Question

Possible Duplicate:
How to clear stringstream?

I have this c++ command

//siteurl and filename are of string type


stringstream ss;
ss << "lynx -dump '" << siteurl << "' > " << filename;

On first loop, everything ok. But on second loop i realize it just append instead of create a new record

as i troubleshoot using cout it give me this, I realize the command is append instead of overwrite on 2nd loop, how do I null or reset or overwrite first record of ss (stringstream) on 2nd loop/usage.

Webparser: lynx -dump 'http://sg.finance.yahoo.com/q?s=USDSGD=X' > file.txtlynx -dump 'http://sg.finance.yahoo.com/q?s=EURUSD=X' > file.txt

What i want is on 2nd loop it will be this output

Webparser: lynx -dump 'http://sg.finance.yahoo.com/q?s=EURUSD=X' > file.txt

I am new to C++, thanks for all help, greatly apperciated.

Answer 1

Do ss.str("") to make it empty.

But it is better to define ss inside the loop, so that each time it’s a new variable:

for(/*.....*/)
{
   stringstream ss;
   ss << /*....*/ ;
}

That is, make it a scope variable, e.g function-scope or block-scope, so that when it goes out of scope it is destructed, and when it comes back, it gets created again.

Making it a scope variable is less error prone than using ss.str("") to make it empty. I mean, what if you forgot to do ss.str("")? In many cases, when you need to write ss.str("") indicates that you actually need to make it a scope variable, so that you could define it again, either in a loop (as shown above), or entirely a new variable, probably with a different name.