?
Solved

sstream basics

Posted on 2004-04-01
13
Medium Priority
?
829 Views
Last Modified: 2009-07-29
I want to convert a string of digits (may include +,-,.) to a double using sstream. plz give a good general example. so far I have found that I can convert the string to a buffer (I don't know how I can do that) and read from that buffer into a double.

thx Xperts
J
0
Comment
Question by:jhshukla
  • 7
  • 4
  • 2
13 Comments
 
LVL 10

Assisted Solution

by:Sys_Prog
Sys_Prog earned 75 total points
ID: 10738766
Have a look at this code

#include <iostream>
#include <string>
#include <sstream>

using namespace std ;

int main(int argc, char* argv[])
{
      string test ( "123.543  162.124 542 123.134" ) ;
      stringstream str ( test ) ;
      double d1, d2, d3 ;
      int i, j ;
      
      str >> d1 ;
      cout << "D1 : " << d1 << endl ;
      str >> d2 ;
      cout << "D2 : " << d2 << endl ;
      str >> i ;
      cout << "i : " << i << endl ;      

      str >> j ;
      cout << "j : " << j << endl ;      
      str >> d3 ;
      cout << "D3 : " << d3 << endl ;
       
       
      system("pause");
      return 0;
}


Amit
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10738781
This should give you a kick start...
--------8<--------
#include <iostream>
#include <sstream>

int main()
{
        std::string str = "-39.76 8.76e-99";
        std::istringstream istr(str);
        double d;
        while (istr >> d)
                std::cout << "Here's a double " << d << '\n';
}
--------8<--------
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10738784
[Sorry Amit got there first!]
0
Never miss a deadline with monday.com

The revolutionary project management tool is here!   Plan visually with a single glance and make sure your projects get done.

 
LVL 10

Expert Comment

by:Sys_Prog
ID: 10738792
No probs  rstaveley, happens quite a lot at EE

Amit
0
 
LVL 9

Author Comment

by:jhshukla
ID: 10741026
perfect! now you guys can clear a few doubts --
is it possible to add some more text to the stringstream after starting to extract from it? if yes where will the text be placed - at index 0 or at the end?

is there a way to extract the whole buffer NOT using [[[> s_stream >> some_string_variable <]]]?

plz also look at two peices of code below and corresponding output on VC++6.0

thx
J

EXAMPLE 1
=======
#include <sstream>
#include <iostream>
#include <string>

using namespace std;

int main(){
      string s = "345.89 23.9 3e-6 4";
      stringstream str(s);
      double d; int i;
      for(i=0; i<4; i++){
            str >> d;
            cout << d << endl;
      }
      return 0;
}
OUTPUT 1
------------
345.89
23.9
3e-006
4

EXAMPLE 2
=======
#include <sstream>
#include <iostream>
#include <string>

using namespace std;

int main(){
      string s = "345.89 23.9 3e-6 4";
      stringstream str(s);
      str << " 56.7";
      double d; int i;
      for(i=0; i<5; i++){
            str >> d;
            cout << d << endl;
      }
      return 0;
}
OUTPUT 2
------------
56.79
23.9
3e-006
4
4
:::::::::::::::::
 end of output
:::::::::::::::::
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10741938
You can get it to work bidirectionally, provided you don't use the std::string constructor.

i.e. This works:
--------8<--------
#include <iostream>
#include <sstream>
#include <string>

int main()
{
      std::stringstream sstr;
      sstr << "the rapist Mr physio";
            // Don't use constructor for this
            // otherwise you get an istringstream

      std::string str;
      for (int i = 0;i < 2;i++) {
            sstr >> str;
            sstr << str;
      }

      while (sstr >> str)
            std::cout << ' ' << str;
      std::cout << '\n';
}
--------8<--------

This doesn't work, because it constructs an istringstream:

      std::stringstream sstr("the rapist Mr physio");
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10741949
NB: If there's any danger of emptying the stringstream after an extraction, you should call sstr.clear() to clear the flags before inserting.
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10741981
You fix the error in EXAMPLE 2, by doing the following:

--------8<--------
    for(i=0; i<5; i++){
          if (str >> d)
              cout << d << endl;
     }
--------8<--------

There are only four tokens, but you attempt to extract 5. The fifth token fails, because you are EOF, but you are not testing the result of the extraction. You therefore see the 4th token twice.
0
 
LVL 9

Author Comment

by:jhshukla
ID: 10755058
thanks, i got that. but one part of the question is still unanswered.
 )= is there a way to extract the entire buffer NOT using [[[> s_stream >> some_string_variable <]]]?

0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10755782
Yes, use sstr.str(). It rturns the contents of the buffer in a std::string.

See http://www.cplusplus.com/ref/iostream/stringstream/str.html
0
 
LVL 9

Author Comment

by:jhshukla
ID: 10808781
how do I get errorflags or exception when I extract a number from sstream and it fails. eg

stringstream str("b456");
double d;
str >>d; // error! how do I catch it?
0
 
LVL 17

Accepted Solution

by:
rstaveley earned 150 total points
ID: 10830938
Sorry about the late response, I've just got back from holiday.

if (!(str >>d))
   throw YourException();
0
 
LVL 9

Author Comment

by:jhshukla
ID: 10855340
Amit, plz don't be pissed off. I gave more points to rstaveley 'coz of his/her continued response.
thx both of u.
0

Featured Post

Take Control of Web Hosting For Your Clients

As a web developer or IT admin, successfully managing multiple client accounts can be challenging. In this webinar we will look at the tools provided by Media Temple and Plesk to make managing your clients’ hosting easier.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Templates For Beginners Or How To Encourage The Compiler To Work For You Introduction This tutorial is targeted at the reader who is, perhaps, familiar with the basics of C++ but would prefer a little slower introduction to the more ad…
Article by: evilrix
Looking for a way to avoid searching through large data sets for data that doesn't exist? A Bloom Filter might be what you need. This data structure is a probabilistic filter that allows you to avoid unnecessary searches when you know the data defin…
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.

599 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question