1

I want to input a phrase and extract each character of the phrase:

int main()
{
    int i = 0;
    string line, command;
    getline(cin, line); //gets the phrase ex: hi my name is andy
    stringstream lineStream(line);
    lineStream>>command;
    while (command[i]!=" ") //while the character isn't a whitespace
    {
        cout << command[i]; //print out each character
        i++;
    }
}

however i get the error: cant compare between pointer and integer at the while statement

Andy
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2 Answers2

3

As your title "Extracting arguments using stringstream" suggests:

I think you're looking for this :

getline(cin, line); 
stringstream lineStream(line);

std::vector<std::string> commands; //Can use a vector to store the words

while (lineStream>>command) 
{
    std::cout <<command<<std::endl; 
   //commands.push_back(command); // Push the words in vector for later use
}
P0W
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0

command is a string, so command[i] is a character. You can't compare characters to string literals, but you can compare them to character literals, like

command[i]!=' '

However, you're not going to get a space in your string, as the input operator >> reads space delimited "words". So you have undefined behavior as the loop will continue out of bounds of the string.

You might want two loops, one outer reading from the string stream, and one inner to get the characters from the current word. Either that, or loop over the string in line instead (which I don't recommend as there are more whitespace characters than just space). Or of course, since the "input" from the string stream already is whitespace separated, just print the string, no need to loop over the characters.

To extract all words from the string stream and into an vector of strings, you can use the following:

std::istringstream is(line);
std::vector<std::string> command_and_args;

std::copy(std::istream_iterator<std::string>(is),
          std::istream_iterator<std::string>(),
          std::back_inserter(command_and_args));

After the above code, the vector command_and_args contains all whitespace delimited words from the string stream, with command_and_args[0] being the command.

References: std::istream_iterator, std::back_inserter, std::copy.

Some programmer dude
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  • lets say the user enters insertN andy xu, then the program first checks the command which is "insertN" then it calls another function that checks the arguments that corresponds to the command. How would i do this? – Andy Sep 22 '13 at 18:50
  • @Andy I would extract all words and put in a `std::vector`. Then index zero of the vector is always the command, and you can pass either that string or the whole vector to your validation function. – Some programmer dude Sep 22 '13 at 19:05
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    As per @keithb in http://stackoverflow.com/questions/53849/how-do-i-tokenize-a-string-in-c, this is also reasonably done using range based initialization, eliminating the need for `std::copy`. – John H. Aug 13 '15 at 03:03