I'm working with a HTTP library (winhttp) for 2 weeks now and now I want to improve my RegExp's for retrieving some data on the target website.
Given the following HTML code:
Total Posts:</span> 22,423</li>
Now what I want to do is retrieving only the number and storing it into a variable:
regex = "Total Posts:</span> \\S+";
if(std::regex_search(regexs, regexmatch, regex))
{
temp = regexmatch[0];
found = temp.find(",");
if(found != std::string::npos)
temp.erase(found, 1);
temp.erase(0, 19);
temp.erase(temp.end() - 5, temp.end());
User._Posts = ConvertStringToInteger(temp);
}
Used some RegExp for this and stripping the parts off since I don't get how I only retrieve the pattern, not the whole result. Hopefully someone understands me. Already looked up the docs but found nothing what could help me.
To only match your desired pattern, you're wanting to use a capture group with std::regex_search.
Capture groups are meant for capturing matched regions within a regular expression and each captured region is represented by a sub_match. You can use the smatch specialization of match_results for working with string sub matches and then use the operator [] to get the match.
Example:
const std::string foo = "Total Posts:</span> 22,423</li>";
std::regex rgx("Total Posts:</span> ([^<]+)");
std::smatch match;
if (std::regex_search(foo.begin(), foo.end(), match, rgx)) {
std::cout << match[1] << '\n';
}
Output:
22,423
Related
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 want to split the following string around +, but I couldn't succeed in getting the correct regex for this.
String input = "SOP3a'+bEOP3'+SOP3b'+aEOP3'";
I want to have a result like this
[SOP3a'+bEOP3', SOP3b'+aEOP3']
In some cases I may have the following string
c+SOP2SOP3a'+bEOP3'+SOP3b'+aEOP3'EOP2
which should be split as
[c, SOP2SOP3a'+bEOP3'+SOP3b'+aEOP3'EOP2]
I have tried the following regex but it doesn't work.
input.split("(SOP[0-9](.*)EOP[0-9])*\\+((SOP)[0-9](.*)(EOP)[0-9])*");
Any help or suggestions are appreciated.
Thanks
You can use the following regex to match the string and by replacing it using captured group you can get the expected result :
(?m)(.*?)\+(SOP.*?$)
see demo / explanation
Following is the code in Java that would work for you:
public static void main(String[] args) {
String input = "SOP3a'+bEOP3'+SOP3b'+aEOP3'";
String pattern = "(?m)(.*?)\\+(SOP.*?$)";
Pattern regex = Pattern.compile(pattern);
Matcher m = regex.matcher(input);
if (m.find()) {
System.out.println("Found value: " + m.group(0));
System.out.println("Found value: " + m.group(1));
System.out.println("Found value: " + m.group(2));
} else {
System.out.println("NO MATCH");
}
}
The m.group(1) and m.group(2) are the values that you are looking for.
Do you really need to use split method?
And what are the rules? They are unclear to me.
Anyway, considering the regex you provided, I've only removed some unnecessary groups and I've found what you are looking for, however, instead of split, I just joined the matches as splitting it would generate some empty elements.
const str = "SOP1a+bEOP1+SOP2SOP3a'+bEOP3'+SOP3b'+aEOP3'EOP2";
const regex = RegExp(/(SOP[0-9].*EOP[0-9])*\+(SOP[0-9].*EOP[0-9])*/)
const matches = str.match(regex);
console.log('Matches ', matches);
console.log([matches[1],matches[2]]);
I'm currently trying to make a regex which matches URL parameters and extracts them.
For example, if I got the following parameters string ?param1=someValue¶m2=someOtherValue, std::regex_match should extract the following contents:
param1
some_content
param2
some_other_content
After trying different regex patterns, I finally built one corresponding to what I want: std::regex("(?:[\\?&]([^=&]+)=([^=&]+))*").
If I take the previous example, std::regex_match matches as expected. However, it does not extract the expected values, keeping only the last captured values.
