I am doing a project with a Pascal subset. My code looks like:
NLINE [\n]
BRACKET ['('|')']
%%
{BRACKET} {
std::cout << "Found BRACKET symbol " << yytext[0] << std::endl;
return yytext[0];
}
{NLINE} {
std::cout << "Found NEWLINE symbol " << yytext[0] << std::endl;
yylineno++;
}
...
. { // anything is exactly before EOF
std::cout << "Found ANYTHING " << yytext[0] << std::endl;
yylval = NONE;
return yytext[0];
}
I tried many ways to deal with that, also just \n instead of [\n] or [ \n] but without the expected results. Below is the output:
...
Found BRACKET symbol )
Found ANYTHING ;
Found ANYTHING << where in code should be \n
I know that this is \n issue, because when I push the code without that it works like a charm!
Will appreciate every constructive answer.
The problem seemed to be the carriage return symbol. In case you will have similar issue, if this won't help, you should check other nonprintable characters.
In my case helped:
DELIM [ \t\r]
DELIM is "eated" in my solution so no rule is applied.
Related
I'm writing a module that's making some string substitutions into text to give to a scripting language. The language's syntax is vaugely lisp-y, so expressions are bounded by parentheses and symbols separated by spaces, most of them starting with '$'. A regular expression like this seems like it should give matches at the appropriate symbol boundaries:
auto re_match_abc = std::regex{ "(?=.*[[:space:]()])\\$abc(?=[()[:space:]].*)" };
But in my environment (Visual C++ 2017, 15.9.19, targetting C++-17) it can match strings without a suitable boundary in front of them:
std::cout << " $abc -> " << std::regex_replace(" $abc ", re_match_abc, "***") << std::endl;
std::cout << " ($abc) -> " << std::regex_replace("($abc)", re_match_abc, "***") << std::endl;
std::cout << "xyz$abc -> " << std::regex_replace("xyz$abc ", re_match_abc, "***") << std::endl;
std::cout << " $abcdef -> " << std::regex_replace(" $abcdef", re_match_abc, "***") << std::endl;
// Result from VC++ 2017:
//
// $abc -> ***
// ($abc) -> (***)
// xyz$abc -> xyz*** <= What's going wrong here?
// $abcdef -> $abcdef
Why is that regex ignoring the positive-lookahead requirement to have at least one space or parenthesis before the matching text?
[I realize that there are other ways to do this job and to do it really robustly maybe I should use something to turn the string into a token stream, but for the immediate job I have (and because the person authoring the strings that get processed is sitting next to me, so we can coordinate) I thought that regex replacements would do for now.]
You need to use a positive lookbehind instead. What you really want is this:
auto re_match_abc = std::regex{ "(?<=[[:space:]()])\\$abc(?=[()[:space:]])" };
You can try it out on a website like https://regex101.com/ (just remove the escaped backslash that's required for the C++ string). It explains what each piece of the regex is doing and shows you everything that matches.
Keep in mind that this will also match things like )$abc)
Edit: std::regex apparently does not support lookbehind. For you specific case you might try something like this:
auto re_match_abc = std::regex{ "([[:space:]()])\\$abc(?=[()[:space:]])" };
std::cout << " $abc -> " << std::regex_replace(" $abc ", re_match_abc, "$1***") << std::endl;
std::cout << " ($abc) -> " << std::regex_replace("($abc)", re_match_abc, "$1***") << std::endl;
std::cout << "xyz$abc -> " << std::regex_replace("xyz$abc ", re_match_abc, "$1***") << std::endl;
std::cout << " $abcdef -> " << std::regex_replace(" $abcdef", re_match_abc, "$1***") << std::endl;
output:
$abc -> ***
($abc) -> (***)
xyz$abc -> xyz$abc
$abcdef -> $abcdef
try it here
Here instead of a lookbehind we have a normal capture group. In the replacement we're emitting whatever we captured (a parenthesis or space) followed by the actual string we want to replace $abc with.
I suppose it's something very stupid, however this does not match, and I have no idea why.
I compiles successfully and everything, but it just doesn't match.
I've already used RE(".*") but it doesn't work as well.
The system is OS X (installed pcre using brew).
std::string s;
if (pcrecpp::RE("h.*o").FullMatch("hello", &s))
{
std::cout << "Successful match " << s << std::endl;
}
You are trying to extract one subpattern (in &s), but have not included any parentheses to capture that subpattern. Try this (untested, note parentheses).
std::string s;
if (pcrecpp::RE("(h.*o)").FullMatch("hello", &s))
{
std::cout << "Successful match " << s << std::endl;
}
The documentation at http://www.pcre.org/original/doc/html/pcrecpp.html has a similar example, stating:
Example: fails because there aren't enough sub-patterns:
!pcrecpp::RE("\w+:\d+").FullMatch("ruby:1234", &s);
I'm using boost regex_match and I have a problem with matching no tab characters.
My test application looks as follows:
#include <iostream>
#include <string>
#include <boost/spirit/include/classic_regex.hpp>
int
main(int args, char** argv)
{
boost::match_results<std::string::const_iterator> what;
if(args == 3) {
std::string text(argv[1]);
boost::regex expression(argv[2]);
std::cout << "Text : " << text << std::endl;
std::cout << "Regex: " << expression << std::endl;
if(boost::regex_match(text, what, expression, boost::match_default) != 0) {
int i = 0;
std::cout << text;
if(what[0].matched)
std::cout << " matches with regex pattern!" << std::endl;
else
std::cout << " does not match with regex pattern!" << std::endl;
for(boost::match_results<std::string::const_iterator>::const_iterator it=what.begin(); it!=what.end(); ++it) {
std::cout << "[" << (i++) << "] " << it->str() << std::endl;
}
} else {
std::cout << "Expression does not match!" << std::endl;
}
} else {
std::cout << "Usage: $> ./boost-regex <text> <regex>" << std::endl;
}
return 0;
}
If I run the program with these arguments, I don't get the expected result:
$> ./boost-regex "`cat file`" "(?=.*[^\t]).*"
Text : This text includes some tabulators
Regex: (?=.*[^\t]).*
This text includes some tabulators matches with regex pattern!
