vector<string>を全結合

accum_string.cpp

#include <iostream>
#include <vector>
#include <numeric>
#include <string>

using namespace std;

int main(){

    vector<string> A = {"I", "have", "a", "pen."};

    string sum_A = accumulate(A.begin() + 1, A.end(), A[0], [](string &init, string &v){ return init + v; });
    cout << sum_A << "\n"; // "Ihaveapen."

    string sum_A2 = accumulate(A.begin() + 1, A.end(), A[0], [](string &init, string &v){ return init + " " + v; });
    cout << sum_A2 << "\n"; // "I have a pen."

    auto f =  [](string &init, string &v) -> string { return init + " " + v; };
    string sum_A3 = accumulate(A.begin() + 1, A.end(), A[0], f);
    cout << sum_A3 << "\n"; // "I have a pen."

    const string delim = ", ";
    auto f2 =  [&delim](string &init, string &v) -> string { return init + delim + v; };
    string sum_A4 = accumulate(A.begin() + 1, A.end(), A[0], f2);
    cout << sum_A4 << "\n"; // "I, have, a, pen."

    return 0;
}