[Solved] regex not working in qt

[ashishbansal]

Hello everyone,
I am trying to use regex in qt. I want to use regex for matching URLs. I am using this regex : http://regexr.com/3acbl
But I got warnings and it didn't work :
@
warning: unknown escape sequence: '/'
in QString regexp = "(http(s)?://.)?(www.)?[-a-zA-Z0-9@:%.+~#=]{2,256}.[a-z]{2,6}\b([-a-zA-Z0-9@:%+.~#?&//=]*)";
^
warning: unknown escape sequence: '/'
warning: unknown escape sequence: '.'
warning: unknown escape sequence: '+'
warning: unknown escape sequence: '.'
warning: unknown escape sequence: '+'
@

When I googled these, I got to know that c++ does not recognizes these as escape sequence and require one extra backslash "" there.
@
QString regexp = "(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%.\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%\+.~#?&//=]*)";
@
Although warnings went after using one extra backslash but it is still not matching URLs.

Regards,
Ashish Bansal

[koahnig]

It looks like you should have a look to the documentation of "QRegExp":http://doc.qt.io/qt-5/qregexp.html and "QRegularExpression":http://doc.qt.io/qt-5/qregularexpression.html or the "regexp example":http://doc.qt.io/qt-5/qtwidgets-tools-regexp-example.html

[SGaist]

Hi,

Out of curiosity, why the regexp ? Wouldn't QUrl be more adequate ?

[ashishbansal]

Hi SGaist,

I am not able to validate URI using QUrl::​isValid(). It does not checks the syntax of the URL. It just checks the encoding errors like if I my URL is
@
http://foo.bar/%3
@

It returns false and if URL is
@
foo://bar or foo://bar/baz
@

It returns true.

Then How can I use it to validate the URL?

[ashishbansal]

Hi koahnig,

Can you please explain it a bit?

EDIT:
@
The C++ compiler transforms backslashes in strings. To include a \ in a regexp, enter it twice, i.e. \. To match the backslash character itself, enter it four times, i.e. \\.
@

I already have corrected this. Then where's the mistake?

[koahnig]

[quote author="ashishbansal" date="1423288352"]Hi koahnig,

Can you please explain it a bit?

EDIT:
@
The C++ compiler transforms backslashes in strings. To include a \ in a regexp, enter it twice, i.e. \. To match the backslash character itself, enter it four times, i.e. \\.
@

I already have corrected this. Then where's the mistake?[/quote]

Your post requires quite a number of assumptions what you are trying to do.My impression was that you simply trying to store some syntax of regexp in a QString. However, you would need an engine such as QRegExp or QRegularExpressions.
There you should find also all things for C++ string handling.Therefore I thought that you should know about QRegExp.

[ashishbansal]

Well for the sake of simplicity, I hadn't posted the whole code. I am already using QRegExp in my code.
@
QString url = "http://foo.bar";

QString regexp = "(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%.\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%\+.~#?&//=]*)";

QRegExp rx(regexp);
rx.indexIn(url);

if(rx.cap(0).length() != 0){
//url passed validation test
....
}
@

[koahnig]

OK, sorry for my wrong assumption.

I would recommend the QRegExp example for checking, if you are not doing this already. I am using it for fast checks of reg exp.

I have tried with your example, but I could not verify any of your examples. The exampel gives you also the string with proper escape sequences for your code. However, I had to reverse your escapes. Probably there is the problem.

[SGaist]

"This":https://gist.github.com/dperini/729294 might interest you then

[ashishbansal]

[quote author="koahnig" date="1423307221"]OK, sorry for my wrong assumption.

I would recommend the QRegExp example for checking, if you are not doing this already. I am using it for fast checks of reg exp.

I have tried with your example, but I could not verify any of your examples. The exampel gives you also the string with proper escape sequences for your code. However, I had to reverse your escapes. Probably there is the problem.
[/quote]

Hey thanks for referring to that tool. Actually I missed one backslash on "\b" , that's why it was not working but that tool gave me correct escaped string on passing my normal js regex :)

[quote author="SGaist" date="1423344819"]"This":https://gist.github.com/dperini/729294 might interest you then[/quote]

Well that regex is most popular regex on the Google but I don't know why it does not work for me. You can check it here : http://regexr.com/3acgt
Anyway Thanks!

[In case someone needs regex for URL, you can try this out]
Finally I have used this basic regex for URL validation:
@
^(((http|ftp)(s?)://)|(www.))(([a-zA-Z0-9-.]+(.[a-zA-Z0-9-.]+)+)|localhost)(/?)([a-zA-Z0-9-.?,'/\+&%$#_])?([\d\w./%+-=&?:\"',|~;])$
@

Escaped Pattern for using it in C++:
@
"^(((http|ftp)(s?)\:\/\/)|(www\.))(([a-zA-Z0-9\-\.]+(\.[a-zA-Z0-9\-\.]+)+)|localhost)(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&%\$#_])?([\d\w\.\/\%\+\-\=\&\?\:\\\"\'\,\|\~\;])$"
@