C / C++ / MFC

9-Feb-06 13:45

I am a great fan of MFC's CString class, especially it's Format member function. Makes things so easy. But I now have a problem that requires me to use a strstream buffer in a loop. How do I go about reinitializing the strstream so that I write to the beginning of the buffer at each loop iteration. This code does not work, the string in the stream does not change at all after the first iteration (stays at "%%1")

ostrstream stream;
for (x = 1; x < 10; ++x)
{
   stream.seekp(0);
   stream << "%%" << x << ends;
...
}

This code however does work

for (x = 1; x < 10; ++x)
   ostrstream stream;
   stream << "%%" << x << ends;
...
}

Recreating the strstream in each loop iteration seems like a silly way to get this to work.

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_anil_9-Feb-06 14:07

9-Feb-06 14:07

use stream.clear(); inside the loop.

PJ Arends9-Feb-06 14:20

9-Feb-06 14:20

Nope, still does not work. I tried clear() alone, clear() followed by seekp(), and seekp() followed by clear(). All the same result as before.

_anil_9-Feb-06 14:35

9-Feb-06 14:35

actually no need of clear also. your code is right.
I want to know how did you get to know that the output is wrong.
please give that part of code.
because every thing is going fine in my code.

PJ Arends9-Feb-06 15:00

9-Feb-06 15:00

cout << stream.str() << endl;

This line is added in the loop for debugging only. and the output is a series of identical lines "%%1". I also looked up the value in the debugger, used the second ostrstream c'tor where you can supply a char * buffer to be used as the stream and watched that buffer, etc. All have the same effect.

I am using VC6 SP6 with the Feb 2001 SDK if that makes any difference. I tried the code with VC7.0 but that was an even worse experience than with VC6, calling stream.str() results in an access violation at address 0x00000000.

Christian Graus is always saying how streams are the best thing ever, but I am having serious doubts about that Sigh | :sigh:

_anil_9-Feb-06 15:34

9-Feb-06 15:34

<code>ostrstream stream;
	for (int x = 1; x < 10; ++x)
	{
		stream.seekp(0);
		stream << "%%" << x << ends;
		CString str = stream.str();
	}
</code>

In the above code I am getting str value %%1, %%2 and so on...
I don't know why you have the problem.

Regards
Anil

PJ Arends9-Feb-06 15:42

9-Feb-06 15:42

#include <iostream>
#include <strstream>

using namespace std;

int main(int argc, char* argv[])
{
    unsigned x;
    ostrstream stream;
    for (x = 1; x < 10; ++x)
    {
        stream.seekp(0);
        stream << "%%" << x << ends;
        cout << stream.str() << endl;
    }

	return 0;
}

output is 9 lines of %%1

I rebooted my computer, created a new project just to test this and yet I still get the same result. Oh well, I guess I will go back to the inefficient way that works for me.

Thanks for your attempt to help.

_anil_9-Feb-06 15:56

9-Feb-06 15:56

Yes I got the solution but don't know the reason.
in VC6 you have to include #include <strstrea.h> instead of #include <strstream> I guess. The folloing code will work.

<code>
#include <iostream>
#include <strstrea.h>  // Hear is the change

using namespace std;

int main(int argc, char* argv[])
{
    unsigned x;
    ostrstream stream;
    for (x = 1; x < 10; ++x)
    {
	stream.seekp(0);
        stream << "%%" << x << ends;
	std::cout << stream.str() << endl;
    }

	return 0;
}
</code>

Regards
Anil

PJ Arends9-Feb-06 16:15

9-Feb-06 16:15

Ok, mystery solved. The older version of strstream as declared in strstrea.h does not call freeze() which is why the code worked for you.

Thanks for your help Big Grin | :-D

Got it!

PJ Arends9-Feb-06 15:53

9-Feb-06 15:53

#include <iostream>
#include <strstream>

using namespace std;

int main(int argc, char* argv[])
{
    unsigned x;
    ostrstream stream;
    for (x = 1; x < 10; ++x)
    {
        stream.seekp(0);
        stream << "%%" << x << ends;
        cout << stream.str() << endl;
        stream.rdbuf()->freeze(false);
    }

	return 0;
}

stream.str() calls freeze(true) to lock the buffer, I have to call freeze(false) to unlock it. Why your code worked without it is a mystery to me.

HELP NEEDED HERE. PLEASE ANYONE!!!!

Bernhard9-Feb-06 19:51

Bernhard

9-Feb-06 19:51

This should work too...

stream.str() = "";

But as you had another solution, nevermind.

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-- modified at 1:52 Friday 10th February, 2006

jermzypeter9-Feb-06 13:00

jermzypeter

9-Feb-06 13:00

write a program that stored the total cost of 4 items in a grocery
store.

a. write a function to input the total cost into the array. the cost
entered should always range between 20000 and 40000.(check this
condition)

b. write a funcion to output the details.

* calculate the GCT for each item. (Note :-GCT is 20% of Total
cost). Also calculate the Net cost of each item (Note: -Net cost =
Total cost - GCT)

* finally print the Total Cost, GCT and Net Cost in a proper
tabular format.

please anyone.. your help is needed... any help is appreciated,..
thank you....

peter burnett. "the maestro"

George L. Jackson9-Feb-06 13:12

George L. Jackson

9-Feb-06 13:12

You should ask a specific question! What have you done to solve these problems? Are you new at programming?

jermzypeter9-Feb-06 13:18

jermzypeter

9-Feb-06 13:18

ok. thanks for replying. and yes i'm new at programming. its my 2nd week in class and i dont really understand the whole basic thing of c++. thats why i would like someone to at least do that question and i'll try and understand it.

peter burnett. "the maestro"

George L. Jackson9-Feb-06 13:25

George L. Jackson

9-Feb-06 13:25

You won't learn anything unless you actually try to solve the problems yourself. People will help you more if you attempt to solve it on your own.

jermzypeter9-Feb-06 13:33

jermzypeter

9-Feb-06 13:33

thats true.. i think i would have a better knowledge of the subject if i understood the basics more. thaz my main problem. and i really like the whole topic of programming. i just want to understand it more and more. thats why i'm trying to get as much help as i can.

peter burnett. "the maestro"

Lord Kixdemp9-Feb-06 13:37

Lord Kixdemp

9-Feb-06 13:37

Look, just try it on your own, and when you get stuck with something, look on Google for that part that you got stuck on... If you don't find anything, then come here and ask us. That's what I do, and it works! Wink | ;-)

Lord Kixdemp
www.SulfurMidis.com
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