For example, the following code:
std::regex paramsRegex("(?:[\\?&]([^=&]+)=([^=&]+))*");
std::string arg = "?param1=someValue¶m2=someOtherValue";
std::smatch sm;
std::regex_match(arg, sm, paramsRegex);
for (const auto &match : sm)
std::cout << match << std::endl;
will give the following output:
param2
someOtherValue
As you can see, param1 and its value are skipped and not captured.
After searching on google, I've found that this is due to greedy capture and I have modified my regex into "(?:[\\?&]([^=&]+)=([^=&]+))\\*?" in order to enable non-greedy capturing.
This regex works well when I try it on rubular but it does not match when I use it in C++ (std::regex_match returns false and nothing is captured).
I've tried different std::regex_constants options (different regex grammar by using std::regex_constants::grep, std::regex_constants::egrep, ...) but the result is the same.
Does someone know how to do non-greedy regex capture in C++?
As Casimir et Hippolyte explained in his comment, I just need to:
remove the quantifier
Use std::regex_iterator
It gives me the following code:
std::regex paramsRegex("[\\?&]([^=]+)=([^&]+)");
std::string url_params = "?key1=val1&key2=val2&key3=val3&key4=val4";
std::smatch sm;
auto params_it = std::sregex_iterator(url_params.cbegin(), url_params.cend(), paramsRegex);
auto params_end = std::sregex_iterator();
while (params_it != params_end) {
auto param = params_it->str();
std::regex_match(param, sm, paramsRegex);
for (const auto &s : sm)
std::cout << s << std::endl;
++params_it;
}
And here is the output:
?key1=val1
key1
val1
&key2=val2
key2
val2
&key3=val3
key3
val3
&key4=val4
key4
val4
The orignal regex (?:[\\?&]([^=&]+)=([^=&]+))* was just changed into [\\?&]([^=]+)=([^&]+).
Then, by using std::sregex_iterator, I get an iterator on each matching groups (?key1=val1, &key2=val2, ...).
Finally, by calling std::regex_match on each sub-string, I can retrieve parameters values.
Try to use match_results::prefix/suffix:
string match_expression("your expression");
smatch result;
regex fnd(match_expression, regex_constants::icase);
while (regex_search(in_str, result, fnd, std::regex_constants::match_any))
{
for (size_t i = 1; i < result.size(); i++)
{
std::cout << result[i].str();
}
in_str = result.suffix();
}
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'm trying to understand the logic on the regex in c++
std::string s ("Ni Ni Ni NI");
std::regex e ("(Ni)");
std::smatch sm;
std::regex_search (s,sm,e);
std::cout << "string object with " << sm.size() << " matches\n";
This form shouldn't give me the number of substrings matching my pattern? Because it always give me 1 match and it says that the match is [Ni , Ni]; but i need it to find every single pattern; they should be 3 and like this [Ni][Ni][Ni]
The function std::regex_search only returns the results for the first match found in your string.
Here is a code, merged from yours and from cplusplus.com. The idea is to search for the first match, analyze it, and then start again using the rest of the string (that is to say, the sub-string that directly follows the match that was found, which can be retrieved thanks to match_results::suffix ).
Note that the regex has two capturing groups (Ni*) and ([^ ]*).
std::string s("the knights who say Niaaa and Niooo");
std::smatch m;
std::regex e("(Ni*)([^ ]*)");
while (std::regex_search(s, m, e))
{
for (auto x : m)
std::cout << x.str() << " ";
std::cout << std::endl;
s = m.suffix().str();
}
This gives the following output:
Niaaa Ni aaa
Niooo Ni ooo
As you can see, for every call to regex_search, we have the following information:
the content of the whole match,
the content of every capturing group.
Since we have two capturing groups, this gives us 3 strings for every regex_search.
EDIT: in your case if you want to retrieve every "Ni", all you need to do is to replace
std::regex e("(Ni*)([^ ]*)");
with
std::regex e("(Ni)");
You still need to iterate over your string, though.