r(R"((\b[[:alpha:]]+\b)|(\b\d+\b))");
std::string s = "foo bar 123";
for(std::sregex_iterator i = std::sregex_iterator(s.begin(), s.end(), r);
i != std::sregex_iterator();
++i)
{
std::smatch m = *i;
std::cout << "Match value: " << m.str() << " at Position " << m.position() << '\n';
for(auto index = 1; index < m.size(); ++index ){
if (m[index].matched) {
std::cout << "Capture group ID: " << index-1 << std::endl;
break;
}
}
}
See the C++ demo. Output:
Match value: foo at Position 0
Capture group ID: 0
Match value: bar at Position 4
Capture group ID: 0
Match value: 123 at Position 8
Capture group ID: 1
Note that R"(...)" is a raw string literal, no need to double backslashes inside it.
Also, index is set to 1 at the start of the for loop because the 0th group is the whole match, but you want group IDs to be zero-based, that is why 1 is subtracted later.
I tried the following regex:
const static char * regex_string = "([a-zA-Z0-9]+).*";
void find_first(const std::string str);
int main(int argc, char ** argv)
{
find_first("0s7fg9078dfg09d78fg097dsfg7sdg\r\nfdfgdfg");
}
void find_first(const std::string str)
{
std::cout << str << std::endl;
std::regex rgx(regex_string);
std::smatch matcher;
if(std::regex_match(str, matcher, rgx))
{
std::cout << "Found : " << matcher.str(0) << std::endl;
} else {
std::cout << "Not found" << std::endl;
}
}
DEMO
I expected the regex will be completely correct and the group will be found. But it wasn't. Why? How can I match the line-break in c++ regex? In Java it works fine.
The dot in regex usually matches any character other than a newline std::ECMAScript syntax.
. not newline any character except line terminators (LF, CR, LS, PS).
0s7fg9078dfg09d78fg097dsfg7sdg\r\nfdfgdfg
[a-zA-Z0-9]+ matches until \r ↑___↑ .* would match from here
In many regex flavors there is a dotall flag available to make the dot also match newlines.
If not, there are workarounds in different languages such as [^] not nothing or [\S\s] any whitespace or non-whitespace together in a class wich results in any character including \n
regex_string = "([a-zA-Z0-9]+)[\\S\\s]*";
Or use optional line breaks: ([a-zA-Z0-9]+).*(?:\\r?\\n.*)* or ([a-zA-Z0-9]+)(?:.|\\r?\\n)*
See your updated demo
Update - Another idea worth mentioning: std::regex::extended
A <period> ( '.' ), when used outside a bracket expression, is an ERE that shall match any character in the supported character set except NUL.
std::regex rgx(regex_string, std::regex::extended);
See this demo at tio.run
You may try const static char * regex_string = "((.|\r\n)*)";
I hope It will help you.
I am using CTest and PROPERTIES PASS_REGULAR_EXPRESSION.
[\S\s]* did not work, but (.|\r|\n)* did.
This regex:
Function registered for ID 2 was called(.|\r|\n)*PASS
Matches:
Running test function: RegisterThreeDiffItemsTest04
ID 2 registered for callback
ID 4 registered for callback
ID 11 registered for callback
Function registered for ID 2 was called
ID 2 callback deregistered
ID 4 callback deregistered
ID 11 callback deregistered
Setup: PASS
Note: CMakeLists.txt needs to escape the backslashes:
SET (ANDPASS "(.|\\r|\\n)*PASS")
I'm trying to use a regex for group matching. I want to extract two strings from one big string.
The input string looks something like this:
tХB:Username!Username#Username.tcc.domain.com Connected
tХB:Username!Username#Username.tcc.domain.com WEBMSG #Username :this is a message
tХB:Username!Username#Username.tcc.domain.com Status: visible
The Username can be anything. Same goes for the end part this is a message.
What I want to do is extract the Username that comes after the pound sign #. Not from any other place in the string, since that can vary aswell. I also want to get the message from the string that comes after the semicolon :.
I tried that with the following regex. But it never outputs any results.
regex rgx("WEBMSG #([a-zA-Z0-9]) :(.*?)");
smatch matches;
for(size_t i=0; i<matches.size(); ++i) {
cout << "MATCH: " << matches[i] << endl;
}
I'm not getting any matches. What is wrong with my regex?
