taking input of a string word by word

Question

I just started learning C++. I was just playing around with it and came across a problem which involved taking input of a string word by word, each word separated by a whitespace. What I mean is, suppose I have

   name  place animal

as the input. I want to read the first word, do some operations on it. Then read the second word, do some operations on that, and then read the next word, so on.

I tried storing the entire string at first with getline like this

    #include<iostream>
    using namespace std;
    int main()
    {
     string t;
     getline(cin,t);
     cout << t; //just to confirm the input is read correctly
    }

But then how do I perform operation on each word and move on to the next word?

Also, while googling around about C++ I saw at many places, instead of using "using namespace std" people prefer to write "std::" with everything. Why's that? I think they do the same thing. Then why take the trouble of writing it again and again?

[Why is “using namespace std” considered bad practice?](http://stackoverflow.com/q/1452721/995714) — phuclv, Apr 23 '17 at 15:47

score 60 · Accepted Answer · edited May 23 '17 at 12:03

60

Put the line in a stringstream and extract word by word back:

#include <iostream>
#include <sstream>
using namespace std;

int main()
{
    string t;
    getline(cin,t);

    istringstream iss(t);
    string word;
    while(iss >> word) {
        /* do stuff with word */
    }
}

Of course, you can just skip the getline part and read word by word from cin directly.

And here you can read why is using namespace std considered bad practice.

edited May 23 '17 at 12:03

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answered Aug 19 '13 at 16:51

jrok

54,456
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I tried reading with cin. But since the words are separated by a whitespace, cin seemed to read only the first word. A simple cin t; cout t; shows that. Hence I switched to getline. – aandis Aug 19 '13 at 16:55
@jrok getting compilation error on the code you gave. error: variable ‘std::istringstream iss’ has initializer but incomplete type – aandis Aug 19 '13 at 17:13
@zack Did you include ``? – jrok Aug 19 '13 at 17:20
@jrok what's the "iss" for ? – aandis Aug 19 '13 at 17:27
what exactly is `istringstream` ? A modified string type? – Abhinav Gauniyal Jun 01 '15 at 03:47
check **this page** :) : http://www.cplusplus.com/reference/sstream/istringstream/ – Jul 06 '15 at 09:55
Just wanted to ask the meaning of : while(iss >> word) : what exactly it is doing ? – Chandra Shekhar Dec 02 '18 at 11:01

score 6 · Answer 2 · answered Jul 31 '14 at 17:39

(This is for the benefit of others who may refer)

You can simply use cin and a char array. The cin input is delimited by the first whitespace it encounters.

#include<iostream>
using namespace std;

main()
{
    char word[50];
    cin>>word;
    while(word){
        //Do stuff with word[]
        cin>>word;
    }
}

score 1 · Answer 3 · edited May 23 '17 at 12:18

1

getline is storing the entire line at once, which is not what you want. A simple fix is to have three variables and use cin to get them all. C++ will parse automatically at the spaces.

#include <iostream>
using namespace std;

int main() {
    string a, b, c;
    cin >> a >> b >> c;
    //now you have your three words
    return 0;
}

I don't know what particular "operation" you're talking about, so I can't help you there, but if it's changing characters, read up on string and indices. The C++ documentation is great. As for using namespace std; versus std:: and other libraries, there's already been a lot said. Try these questions on StackOverflow to start.

edited May 23 '17 at 12:18

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answered Aug 19 '13 at 16:58

Maddy Byahoo

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Number of words in the string are unknown. Any method to read the words with cin then? – aandis Aug 19 '13 at 17:03
http://stackoverflow.com/questions/8683302/how-to-split-a-space-separated-string-into-multiple-strings-in-c – Maddy Byahoo Aug 19 '13 at 17:06
you can do something with getline and deliminating characters too http://www.minich.com/education/wyo/cplusplus/cplusplusch10/getfunction.htm – Maddy Byahoo Aug 19 '13 at 17:15

taking input of a string word by word

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