[0] This text includes some tabulators
In this case I would have expected that what[0].matched is false, but it's not.
Is there any mistake in my regular expression?
Or do I have to use other format/match flag?
Thank you in advance!
I am not sure what you want to do. My understanding is, you want the regex to fail as soon as there is a tab in the text.
Your positive lookahead assertion (?=.*[^\t]) is true as soon as it finds a non tab, and there are a lot of non tabs in your text.
If you want it to fail, when there is a tab, go the other way round and use a negative lookahead assertion.
(?!.*\t).*
this assertion will fail as soon as it find a tab.
I want to match every single number in the following string:
-0.237522264173E+01 0.110011117918E+01 0.563118085683E-01 0.540571836345E-01 -0.237680494785E+01 0.109394729137E+01 -0.237680494785E+01 0.109394729137E+01 0.392277532367E+02 0.478587433035E+02
However, for some reason the following boost::regex doesn't work:
(.*)(-?\\d+\\.\\d+E\\+\\d+ *){10}(.*)
What's wrong with it?
EDIT: posting relevant code:
std::ifstream plik("chains/peak-summary.txt");
std::string mystr((std::istreambuf_iterator<char>(plik)), std::istreambuf_iterator<char>());
plik.close();
boost::cmatch what;
boost::regex expression("(.*)(-?\\d+\\.\\d+E\\+\\d+ *){10}(.*)");
std::cout << "String to match against: \"" << mystr << "\"" << std::endl;
if(regex_match(mystr.c_str(), what, expression))
{
std::cout << "Match!";
std::cout << std::endl << what[0] << std::endl << what[1] << std::endl;
} else {
std::cout << "No match." << std::endl;
}
output:
String to match against: " -0.237555275450E+01 0.109397523269E+01 0.560420828508E-01 0.556732715285E-01 -0.237472295761E+01 0.110192835331E+01 -0.237472295761E+01 0.110192835331E+01 0.393040553508E+02 0.478540190640E+02
"
No match.
Also posting the contents of file read into the string:
[dare2be#schroedinger multinest-peak]$ cat chains/peak-summary.txt
-0.237555275450E+01 0.109397523269E+01 0.560420828508E-01 0.556732715285E-01 -0.237472295761E+01 0.110192835331E+01 -0.237472295761E+01 0.110192835331E+01 0.393040553508E+02 0.478540190640E+02
The (.*) around your regex match and consume all text at the start and end of the string, so if there are more than ten numbers, the first ones won't be matched.
Also, you're not allowing for negative exponents.
(-?\\d\\.\\d+E[+-]\\d+ *){10,}
should work.
This will match all of the numbers in a single string; if you want to match each number separately, you have to use (-?\\d\\.\\d+E[+-]\\d+) iteratively.
Try with:
(-?[0-9]+\\.[0-9]+E[+-][0-9]+)
Your (.*) in the beggining matches greedy whole string.
I am trying to use this expression:
Expression: "\w{1,}\s*?\-\-(\>)?\s*?\w{1,}"
Keep in mind I am escaping the \ with a second \ in my code.
When searching in the strings below. I think I am close, but no cigar. I want the expression above to be able to find matches in the text below. Where am I going wrong?
Text: "AB --> CD"
Text: "AB --> Z"
Text: "A --> 123d"
etc.
Resources Used:
http://www.solarix.ru/for_developers/api/regex-en.html
http://www.boost.org/doc/libs/1_47_0/libs/regex/doc/html/boost_regex/introduction_and_overview.html
http://www.regular-expressions.info/reference.html
UPDATE
The comment helped me. I would still like to see people post on my thread, for record keeping purposes, regex sites that have helped them master regex. Anyways my code (mostly copied from the boost website) is.
/* All captures from a regular expression */
#include <boost/regex.hpp>
#include <iostream>
/* Compiled with g++ -o regex_tut -lboost_regex -Wall ./regex_tut.cpp */
void print_captures(const std::string& regx, const std::string& text)
{
boost::regex e(regx);
boost::smatch what;
std::cout << "Expression: \"" << regx << "\"\n";
std::cout << "Text: \"" << text << "\"\n";
if(boost::regex_match(text, what, e, boost::match_extra))
{
unsigned i;
std::cout << "** Match found **\n Sub-Expressions:\n";
for(i = 0; i < what.size(); ++i) {
std::cout << " $" << i << " = \"" << what[i] << "\"\n";
}
}
else
{
std::cout << "** No Match found **\n";
}
}
int main(int argc, char* argv[ ])
{
print_captures("^\\w+\\s*-->?\\s*\\w+\\s*(\\(\\d+\\))?", "AB --> CD (12)" );
return 0;
}
Seems to work. Please though so I can accept an answer post your favorite site up and give a newb a few pointers =).
Not sure if i understood your question correctly, but if you want your regex to match for example AB and CD in "AB --> CD" you can use the following regex:
Expression: "(\w+)\s*-->?\s*(\w+)"