[Boost-users] [regex] using partial_match?

Subject: [Boost-users] [regex] using partial_match?
From: Armel Asselin (armelasselin_at_[hidden])
Date: 2013-03-19 09:02:15

[boost 1.53.0]

Hello,

I'd like to find in a stream of text either "abcd" or "ab". The text is not 
bounded in size, so I think I should use partial_match.

However I present it the following text: "hello abc<cut_here>d, how are 
you?"

it reports to find "ab" and does not wait for the second block to be 
appended.

#include "boost/regex.hpp"

int main(int argc, char* argv[])
{
    boost::regex re ("abcd|ab");
    std::string str ("hello abc");

    boost::match_results<std::string::const_iterator> results;

    bool found = boost::regex_search (str.cbegin(), str.cend(), results, re, 
boost::regex_constants::match_partial);

    if (!found || results[0].matched)
        printf("problem...\n");

    return 0;
}

Am I doing something wrong?
I see in the specification that "Specifies that if no match can be found, 
then ....", isn't this specification flowed?
should not it be "if the regular expression engine needs to check past the 
end of the block of text, and the start matches partially, ...." ?

I hope I am wrong and there are good flags to pass....

Regards
Armel