Question

This is my partial code:

if(action=="auth")
{


 myfile.open("account.txt");
    while(!myfile.eof())
    {
        getline(myfile,sline);

        vector<string> y = split(sline, ':');
    logincheck = "";
    logincheck = y[0] + ":" + y[3];

    if (sline==actionvalue)
    {
    sendClient = "login done#Successfully Login.";
    break;
    }
    else
    {
    sendClient = "fail login#Invalid username/password.";
    }

    y.clear();
    }
    myfile.close();

}

If i don’t have this

 logincheck = y[0] + ":" + y[3];

The code will not have any segmentation core dump error, but when I add that line, it will went totally wrong.

My account.txt is as followed:

admin:PeterSmite:hr:password
cktang:TangCK:normal:password

The split function:

std::vector<std::string> split(std::string const& str, std::string const& delimiters = "#") {
  std::vector<std::string> tokens;

  // Skip delimiters at beginning.
  string::size_type lastPos = str.find_first_not_of(delimiters, 0);
  // Find first "non-delimiter".
  string::size_type pos = str.find_first_of(delimiters, lastPos);

  while (string::npos != pos || string::npos != lastPos) {
    // Found a token, add it to the vector.
    tokens.push_back(str.substr(lastPos, pos - lastPos));
    // Skip delimiters.  Note the "not_of"
    lastPos = str.find_first_not_of(delimiters, pos);
    // Find next "non-delimiter"
    pos = str.find_first_of(delimiters, lastPos);
  }
  return tokens;
}



std::vector<std::string> split(std::string const& str, char const delimiter) {
  return split(str,std::string(1,delimiter));
}

Answer 1

You should do some basic input checking before you blithely assume that the vector contains at least 4 elements, otherwise y[3] will explode when you parse a line of input without three colons:

if (y.size >= 4) {
   // Do login check
} else {
   // Invalid input
}

I’d guess that you probably have a blank line in your input.

Wrap the whole section of code that relies on reading a “a:b:c:d” line of input:

if(action=="auth") {
  myfile.open("account.txt");
  while(getline(myfile,sline))
  {
    vector<string> y = split(sline, ':');
    if (y.size >= 4) {
      logincheck = "";
      logincheck = y[0] + ":" + y[3];

      if (sline==actionvalue) {
        sendClient = "login done#Successfully Login.";
        break;
      } else {
        sendClient = "fail login#Invalid username/password.";
      }
    }
  }
  myfile.close();
}