storing structs with bit-fields on disk minimally

[theperplepigg]

Here's my problem :

i have a structure, defined as follows:

#define MAPSIZE 14
struct node
{
	unsigned short leftMap		:MAPSIZE;		// map to left input
	unsigned short rightMap		:MAPSIZE;		// map to right input
	unsigned short leftValue	:1;			// left value  = 0 || 1
	unsigned short rightValue	:1;			// right value = 0 || 1
	unsigned short out		:1;			// output of node
};

(yes, i know i still have 1 bit to play with, just don't need it)

and an array of these nodes. i want to be able to store this array on disk in just as little space as i do in memory(32 bits*numNodes). is there any slick way to write/read it, such as

nodes[i] >> out; // to write
out >> nodes[i]; // to read

or do i have to go about writing read/write functions that will pack an unsigned short and write that to disk? thanks.

--paul

[cup]

You don't have to unpack it into an unsigned long (not short): just use a union.

union
{
    struct node
    {
	unsigned short leftMap		:MAPSIZE;		// map to left input
	unsigned short rightMap		:MAPSIZE;		// map to right input
	unsigned short leftValue	:1;			// left value  = 0 || 1
	unsigned short rightValue	:1;			// right value = 0 || 1
	unsigned short out		:1;			// output of node
    } bitty;

    unsigned long holy;
} nodes[NODE_MAX];

out << nodes[i].holy;  // to write
out >> nodes[i].holy;  // to read

[cup]

If you want to use as little space as possible, use the C routines fopen, fread, fwrite and fclose. Then a 32 bit word will only take up 32 bits. C++ isn't very good for binary input.

[theperplepigg]

thanks, i will try your suggestions. this isn't an issue just yet, but i was thinking about it, since it'll come up next week sometime when i do that part of the program.

--paul