CODEWITHSUNDEEP
c++stringstream
user1258934
user1258934

Reputation: 13

C++ Stringstream: Accepts a string, but not a string stored in a variable. Why?

I've been trying to split up an input string into smaller strings delineated by whitespace. I found this code from here: 

stringstream ss ("bla bla");
string s;

while (getline(ss, s, ' ')) {
cout << s << endl;
}

which works just fine. However, if I replace "bla bla" with a variable containing a string:

string userInput;
cin >> userInput;

stringstream ss (userInput);
string s;

while (getline(ss, s, ' ')) {
cout << s << endl;
}

only the first word/char/string prints out. Why is that? Is there a way to fix it? I've looked around at some stringstream questions, but the problem is that I don't really know what I'm looking for.

Upvotes: 1

Views: 3347

Answers (2)

Zeta
Zeta

Reputation: 105955

Your problem isn't stringstream ss (userInput);, it's the behavior of std::cin. Any whitespace will end the extraction of formatted user input, so the input bla bla will result in one std::string s = "bla" and another string "bla" waiting for extraction.

Use cin >> noskipws >> userInput; instead. If you want to get a line, use std::getline(std::cin,userInput) instead. Have a look at this little demonstration, which compares std::getline to std::cin::operator>> on your input bla bla:

Source:

#include <iostream>
#include <string>

int main(){
        std::string userInput;

        std::cout << "Using std::getline(std::cin,userInput) on input \"bla bla\"." << std::endl;
        std::getline(std::cin,userInput);
        std::cout << "userInput contains \"" << userInput << "\"" << std::endl;

        std::cout << "std::cin >> userInput on input \"bla bla\"." << std::endl;
        std::cin >> userInput;
        std::cout << "userInput contains \"" << userInput << "\"" << std::endl;
        return 0;
}

Result:

Using std::getline(std::cin,userInput) on input "bla bla".
userInput contains "bla bla"
std::cin >> userInput on input "bla bla".
userInput contains "bla"

See also:

Upvotes: 8

Tobias Langner
Tobias Langner

Reputation: 10828

This does what you said:

#include "stdafx.h"
#include <string>
#include <sstream>
#include <iostream>

int _tmain(int argc, _TCHAR* argv[])
{
    std::string test("bla bla");
    std::stringstream stream(test);
    std::string temp;
    while (getline(stream, temp, ' ')) {
       std::cout << temp << std::endl;
    }
    return 0;
}

It is even what you said you did. But since it works - where is the difference to your code?

And for those who do not have a Microsoft Visual C++ compiler handy and do not understand the differences, here's a code snippet:

std::string test("bla bla");
std::stringstream stream(test);
std::string temp;
while (getline(stream, temp, ' ')) {
   std::cout << temp << std::endl;
}

the includes required by that snippet are: <string>, <sstream> & <iostream>. Please insert it into the required method.

Upvotes: 0

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