std::copy doesn't copy vector in C-CodePudding

To find all sequences of fixed length which contain only 0 and 1 I use this code:

#include <bits/stdc  .h>

typedef long long int lli;
typedef std::vector<lli> vec_lli;
typedef std::vector<std::string> vec_s;

void print_array(vec_s arr) {
  std::cout << '[';
  int n = arr.size();
  for (size_t i = 0; i < n; i  ) {
    std::cout << arr[i];
    if (i < (n - 1)) {
      std::cout << ", ";
    }
  }
  std::cout << ']' << std::endl;
}

vec_s get_variants(int n) {
  vec_s result = {"0", "1"};
  vec_s temp;
  temp.reserve(2);
  result.reserve(2);
  for (int i=0; i < (n - 1);   i) {
    std::copy(result.begin(), result.end(), temp.end()); // 1
    for (int j=0; j < result.size();   j) {
      temp[j]  = "0";
      result[j]  = "1";
    }
    std::copy(temp.begin(),temp.end(), result.end());
    temp.clear();
  }
  return result;
}

int main(int argc, char const *argv[]) {
  int n;
  std::cin >> n;
  vec_s mb = get_variants(n);
  print_array(mb);
  return 0;
}

But vector temp is empty, before copying in line 1 and after. So, my program's output was [0111, 1111]. What I'm doing wrong?

CodePudding user response：

You are writing to temp.end() and result.end(). These iterators represent "one past the end", and therefore writing to these iterators is Undefined Behavior.

You seem to be looking for std::back_inserter. This is an iterator that will insert a new element to your container when it is written through.

std::copy(result.begin(), result.end(), std::back_inserter(temp));

CodePudding user response：

reserve does't increse vector size.