Question

I have tested the encryption part of the program and it works just fine for individual files, or even things like “file1,file2,file3” but it doesn’t work with directories. The code looks fine to me, however when executing it gives me a segmentation fault.

It’s supposed to encrypt files in directory and write them in the same directory with a new extension (old name + “.wbf”) and decryption with extension removal upon the opposite. I’m only going to post the parts of code that deal with the files, the do_crypt function that works with individual files works just fine, and I think it’s not the source of my problems.

    // PHP explode function

    vector<string> explode (string text, char separator)

    {

        vector<string> split;

        int last_trip = 0, pos = 0;

        text += separator;

        for (pos = 0; pos < text.size(); pos++)

        {

            if (text[pos] != separator)

            {

                // continue with iteration

            }

            else

            {

                split.push_back(text.substr(last_trip, pos - last_trip));

                last_trip = pos + 1;

            }

        }

        return split;

    };

    // LINUX -- directory listing function
    string LS (string dir)
    {
        DIR *dp;
        vector<string> files;
        struct dirent *dirp;
        if ((dp = opendir(dir.c_str())) = NULL)
        {
            cout << "Error (" << errno << ") opening " << dir << endl;
            //return errno;
        }
        while ((dirp = readdir(dp)) != NULL)
        {
            files.push_back(string(dirp->d_name));
        }
        closedir(dp);
        string explosive = "";
        for (int i = 0; i < files.size(); i++)
        {
            explosive += files[i];
            if (i != (files.size() - 1)) { explosive += ','; } 
        }
        return 0;
    }

// various functions for encryption

int main (int argc, char* argv[])

{

    cout << "\t! ENCRYPTR -- File encryption utility written by WBlinder, 2010. !" << endl << endl;

    cout << "\t\t\t\tOPTIONS:" << endl;

    cout << "\t\t\t1\tCRYPT A FILE" << endl << "\t\t\t2\tDECRYPT A FILE" << endl << endl;

    cout << "choice > ";

    int opt;

    cin >> opt;

    string sin, sout;

    string dummy; getline(cin, dummy);

    /*cout << "input files > ";

    cout.clear(); cin.clear();

    getline(cin, sin);

    vector<string> fin = explode(sin, ',');

    cout << "output files > ";

    getline(cin, sout);

    vector <string> fout = explode(sout, ',');

    if (sin.size() != sout.size())

    {

        cout << "NO. INPUT FILES UNEQUAL NO. OUTPUT FILES" << endl;

        return 1;

    }*/
    string dir;
    cout << "dir > "; 
    getline (cin, dir);
    vector<string> input = explode(dir, ',');
    vector<string> output = input;
    switch (opt)
    {
        case 1:
            for (int i = 0; i < output.size(); i++)
            {
                output[i] = output[i] + ".wbf";
            }
            break;
        case 2:
            for (int i = 0; i < output.size(); i++)
            {
                output[i] = output[i].substr(0, (output[i].size() - 4));
            }
            break;
    }

    cout << "password > ";

    getline(cin, key);

    cout << "N > ";

    cin >> N;

    cout << "(768 => fairly secure\t3072 => secure)\nextra rounds > ";

    cin >> drop;

    for (int brick = 0; brick < input.size(); brick++)

    {

        do_crypt(opt, dir + input[brick], dir + output[brick]);

    }

    /*string text;

    cout << "text to split: ";

    getline (cin, text);

    vector<string> tnt = explode(text, '.');

    for (int i = 0; i < tnt.size(); i++)

    {

        cout << i << ": " << tnt[i] << endl;

    }*/

}

Answer 1

There is many problem in your LS function. First, you should make it directly return a vector<string> instead of packing the data in a string using a comma to separate value. This would save you a call to explode function, and would not break if the directory contains a filename with a comma in it (which is a valid name on Linux).

But the bigger problem (that is causing) your segfault is the return 0 line. Since your function is declared to return a string object, and since string class has an implicit constructor from const char*, this is interpreted by the compiler as return string(NULL). And when called with a NULL pointer this constructor raise a logic_error exception. As you didn’t catch the exception, the C++ runtime call the abort function. This function cause a segfault by design in order to stop execution (and if enabled generate a coredump to allow post-morten debugging).

You should at least rewritte your LS function like that:

string LS (string dir)
{
    DIR *dp;
    vector<string> files;
    struct dirent *dirp;
    if ((dp = opendir(dir.c_str())) == NULL)
    {
        cout << "Error (" << errno << ") opening " << dir << endl;
        return string();
    }
    while ((dirp = readdir(dp)) != NULL)
    {
        files.push_back(string(dirp->d_name));
    }
    closedir(dp);
    string explosive = "";
    for (int i = 0; i < files.size(); i++)
    {
        explosive += files[i];
        if (i != (files.size() - 1)) { explosive += ','; } 
    }
    return explosive;
}

Or better, change its signature to return a vector<string> and rewrite it like that:

vector<string> LS (string dir)
{
    DIR *dp;
    vector<string> files;
    struct dirent *dirp;
    if ((dp = opendir(dir.c_str())) != NULL)
    {
        while ((dirp = readdir(dp)) != NULL)
        {
            files.push_back(string(dirp->d_name));
        }
        closedir(dp);
    }
    else
    {
        cout << "Error (" << errno << ") opening " << dir << endl;
    }
    return files;
}