string tokenizer

[ruval002]

i have a problem with my following code, note: this is just part of my code
when i run it, lets say i enter hello world
it will output:
hello
segmentation fault

is there a way i can fix this?

void input::read_line()
{
  string command;
  while(command != "exit")
    {
      cout <<"Enter a command" << endl;
      cin >> command;
      string buf;
      stringstream ss(command);

      vector<string> tokens;
      while(ss >> buf)
        tokens.push_back(buf);

      cout << tokens[0] << endl;
      cout << tokens[1] << endl;
    }

[webJose]

You are assuming there will be at least two tokens in the 'tokens' vector. You must never make such assumptions, especially when coming from user input!

[Disch]

You're getting the segmentation fault because tokens[1] doesn't exist. The array is only 1 element big because you only put "hello" in it.

Remember the >> operator stops at whitespace, so when you say cin >> command you are only taking up to the first space... which is why you only get "hello". If you want to get the entire line, use getline:

getline( cin, command );

Also, you should never even allow the possibility of accessing outside of array bounds. If the user inputs fewer than 2 tokens, your program will fail. Check the size of tokens before you print, and make sure you never print past the end of the vector.

[ruval002]

how could i fix that for any number of tokens?

[Disch]

use a for loop. Loop from zero up to the size of the vector (ie: tokens.size()).

[ruval002]

ok so i changed it but im still getting a segmentation fault
i did the following input:
hello all of you
and i get the following output
hello
all
of
you
segmentation fault

 string command;
  while(command != "exit")
    {

      cout <<"Enter a command" << endl;
      getline(cin, command);
      string buf;
      stringstream ss(command);

      vector<string> tokens;
      while(ss >> buf)
        tokens.push_back(buf);

      for(int i = 0; tokens.size();i ++)
        cout << tokens[i] << endl;

[ruval002]

i actually dont need to print anything, it was just a test

i want to do something like this:

if(tokens[2] == "dirs")
{
//do something
}

i keep getting segmentation fault

[cire]

Probably because you don't compare tokens.size() to anything.

[timmyyyyy]

for(int i = 0; tokens.size();i ++) makes no sense

[ruval002]

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

[ruval002]

i dont need to print anything but how would i handle if the input is less than 2 tokens

string command;
  while(command != "exit")
    {
      cout <<"Enter a command" << endl;
      getline(cin, command);
      string buf;
      stringstream ss(command);
      vector<string> tokens;

      while(ss >> buf)
        tokens.push_back(buf);

      if(tokens[0] == "cd")
        {
// do something
        }
}
//.. 

[Disch]

if you aren't printing anything, then what is there to handle?

[ruval002]

if(tokens[0] == "cd")
        {
// i call a function here 
        }

so when the input is just one token "cd" it returns the home directory.
but if it has 2 inputs like cd hello it will go to that directory.
so the problem is that when i only input one token it gives me a segmentation fault

so basically what im trying to do is parse a command line and its arguments from user input