CODEWITHSUNDEEP
c++regex
Ammu S
Ammu S

Reputation: 11

how do i convert a c# style regular expression to c++ style

I was trying to parse a lengthy string through a regular expression, i tried doing it with the following RE and text mentioned at this link http://regexr.com/3a7uf

But when I try to parse the text in c++ using the same RE, the compile time warnings and output not as expected.

Please advise how to get this RE sorted into a format so that it becomes possible to parse text, in a C++ program.

The code goes like this: 

std::string str = "root     21015  0.0  0.0      0     0 ?        S    "
    "16:07   0:00 [kworker/5:0]\n            root     21095  0.0  0.0  "
    "    0     0 ?        S    16:08   0:00 [kworker/2:2]\n            "
    "root     21097  0.0  0.0      0     0 ?        S    16:08   0:00 ["
    "kworker/u16:4]\n            ashish   21103 17.1  1.2 591536 106056"
    " ?       Sl   16:12   0:01 /usr/lib/firefox/firefox";

std::regex firefox ("[0-9].\..*.firefox");

std::smatch sm;
std::regex_match (str, sm, firefox);
std::cout << "number of matches: " << sm.size() << std::endl;

std::cout << "matches were: " << std::endl;
for (unsigned int i = 0; i < sm.size(); i++)
{
    std::cout << "[" << sm[i] << "]";
}

warning during compilation as follows:

warning: unknown escape sequence: '\\.'
     regex firefox ("[0-9].\\..*.firefox");

output is as follows:

number of matches: 0

matches were:

Upvotes: 1

Views: 104

Answers (4)

Ammu S
Ammu S

Reputation: 11

Thanks for the replies. There was nothing wrong with the expression itself.

I just used the following syntax to create the regular expression and it worked well.

std::regex otherProcessRegEx ("[0-9][0-9][:.:].*.[a-z].|[0-9][:.:].*.[a-z]",
               std::regex_constants::ECMAScript |     
               std::regex_constants::icase);

with c++ 11 were introduced these http://www.johndcook.com/blog/cpp_regex/ different types of RegEx, which were needed to be specified.

:)

Upvotes: 0

Ehryk
Ehryk

Reputation: 1990

This looks to me to just be an issue with the way strings are dealt with. You can try

std::regex firefox (@"[0-9].\..*.firefox");

To indicate that it is a string literal, or if that syntax isn't supported try

std::regex firefox ("[0-9].\\..*.firefox");

Which is saying you really want a \ character in the string, not an escaped period.

Edit

From the comment below, it appears as though the C# syntax was not correct, or the periods were meant to concatenate (like PHP?), however they do not concatenate in regular expressions, they are placeholders.

std::regex firefox ("[0-9]+[.][0-9]+[^.]*firefox");

Could you highlight what you want to match, exactly (start to finish), in the sample above? I can't really tell where you want the matching to start, but if you're trying to find numbers and periods, the above would start at the 1.2.

Upvotes: 1

hwnd
hwnd

Reputation: 70732

You need to use double escapes here.

[0-9].\\..*.firefox

Upvotes: 3

adv12
adv12

Reputation: 8551

You're going to have to escape your backslashes for them to be valid C++ strings. For instance, try:

std::regex firefox ("[0-9].\\..*.firefox");

Upvotes: 1

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