How can I use boost::regex on a boost::circular buffer?

Question

I'm capturing data in a boost::circular_buffer and would like to now perform a regex search on the contents but I'm having some difficulty getting boost::regex to understand how to look at the buffer.

Here's a stripped down version of the sort of thing I'd like to do based on the example here:

    // Set up a pre-populated data buffer as an example
    std::string test = "Fli<usefuldata>bble";
    boost::circular_buffer<char> dataBuff;
    for (std::string::iterator it = test.begin(); it != test.end(); ++it)
    {
        dataBuff.push_back(*it);
    }

    // Set up the regex
    static const boost::regex e("<\\w*>");
    std::string::const_iterator start, end;
    start = dataBuff.begin(); // <-- error C2679
    end = dataBuff.end();
    boost::match_flag_type flags = boost::match_default;

    // Try and find something of interest in the buffer
    boost::match_results<std::string::const_iterator> what;
    if (regex_search(start, end, what, e, flags))
    {
        // Do something - we found what we're after...
    }

I (quite understandably I think) get this error when I try to compile:

1>c:\projects\ProtocolBufferProcessor\ProtocolBufferProcessor.h(53): error C2679: binary '=' : no operator found which takes a right-hand operand of type 'boost::cb_details::iterator<Buff,Traits>' (or there is no acceptable conversion)
1>          with
1>          [
1>              Buff=boost::circular_buffer<char>,
1>              Traits=boost::cb_details::nonconst_traits<std::allocator<char>>
1>          ]
1>          c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\xstring(435): could be 'std::_String_iterator<_Elem,_Traits,_Alloc> &std::_String_iterator<_Elem,_Traits,_Alloc>::operator =(const std::_String_iterator<_Elem,_Traits,_Alloc> &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          while trying to match the argument list '(std::_String_iterator<_Elem,_Traits,_Alloc>, boost::cb_details::iterator<Buff,Traits>)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          and
1>          [
1>              Buff=boost::circular_buffer<char>,
1>              Traits=boost::cb_details::nonconst_traits<std::allocator<char>>
1>          ]

...but is there anything I can do other than create a std::string character by character from the circular buffer each time I run the regex?

I'm using Boost v1.54 if that makes a difference.

try to use auto for 'start' and 'end' variables and decltype(start) as a type parameter for 'what' variable. — Slava, Nov 07 '16 at 16:20
I tried changing to `auto start = dataBuff.begin();` but I get `error C4430: missing type specifier - int assumed. Note: C++ does not support default-int` — Jon Cage, Nov 07 '16 at 16:23
well, strictly speaking auto and decltype are not necessary, you can just put the proper iterator types (for cirucular buffer) manually. But that is a hassle. Which compiler do you use? — Slava, Nov 07 '16 at 16:30

score 1 · Accepted Answer · answered Nov 07 '16 at 16:34

you need to use the buffer's iterator type:

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#include <boost/circular_buffer.hpp>
#include <boost/regex.hpp>

using buffer_t = boost::circular_buffer<char>;

int main() {
    // Set up a pre-populated data buffer as an example
    std::string test = "Fli<usefuldata>bble";
    buffer_t dataBuff;
    for (std::string::iterator it = test.begin(); it != test.end(); ++it)
    {
        dataBuff.push_back(*it);
    }

    // Set up the regex
    static const boost::regex e("<\\w*>");

    buffer_t::const_iterator start = dataBuff.begin(); // <-- error C2679
    buffer_t::const_iterator end = dataBuff.end();
    boost::match_flag_type flags = boost::match_default;

    // Try and find something of interest in the buffer
    boost::match_results<buffer_t::const_iterator> what;
    if (regex_search(start, end, what, e, flags))
    {
        // Do something - we found what we're after...
    }
}

That does indeed solve the problem. Thanks very much :) – Jon Cage Nov 07 '16 at 17:09 — Jon Cage, Nov 07 '16 at 17:09

How can I use boost::regex on a boost::circular buffer?

1 Answers1