storing structure data in circular buffer

Question

I need to store a string along with an integer in a circular buffer and then have to iterate through it, searching (with a substr) for existence of a string which then gets copied along with the integer into result buffer. I've written the below proof of concept code but it terminates pre-maturely after the first time &res gets copied into out and I'm not exactly sure why, can anyone help me here?
This is what I have so far:

#include <iostream>
#include <boost/circular_buffer.hpp>
#include <boost/algorithm/string/predicate.hpp>

#define CB_SZ   4
#define ARR     7

struct cb_dat_t{
    std::string lp;
    int cnf;
};

int buffer_check(cb_dat_t &in, boost::circular_buffer<cb_dat_t> &buff, cb_dat_t *out);
 int main(void)
 {
    int i = 0;
    cb_dat_t in[ARR];
    cb_dat_t out;
    boost::circular_buffer<cb_dat_t> cb(CB_SZ);

    in[0].lp = "ABC";
    in[0].cnf = 78;
    in[1].lp = "ABCDE";
    in[1].cnf = 63;
    in[2].lp = "AB";
    in[2].cnf = 92;
    in[3].lp = "1234";
    in[3].cnf = 85;
    in[4].lp = "23";
    in[4].cnf = 71;
    in[5].lp = "ABC";
    in[5].cnf = 63;
    in[6].lp = "BC";
    in[6].cnf = 71;

    for (i=0; i<ARR; i++) {
    buffer_check(in[i], cb, &out);
    std::cout << "result[" << i << "] " << out.lp << " " << out.cnf << std::endl;
    }
    std::cout << "all done!" <<std::endl;
return 0;
 }

int buffer_check(cb_dat_t &in, boost::circular_buffer<cb_dat_t> &buff, cb_dat_t *out)
{
    cb_dat_t res;

    if (!buff.size()){
        std::cout << "buff.size() " << buff.size() << std::endl;
        buff.push_back(in);
        memcpy(out,&in,sizeof(cb_dat_t));
        return 0;
    }

    boost::circular_buffer<cb_dat_t>::iterator itr = buff.begin();
    while (itr!=buff.end()) {
        if (boost::contains(itr->lp,in.lp)) {
            std::cout << itr->lp << " contains " << in.lp << std::endl;
            memcpy(&res,&itr,sizeof(cb_dat_t));
        } else {
            std::cout << itr->lp << " does not contain " << in.lp <<std::endl;
            memcpy(&res,&in,sizeof(cb_dat_t));
        }
        itr++;
    }
    buff.push_back(in);
    memcpy(out,&res,sizeof(cb_dat_t));
    std::cout << "buff.size() " << buff.size() << std::endl;
    return 0;
}

Where the output is:

./circular
buff.size() 0
result[0] ABC 78
ABC does not contain ABCDE
buff.size() 2

Command terminated

I'm not sure why g++ needs me to do memcpy(&res,&itr,sizeof(cb_dat_t)); , itr is a pointer already, isn't it? It complains when I do memcpy(&res,itr,sizeof(cb_dat_t)); instead.

Answer 1

You shouldn't be using memcpy at all. Since cb_dat_t is not a POD type (in this case because it contains a member with a constructor), you should be using the assignment operation to copy cb_dat_t objects. The four memcpy calls in buffer_check can be replaced with

*out = in;
res = *itr;
res = in;
*out = res;

memcpy will not handle std::string properly. The compiler generated default assignment operator for cb_dat_t will properly copy all members of the structure.