BTW, for bitting (ok mischosen term...), I always cast my integers either long or short... Rarely I use the "int" keyword because I want to keep a control over that kind of problem. Though most of the computers nowadays take 32-bits integers, sometimes I prefer to put short integers (when I''m having values that cannot pass through 65535). But almost all of the time I use simple long values, because anyway the processors handle them in one cycle. That was my two cents.

(( Applaud Toto, Tata and Popo who came handly once again for a wonderful example ))

Programming is:A.The art of debugging a blank sheet of paper (or an empty file).B.A pastime similar to banging one's head against a wall, but with fewer opportunities for reward.C.The most fun you can have with your clothes on (although clothes are not mandatory).

hey, thanks for all the help everyone. eventually i figured out what my problem was on my own last night, it seemed i was doing something wrong when i was checkin for status of a bit. look at this:

if(TileBits &= 1<i had that equal sign in there and it was setting the bit rather than checking it...  geez i feel dumb...  oh well, that''s just part of the game, i guess...thanks,david    

Poltras: You can have the compiler pack it to whatever size you wish, and you should even be able to use 2 bits. Use the compiler-specific packing preprocessor commands. VC uses #pragma pack. You can also pad it manually if you wish -- that's part of C++. Here is a console app that shows the alignment:

        #include "stdafx.h"#include <iostream>using namespace std;#pragma pack(push)struct flags_2{	bool hardware : 1;	bool does_3D  : 1;	// no padding};#pragma pack(pop)struct flags_8{	bool hardware : 1;	bool does_3D  : 1;	char : 0; // pads to char alignment};struct flags_16{	bool hardware : 1;	bool does_3D  : 1;	short : 0; // pads to short alignment};struct flags_32{	bool hardware : 1;	bool does_3D  : 1;	long : 0; // pads to long alignment};struct flags_optimal{	bool hardware : 1;	bool does_3D  : 1;	int : 0; // pads to int alignment};int main(int argc, char* argv[]){	// sizeof doesn't work with bitfields;	// the smallest quantity it can return	// is sizeof(char) or one byte	cout << "flags_8 takes up " << sizeof(flags_8) << " bytes" << endl;	cout << "flags_16 takes up " << sizeof(flags_16) << " bytes" << endl;	cout << "flags_32 takes up " << sizeof(flags_32) << " bytes" << endl;	cout << "flags_optimal takes up " << sizeof(flags_optimal) << " bytes" << endl;	return 0;}        

- null_pointer
Sabre Multimedia


Edited by - null_pointer on June 19, 2000 8:54:06 AM

hmm...I guess the smallest unit is 1 byte. If you use C++ bitfields, then you can choose your padding according to your needs.

To go about reading/writing bits to a file (like you would in a compression program), you hold a cache (like 4 ints?) and cache the bit read/write operations until they fill up the ints and then read/write the ints to disk. In C++, you can also do unions if you like to make the code more readable:

    #include <iostream>using namespace std;// make the code more readableconst bool on  = 1;const bool off = !on;// use a packet of 32 bitsunion packet{	unsigned long number;	struct	{		unsigned char bit_01 : 1;		unsigned char bit_02 : 1;		unsigned char bit_03 : 1;		unsigned char bit_04 : 1;		unsigned char bit_05 : 1;		unsigned char bit_06 : 1;		unsigned char bit_07 : 1;		unsigned char bit_08 : 1;		unsigned char bit_09 : 1;		unsigned char bit_10 : 1;		unsigned char bit_11 : 1;		unsigned char bit_12 : 1;		unsigned char bit_13 : 1;		unsigned char bit_14 : 1;		unsigned char bit_15 : 1;		unsigned char bit_16 : 1;		unsigned char bit_17 : 1;		unsigned char bit_18 : 1;		unsigned char bit_19 : 1;		unsigned char bit_20 : 1;		unsigned char bit_21 : 1;		unsigned char bit_22 : 1;		unsigned char bit_23 : 1;		unsigned char bit_24 : 1;		unsigned char bit_25 : 1;		unsigned char bit_26 : 1;		unsigned char bit_27 : 1;		unsigned char bit_28 : 1;		unsigned char bit_29 : 1;		unsigned char bit_30 : 1;		unsigned char bit_31 : 1;		unsigned char bit_32 : 1;	};};int main(int argc, char* argv[]){	packet my_packet;	// use it like a long	my_packet.number = 5890327;	// access the individual bits	my_packet.bit_01 = off;	my_packet.bit_07 = on;	my_packet.bit_27 = on;	cout << "my_packet = " << my_packet.number;	return 0;}    

- null_pointer
Sabre Multimedia

OK, first the output filename and input filename are different (probably just a typo). Second, the file you are writing is in text mode, so I think you must append an endl to the file when you write it out, like this:


output_file << bitfield_write.bits << endl;



It reads and writes fine now.

Good Luck!




- null_pointer
Sabre Multimedia