Question

I haven’t coded this bit up yet, because I’m not sure of which is the best method to tackle this.

For starters, what the program does now is simply put the names of all the files in the same directory as the program into an array of strings and then print that array out.

What I want to do is sort these by file extension. There will be a list of particular extensions for the user to choose from, after which all files with that extension in the folder will be returned to the user.

I’m just not sure how to go about that. The first thing that comes to mind is to iterate through the vector and compare each string to another string with the desired extension, and if there is match then push that string into another vector that is specific for that file extension. There are only 5 extensions I’m looking for so it’s not like I would have to make a whole ton of new vectors for each extension.

Alternativley I thought it might also make sense to never populate the original vector, and take the users request first and then iterate through the files and push all files with matching extensions into a specific vector. Once done if they choose another option the vector will simply be cleared and re-populated with the new file names.

Any tips on how to go about actually doing the comparison, I’m not that good with c++ syntax, also would it be wise to use a different type of container?

Thanks a lot for any and all advice you guys are willing to throw my way, it’s greatly appreciated!

#include <iostream>
#include <filesystem>
#include <vector>
using namespace std;
using namespace std::tr2::sys;


void scan( path f, unsigned i = 0 )
{
string indent(i,'\t');
cout << indent << "Folder = " << system_complete(f) << endl;
directory_iterator d( f );
directory_iterator e;

vector<string>::iterator it1;

std::vector<string> fileNames;


for( ; d != e; ++d )
{
    fileNames.push_back(d->path());

    //print out conents without use of an array
    /*cout << indent << 
        d->path() << (is_directory( d->status() ) ? " [dir]":"") <<
        endl;*/

    //if I want to go into subdirectories
    /*if( is_directory( d->status() ) )
        scan( f / d->path(), i + 1 );*/
}

for(it1 = fileNames.begin(); it1 != fileNames.end(); it1++)
{
 cout << *it1 << endl;
}



}


int main()
{
    path folder = "..";

    cout << folder << (is_directory( folder ) ? " [dir]":"") << endl;

    scan( folder );
}

Answer 1

You don’t mean ‘sort’, you mean ‘filter’. Sort means something else entirely.

Your second option seems the best, why do the extra work with two vectors?

As for the comparison, the difficulty is that the thing you are looking for is at the end of the string, and most searching functions operate from the start of the string. But there is a handy thing in C++ called a reverse iterator which scans a string backwards from the end, not forwards from the start. You call rbegin() and rend() to get a string’s reverse iterators. Here’s a comparison function using reverse iterators.

#include <algorithm>
#include <string>

// return true if file ends with ext, false otherwise
bool ends_with(const std::string& file, const std::string& ext)
{
    return file.size() >= ext.size() && // file must be at least as long as ext
        // check strings are equal starting at the end
        std::equal(ext.rbegin(), ext.rend(), file.rbegin());
}