Your regular expression is incorrect because neither capture group does what you want. The first is looking to match a single character from the set [a-zA-Z0-9] followed by <space>:, which works for single character usernames, but nothing else. The second capture group will always be empty because you're looking for zero or more characters, but also specifying the match should not be greedy, which means a zero character match is a valid result.
Fixing both of these your regex becomes
std::regex rgx("WEBMSG #([a-zA-Z0-9]+) :(.*)");
But simply instantiating a regex and a match_results object does not produce matches, you need to apply a regex algorithm. Since you only want to match part of the input string the appropriate algorithm to use in this case is regex_search.
std::regex_search(s, matches, rgx);
Putting it all together
std::string s{R"(
tХB:Username!Username#Username.tcc.domain.com Connected
tХB:Username!Username#Username.tcc.domain.com WEBMSG #Username :this is a message
tХB:Username!Username#Username.tcc.domain.com Status: visible
)"};
std::regex rgx("WEBMSG #([a-zA-Z0-9]+) :(.*)");
std::smatch matches;
if(std::regex_search(s, matches, rgx)) {
std::cout << "Match found\n";
for (size_t i = 0; i < matches.size(); ++i) {
std::cout << i << ": '" << matches[i].str() << "'\n";
}
} else {
std::cout << "Match not found\n";
}
Live demo
"WEBMSG #([a-zA-Z0-9]) :(.*?)"
This regex will match only strings, which contain username of 1 character length and any message after semicolon, but second group will be always empty, because tries to find the less non-greedy match of any characters from 0 to unlimited.
This should work:
"WEBMSG #([a-zA-Z0-9]+) :(.*)"
I am working in Qt 5.2, and I have a piece of code that takes in a string and enters one of several if statements based on its format. One of the formats searched for is the letters "RCV", followed by a variable amount of numbers, a decimal, and then one more number. There can be more than one of these values in the line, separated by "|", for example it could one value like "RCV0123456.1" or mulitple values like "RCV12345.1|RCV678.9". Right now I am using QRegExp class to find this, like this:
QString value = "RCV000030249.2|RCV000035360.2"; //Note: real test value from my code
if(QRegExp("^[RCV\d+\.\d\|?]+$").exactMatch(value))
std::cout << ":D" << std::endl;
else
std::cout << ":(" << std::endl;
I want it to use the if statement, but it keeps going into the else statement. Is there something I'm doing wrong with the regular expression?
Your expression should be like #vahancho mentionet in a comment:
if(QRegExp("^[RCV\\d+\\.\\d\\|?]+$").exactMatch(value))
If you use C++11, then you can use its raw strings feature:
if(QRegExp(R"(^[RCV\d+\.\d\|?]+$)").exactMatch(value))
Aside from escaping the backslashes which others has mentioned in answers and comments,
There can be more than one of these values in the line, separated by "|", for example it could one value like "RCV0123456.1" or mulitple values like "RCV12345.1|RCV678.9".
[RCV\d+\.\d\|?] may not be doing what you expect. Perhaps you want () instead of []:
/^
[RCV\d+\.\d\|?]+ # More than one of characters from the list:
# R, C, V, a digit, a +, a dot, a digit, a |, a ?
$/x
/^
(
RCV\d+\.\d # RCV, some digits, a dot, followed by a digit
\|? # Optional: a |
)+ # Quantifier of one or more
$/x
Also, maybe you could revise the regex such that the optional | requires the group to be matched *again*:
/^
(RCV\d+\.\d) # RCV, some digits, a dot, followed by a digit
(
\|(?1) # A |, then match subpattern 1 (Above)
)+ # Quantifier of one or more
$/x
Check if only valid occurences in line with the addition to require an | starting second occurence (having your implementation would not require the | even with double quotes):
QString value = "RCV000030249.2|RCV000035360.2"; //Note: real test value from my code
if(QRegExp("^RCV\\d+\\.\\d(\\|RCV\\d+\\.\\d)*$").exactMatch(value))
std::cout << ":D" << std::endl;
else
std::cout << ":(" << std::endl;