How do I make a combat msg buffer?

**pliang** · 04-10-2005

The game I am working on is a text console game. I am having some trouble implementing the combat messages. I intend to have 4 lines of combat messages showing on the screen, the newest message would be pushed in at the bottom of the combat message box and effectively popping out the oldest message on the top. I think I know how to do that, I'll simply have 4 pointers and I will shift them up by one and have the pointer representing the newest line point to the new message string. So I am going to have a function that looks like

void DrawCombatMsg(char *text);

The argument would be the latest combat message, I don't know if passing it a cstring is the best way to do it but when I experimented with passing it a string class my compiler failed to recognize the function prototype in the header file

It whined something about the identifier not found.

But before I pass the latest combat message to my DrawCombatMsg() function I need to formulate the string (name of attacker, name of defender, hit or miss, how much damage). I have another function called

FormCombatMsg()

for that. Now this is where I am really confused. What kind of argument and return type should I put for FormCombat Msg function? Ideally I want it to return a string but the only way I know how to "form"(where I combine variables and strings) a string is by using cout and that that puts it directly to the standard output. So I guess my question is, is there a way that I can format a string and "save" it to another string so I can use it later on as an argument?

I experimented with the string class of the string library and ostringstream of the sstream library, none of them really worked for me, most likely because I didn't use them right. Please help.

**SirCrono6** · 04-10-2005

Maybe you were using stringstream wrong

First, include <sstream>. Let's say you create stringstream msg. Then you could pass a reference to a stringstream (msg) to FormCombatMessage:

Code:

void FormCombatMessage( stringstream &msg );
//...
stringstream msg;
FormCombatMessage( msg );

FormCombatMessage will fill it with info like a stream:

Code:

msg << Attack << " attacks " << Defender; //Etc.

Then, DrawCombatMsg would use your prototype (void DrawCombatMessage( char* text )), and you can pass the stringstream using:

Code:

DrawCombatMsg( msg.str().c_str() );

Then DrawCombatMsg does all that about the four messages and then outputs text. There you go

- SirCrono6

Edit: Shouldn't pass &msg, just msg.

Edit 2: To avoid confusion:

Code:

FormCombatMessage( stringstream &msg ); //Prototype
//...
FormCombatMessage( msg ); //Function call

**pliang** · 04-10-2005

The book I am reading tells me to use ostringstream. So instead of

Code:

void FormCombatMessage( stringstream &msg );

I did

Code:

void FormCombatMessage( ostringstream &msg );

Is that a problem? Also, the book tells me that using the str() method "freezes" the object, and I will no longer be able to write to it, does that mean the "msg" variable can only be used once in this case? Would I need to create it dynamically then if so?

**SirCrono6** · 04-10-2005

You should use stringstream instead of ostringstream. str() will not "freeze" the object (test this code):

Code:

#include <iostream>
#include <sstream>

void Msg( std::stringstream &Hello )
{
  int X = 10;
  Hello << X;
}

int main( void )
{
  std::stringstream Hello;
  Msg( Hello );
  std::cout << Hello.str().c_str() << std::endl;
  Hello << " 10";
  std::cout << Hello.str().c_str();
  std::cin.get();
  return 0;
}

/* Output -
10
10 10
*/

Also, see my edit (it's important).

- SirCrono6

**pliang** · 04-10-2005

Cool, thanks SirChrono! Now is there a way to write over the old string completely with new string or does whatever I add always get attached to the end of the original string? Also what's the difference between using stringstream and ostringstream?

**SirCrono6** · 04-10-2005

Ah, I've just found a way to clear the contents of a stringstream:

Code:

stringstream msg;
msg.str( string() );

There is a stringstream, ostringstream, and istringstream. I believe that they each lean towards either input or output (stringstream being neutral), but I'm not sure.

- SirCrono6

**Magos** · 04-11-2005

Originally Posted by SirCrono6

Ah, I've just found a way to clear the contents of a stringstream:

Remember to clear the flags also, or you might experience some troubles in some rare cases:

Code:

stringstream msg;
msg.str( string() );
msg.clear();

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