How count and store files from a directory in a vector

Question

I'm trying to call all existing ".stl" files in a given directory, and use them to build my geometry in Geant4. This is a separate program I've made to test it before I add it to my Geant4 code.

As for now, I've been trying to get the number of files via system command. The problem is that it always returns the correct number of files, 32, and then it returns Zero (0). Therefore, I cannot use it in a for loop. Furthermore, when I print the files, I have the "." and "..", which is not what I want.

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
#include <cstring>

#include <sys/types.h>
#include <dirent.h>

typedef std::vector<std::string> stringvec;

void read_directory(const std::string& name,stringvec& v)
{
    DIR* dirp = opendir(name.c_str());
    struct dirent * dp;
    while ((dp = readdir(dirp)) != NULL) {
        v.push_back(dp->d_name);
    }
    closedir(dirp);
}

int main()
{
    int NbOfComponents;
    stringvec v;
    std::string Ext = ".stl";
    std::string Dir = "/home/lghizoni/Geant4/SpaceRadiationFramework/Geometry/Satlab/";
    std::string command = "ls -l "+Dir+"*"+Ext+"|wc -l";
    const char *Command = command.c_str();
    NbOfComponents = system(Command);
    read_directory(Dir,v);
    std::cout<<"The geometry is composed by "<<NbOfComponents<<" parts"<<std::endl;
    std::copy(v.begin(),v.end(),std::ostream_iterator<std::string>(std::cout,"\n"));

First of all, I wanted to store the number of files in NbOfComponents, so I could use it in a loop later to call each of the parts. The problem is that it returns Zero as can be seen here in the output:

32
The geometry is composed by 0 parts
Assembly 5 - M2x10_TX6.stl
Assembly 5 - castor-v020 (3).stl
Assembly 5 - Sshield_bottom.stl
Assembly 5 - castor-v020 (7).stl
Assembly 5 - M2x10_TX6_1.stl
Assembly 5 - M2x10_TX6_12.stl
.
Assembly 5 - castor-v020 (2).stl
..
Assembly 5 - M2x10_TX6_14.stl
Assembly 5 - M2x10_TX6_9.stl
Assembly 5 - M2x10_TX6_7.stl
Assembly 5 - Sshield_top.stl
Assembly 5 - castor-v020 (1).stl
Assembly 5 - castor-v020 (11).stl
Assembly 5 - M2x10_TX6_13.stl
Assembly 5 - M2x10_TX6_10.stl
Assembly 5 - M2x10_TX6_3.stl
Assembly 5 - M2x10_TX6_8.stl
Assembly 5 - M2x10_TX6_5.stl
Assembly 5 - castor-v020 (12).stl
Assembly 5 - M2x10_TX6_2.stl
Assembly 5 - M2x10_TX6_11.stl
Assembly 5 - castor-v020 (5).stl
Assembly 5 - castor-v020 (13).stl
Assembly 5 - castor-v020 (6).stl
Assembly 5 - castor-v020 (14).stl
Assembly 5 - M2x10_TX6_4.stl
Assembly 5 - castor-v020 (8).stl
Assembly 5 - castor-v020 (9).stl
Assembly 5 - M2x10_TX6_6.stl
Assembly 5 - castor-v020 (4).stl
Assembly 5 - castor-v020.stl
Assembly 5 - castor-v020 (10).stl

The last point is that it returns "." and "..", which as I understand, are directories. With that I cannot call each of them from the vector v[i]. Any inputs will be most appreciated, and thanks in advance :)

Answer 1

system command doesn't return the out of the command applid it returns error code success / failure

check this from man page

SYNOPSIS
       #include <stdlib.h>
       int system(const char *command);
DESCRIPTION
       The system() library function uses fork(2) to create a child process that executes the shell command specified in command using execl(3) as follows:
           execl("/bin/sh", "sh", "-c", command, (char *) 0);
       system() returns after the command has been completed.
       During execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored, in the process that calls system() (these signals will be handled according to their defaults
       inside the child process that executes command).
       If command is NULL, then system() returns a status indicating whether a shell is available on the system

You can use popen command to get output of system command applied

  FILE *fp;
  char data[100];
  std::string command = "ls -l "+Dir+"*"+Ext+"|wc -l";
  const char *Command = command.c_str();
  fp = popen(Command, "r");
  while (fgets(data, sizeof(data), fp) != NULL) 
    {
      printf("%s", data);
    }
  pclose(fp);

And about "." & ".." you should directly compare and ignore those two files as those will always be there presenting current and parent of current directory

Answer 2

So the first problem is that system does not return the output of the command, it returns the exit code of the command, An exit code of 0 means that the command executed successfully.

Second problem is simple to solve, just change your read_directory function like this

    v.push_back(dp->d_name);

to

    if (strcmp(dp->d_name, ".") != 0 && strcmp(dp->d_name, "..") != 0)
        v.push_back(dp->d_name);

This means that the special directories . and .. don't get added to your vector.

Now to get the number of components you could do this

NbOfComponents = v.size();

But that would not work if there are any files in your directory that are not named *.stl. In that case further modify read_directory so that you do not push_back any file name that does not end with .stl