Regex to replace all occurrences between two matches

Question

I am using std::regex and need to do a search and replace.

The string I have is:

begin foo even spaces and maybe new line(
some text only replace foo foo bar foo, keep the rest
)
some more text not replace foo here

Only the stuff between begin .... ( and ) should be touched.

I manage to replace the first foo by using this search and replace:

(begin[\s\S]*?\([\s\S]*?)foo([\s\S]*?\)[\s\S]*)

$1abc$2

Online regex demo

Online C++ demo

However, how do I replace all three foo in one pass? I tried lookarounds, but failed because of the quantifiers.

The end result should look like this:

begin foo even spaces and maybe new line(
some text only replace abc abc bar abc, keep the rest
)
some more text not replace foo here

Question update:

I am looking for a pure regex solution. That is, the question should be solved by only changing the search and replace strings in the online C++ demo.

Maybe it would be easier to get the text between brackets and do a replace all? Then you reconstruct the string. — npinti
– npinti, Commented Jan 27, 2016 at 8:52

Community · Accepted Answer · 2017-05-23 12:15:15Z

0

I have come up with this code (based on Benjamin Lindley's answer):

#include <iostream>
#include <regex>
#include <string>
int main()
{
    std::string input_text = "my text\nbegin foo even 14 spaces and maybe \nnew line(\nsome text only replace foo foo bar foo, keep the rest\n)\nsome more text not replace foo here";
    std::regex re(R"((begin[^(]*)(\([^)]*\)))");
    std::regex rxReplace(R"(\bfoo\b)");
    std::string output_text;
    auto callback = [&](std::string const& m){
        std::smatch smtch;
        if (regex_search(m, smtch, re)) {
            output_text += smtch[1].str();
            output_text += std::regex_replace(smtch[2].str().c_str(), rxReplace, "abc");
        } else {
            output_text += m;
        }
    };

    std::sregex_token_iterator
        begin(input_text.begin(), input_text.end(), re, {-1,0}),
        end;
    std::for_each(begin,end,callback);

    std::cout << output_text;
    return 0;
}

See IDEONE demo

I am using one regex to find all matches of begin...(....) and pass them into the callback function where only Group 2 is processed further (a \bfoo\b regex is used to replace foos with abcs).

I suggest using (begin[^(]*)(\([^)]*\)) regex:

(begin[^(]*) - Group 1 matching a character sequence begin followed with zero or more characters other than (
(\([^)]*\)) - Group 2 matching a literal ( followed with zero or more characters other than ) (with [^)]*) and a literal ).

edited May 23, 2017 at 12:15

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answered Jan 27, 2016 at 9:34

Wiktor Stribiżew

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2 Comments

Mathias Over a year ago

Hi, thanks. I am looking for a pure regexp solution. I already worked around this in code, but I would prefer to have all logic in one regex. I'll update my question to make it clearer. But nice solution anyway!

Wiktor Stribiżew Over a year ago

It is not possible to do with std::regex. It does not support \G operator, nor does it support an infinite width lookbehind.

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