This don't compile, why?

#include <iostream>
#include <string>
int main()

{
std::string stringvalues;
stringvalues = "31.5";

// error message with this line, say: varialbe 'std::istringstream iss' has but incomplete type
std::istringstream iss(stringvalues);
double f;
iss>>f;
std::cout <<"Value is:"<< f <<std::endl;
return (0);
}

g++ verison is 3.3.2

Add a line like this, now it is OK.

#include <sstream>

And I don't think that you should use istringstreams, as it is better to stick with strings or c style character arrays. This is because the implementation of istringstreams are vendor dependent, and your resultant program may not be portable if you use them.

Could you provide a link or some examples to qualify this, please?

istringstream and ostringstream are part of the c++ standard library and definatly should be used, i think there is a problem with strstream which might be what your thinking of but certanly istringstream and ostringstream are great and definatly should be used.

Yes, I am sorry. I confused strstreams with istringstreams. SORRY!

No worries :-)

Just trying to keep explanations clear for future reference (LQ seems to turn up on google for at least 50% of my Linux queries now).

strstream is indeed deprecated now - various problems I know of included:

no null terminated string returned from str() unless inserted,
the ability to use programmer allocated buffer (inconsistent),
and the need to block access to the underlying buffer to get the string and unblock to insert / extract again.

I guess it was just too confusing - I am pretty sure there is a section on this in Josuttis (my copy is at home right now, I am not).