How to clear the buffer of a streamstring?

Question

I have a streamstring in two loops and it is burning my RAM. So how to clear properly the buffer of a steamstring? It is like that to simplify :

stringstream ss (stringstream::in | stringstream::out); for() { for() { val = 2; ss << 2; mystring = ss.str(); // my stuff } // Clear the buffer here }

It wrote 2 then 22 then 222... I tried .clear() or .flush() but it is not that. So how I do this?

If I put std::stringstream ss; in a loop it will creat many ss in the RAM and will burn it no? Or it will delete ss at the end of his loop because it is created in a loop? (It feel a noob question here :) but I am! ) — bdelmas
– bdelmas, Commented Jun 16, 2011 at 10:52
it is created and destroyed as the program loops. BTW, what do you mean with "burn the RAM"? — Marius Bancila
– Marius Bancila, Commented Jun 16, 2011 at 13:49
My app grow in 30s at 2Go and crash. "it is created and destroyed as the program loops" I didn't know that, I thought it create many ss and they would destroy at the end of the function/app/object. Thank you — bdelmas
– bdelmas, Commented Jun 16, 2011 at 14:03

James Kanze · Accepted Answer · 2011-06-16 10:23:58Z

8

The obvious solution is to use a new stringstream each time, e.g.:

for (...) { std::stringstream ss; for (...) { // ... } }

This is the way stringstream was designed to be used. (Also: do you really want a stringstream, or just an ostringstream?)

answered Jun 16, 2011 at 10:23

James Kanze

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2 Comments

bdelmas Over a year ago

I use it here to change a float in a string and put this string in a big other string. What is the best to do that? And if I put std::stringstream ss; in a loop it will creat many ss in the RAM no?

James Kanze Over a year ago

std::ostringstream ss; ss << theDouble; theString += ss.str(); And if the stringstream is in the loop, there will still only be one in memory at a time.

jonsca · Accepted Answer · 2011-06-16 10:44:40Z

7

Set ss.str(""); when you want to clear out the excess characters (Edit: thank you).

Use .clear() if your stream has set any error flags in the process of the prior conversion.

edited Jun 16, 2011 at 10:44

answered Jun 16, 2011 at 10:20

jonsca

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5 Comments

Naszta Over a year ago

It is usually not enough. You should also use seekp(0) and seekg(0), too.

jonsca Over a year ago

@Naszta I was able to do it without the seekp/seekg portion after setting the string and then clearing the stream.

Naszta Over a year ago

@jonsca: in this case it depends on the implementation. I had many issue on it before. (I develop multi platform, I don't remember which implementation had/has this issue.)

csl Over a year ago

For future reference, this is covered in Scott Meyers books on C++ (which I recommend).

Naszta Over a year ago

@csl: Effective C++, More effective C++ and Effective STL in Amazon and the full book of Effective STL in China.

Naszta · Accepted Answer · 2011-06-16 10:49:14Z

If you use C++0x:

ss.swap(stringstream());

Visual Studio 2010 (SP1) supports it.

If you don't use C++0x:

ss.seekp(0); ss.seekg(0); ss.str(""); ss.clear();

It won't clear the memory, but you could use your stringstream object as it would be empty before.

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