[comp.lang.c++] iostream streambuf question

leo@atcmp.nl (Leo Willems) (08/18/90)

Can someone provide me with a small example of a derived class from
streambuf. It should have:

	1) a get area of 1 byte  (to fetch chars from i.e. wgetch() )
	2) a put area of ~20 bytes.
	3) the get and put areas are different arrays.
	4) overflow() only outputs the put area to cerr
	5) underflow() flushes, then fetches 1 character and returns.

I have this working under 2.0 iostream, but the same code fails to work
proparly on a different machine with 2.1 iostream. (different suppliers)
So I guess  my working example is just a case of bad luck :-(

If someone can help me with a small example, thanks!
For anybody who has some time left, here is the relevant part of the code,
I think only the constructor, overflow() and underflow() are interesting:

=======================

win.h:

#ifndef WINH 
#define WINH

#include <iostream.h>
#include "hwin.h"


class win : public streambuf  {
private:
	delta dy, dx;
	coord y, x;
	char s[5+1];	//put area
   	char geta[1];	//get area
	hwin *hwp
	int box;	// true if boxed
	int nodel;
protected:
	int underflow();
	int overflow(int c=EOF);
public:
	void move(coord, coord);
	void draw();	
	void undraw();
	void setsize(delta d_dy, delta d_dx){
		dy = d_dy; dx = d_dx;
	}
	void setcoord(coord c_y, coord c_x){
		y = c_y; x = c_x;
	}
	void setbox() { box = 1; }
	void setnodelay(int i) { nodel = (i!=0); }
	win();
	~win();
};

#endif /* WINH */




win.C:


#include "win.h"

int
win::underflow()
{
	// flush output
	if (pptr() && pptr() > pbase()) { overflow(EOF);}
	// reset get area
	setg(geta, geta, geta+1);

	if (!hwp) { setg(0,0,0); return EOF;}

	int c;
	c = hwp->cwgetch(nodel);

	if (c == EOF){
		setg(0,0,0);
		return EOF;
	}

	geta[0] = c;

	return zapeof(c);
}

void
win::move(coord y, coord x) {
	if(!hwp) return;
	overflow(EOF); hwp->cmove(y,x) ; 
}

win::win() : streambuf(s, sizeof(s)-2)
{
	setp(base(), ebuf()-2);
	setg(0,0,0);
	dy = dx = 0; y = x = 0; hwp = 0; box=0; nodel = 0;
}

win::~win()
{
	if (hwp) undraw(); 
}

void
win::draw()
{
	if (!hwp){
		hwp = new hwin(dy, dx, y, x, box);
	}
}

void
win::undraw() {
	if (hwp) {
		overflow(EOF);
		delete hwp;
		hwp = 0;
	}
}

int
win::overflow(int c)
{
	if(hwp) {	
		if(c == EOF){ *(pptr()) = 0; }
		else { *(pptr()) = c; *(pptr()+1) = 0; }
		hwp->caddstr(s);
	}
	setp(base(), ebuf()-2);
	
	return zapeof(c);
}	

Thanks


 Leo Willems			Internet: leo@atcmp.nl
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