检查 C++ 中的空目录时出错

Question

I'm trying to create a folder named by todays date (on Ubuntu) and then check if it's empty or not.

The empty-or-not check will be done several times daily.

#include <cstdlib>
#include <unistd.h>
#include <stdio.h>
#include <iostream>
#include <typeinfo>
#include <chrono>
#include <time.h>
#include <iomanip>

using namespace std; 

int main() {
  //Pull out system date and create a folder named by system date
  auto const now = std::chrono::system_clock::now();
  auto const in_time_t = std::chrono::system_clock::to_time_t(now);
  std::stringstream ss;
  ss << std::put_time(std::localtime(&in_time_t), "%d_%m_%Y"); 
    
  // Creating todays date folder with entry folder
  string str_2=std::string("mkdir -p " + string(ss.str()) + "/entry");
  const char *com2=str_2.c_str();
  system(com2);
   
  //check if directory is empty or not
  int check;
  char is_empty[100];
  FILE * output;
  output = popen("ls " + ss.str() + "/entry | wc -l","r") ; 
  fgets (is_empty, 100, output); //write to the char
  pclose (output);
  check = atoi(is_empty);
  if (check == 0) {
    cout << "The folder is empty" << endl;
  } 
}

I'm getting this error when compiling this code:

error: no match for ‘operator+’ (operand types are ‘const char [4]’ 
    and ‘std::stringstream {aka std::__cxx11::basic_stringstream<char>}’)
         output = popen("ls " +ss+ "/entry | wc -l","r") ;

Answer 1

This solved it for me

int check;
char is_empty[100];
FILE * output;

string cmd = std::string("ls " + string(ss.str())+ "/entry | wc -l") ;
const char *com4 = cmd.c_str(); 
output = popen(com4,"r");
fgets(is_empty, 100, output);
pclose (output);
check = atoi(is_empty);
//cout << check<<endl;
if (check == 0){
    cout << "The folder is empty" << endl;
   }