reading a sequence of files within a folder

edit

edit: It seems that there is an embedded function (many thanks to @berak for pointing that out) that does this job, have a look on the example below:

int main()
{
    vector<String> filenames; // notice here that we are using the Opencv's embedded "String" class
    String folder = "<some_folder_path>"; // again we are using the Opencv's embedded "String" class

    glob(folder, filenames); // new function that does the job ;-)

    for(size_t i = 0; i < filenames.size(); ++i)
    {
        Mat src = imread(filenames[i]);

        if(!src.data)
            cerr << "Problem loading image!!!" << endl;

        /* do whatever you want with your images here */
    }
}

this is what I am using so far with success:

// you need these includes for the function
//#include <windows.h> // for windows systems
#include <dirent.h> // for linux systems
#include <sys/stat.h> // for linux systems

/* Returns a list of files in a directory (except the ones that begin with a dot) */

void readFilenames(std::vector<string> &filenames, const string &directory)
{
#ifdef WINDOWS
    HANDLE dir;
    WIN32_FIND_DATA file_data;

    if ((dir = FindFirstFile((directory + "/*").c_str(), &file_data)) == INVALID_HANDLE_VALUE)
        return; /* No files found */

    do {
        const string file_name = file_data.cFileName;
        const string full_file_name = directory + "/" + file_name;
        const bool is_directory = (file_data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0;

        if (file_name[0] == '.')
            continue;

        if (is_directory)
            continue;

        filenames.push_back(full_file_name);
    } while (FindNextFile(dir, &file_data));

    FindClose(dir);
#else
    DIR *dir;
    class dirent *ent;
    class stat st;

    dir = opendir(directory.c_str());
    while ((ent = readdir(dir)) != NULL) {
        const string file_name = ent->d_name;
        const string full_file_name = directory + "/" + file_name;

        if (file_name[0] == '.')
            continue;

        if (stat(full_file_name.c_str(), &st) == -1)
            continue;

        const bool is_directory = (st.st_mode & S_IFDIR) != 0;

        if (is_directory)
            continue;

//        filenames.push_back(full_file_name); // returns full path
        filenames.push_back(file_name); // returns just filename
    }
    closedir(dir);
#endif
} // GetFilesInDirectory

int main()
{
    string folder = "/documents/images/";
    vector<string> filenames;

    readFilenames(filenames, folder);

    for(size_t i = 0; i < filenames.size(); ++i)
    {
        Mat src = imread(folder + filenames[i]);

        if(!src.data)
            cerr << "Problem loading image!!!" << endl;

        /* do whatever you want with your images here */
    }
}

an alternative is to use the boost library check below:

// files you need to include, do not forget to include the -lboost_filesystem and -lboost_system libraries otherwise you will get quite some errors/complaints during the compilation
#include <boost/filesystem.hpp>
using namespace boost::filesystem;

void readFilenamesBoost(vector<string> &filenames, const string &folder)
{
    path directory(folder);
    directory_iterator itr(directory), end_itr;

    string current_file = itr->path().string();

    for(;itr != end_itr; ++itr)
    {
// If it's not a directory, list it. If you want to list directories too, just remove this check.
       if (is_regular_file(itr->path()))
       {
       // assign current file name to current_file and echo it out to the console.
//            string full_file_name = itr->path().string(); // returns full path
            string filename = itr->path().filename().string(); // returns just filename
            filenames.push_back(filename);
       }
    }
}

int main()
{
    string folder = "/documents/images/";
    vector<string> filenames;

    readFilenamesBoost(filenames, folder);

    for(size_t i = 0; i < filenames.size(); ++i)
    {
        Mat src = imread(folder + filenames[i]);

        if(!src.data)
            cerr << "Problem loading image!!!" << endl;

        /* do whatever you want with your images here */
    }
}