how can i copy one struct into another?

[Adam Rinkleff]

I have two structs

struct boardstate{
	int board[9][9];
	int wpawns, wknights, wbishops, wrooks, wqueens, wkings;
	int bpawns, bknights, bbishops, brooks, bqueens, bkings;
	int wkcastle, wqcastle, bkcastle, bqcastle; 
	int drawcounter;
	int legalmoves;  
	int wenpassant[2], benpassant[2]; //[0]=i; [1]=j
	int whitekcastle, whiteqcastle, blackkcastle, blackqcastle;
	int wkingloc[2], bkingloc[2];
	char absoluteboard[9][9]; //used to record pieces which cannot move due to absolute pins
	int dangerboard[9][9]; //used to record squares which the king cannot move to
	int reversedangerboard[9][9]; //used to record squares which the non-moving king cannot move to
	int allpossiblemoves[65][65]; //lists all possible move targets [y] for piece at square [x], equal to value of piece at [x]
	int allpossiblepositions[65][65]; //lists all possible move targets [y] for piece at square [x], equal to value of position at p[z]
	int wincheck; int bincheck;
	enum whoseturn color;
	int turn;
	double evaluation;
	double bestmoveeval;
	int loci, locj, targeti, targetj; //records to-from squares for piece which just moved
}; 


extern struct boardstate p[100];
extern struct boardstate X;

I want to make a copy of p[0], which is why I created X. Is there a way to copy everything from p[0] into X, or do I have to transfer each variable independently? Somewhere I read that memcopy might somehow do this, but I haven't seen anything which shows the necessary syntax.

[quzah]

memcpy will do the trick if you don't want to use the assignment operator. Note that it won't actually copy the contents of things pointed at, rather it would duplicate the contents of the pointer (make them point to the same space).

I read that memcopy might somehow do this, but I haven't seen anything which shows the necessary syntax.

You mean that you were too lazy to look up the memcpy function to see how to use it?


Quzah.

[Adam Rinkleff]

But how do I use memcpy? I can see on C++ Reference that it is of the format:

void * memcpy ( void * destination, const void * source, size_t num );

But what do I actually type? For example... size_t num? I don't know what that is. So how do I actually use it to copy from p[0] to X?

[Adam Rinkleff]

You mean that you were too lazy to look up the memcpy function to see how to use it?


Quzah.

No...I mean I don't understand how to use memcpy, because I've never used it before.. Of course I've looked it up, obviously I have, which is why I've mentioned it. Clearly I put some effort into this before coming here and asking about it. But no, I don't know how to use it. That's why I asked.

I really don't see why you have to be so rude. I'm trying to learn something, which means I don't already know the answers. If you want to help, thanks, great. If not, please refrain from being rude. I'm obviously asking how to use memcopy to copy [0] into X; either you know or don't. I'm asking for help, but I don't need to be harassed about being too "lazy" to figure it out. If I was lazy, I wouldn't be trying to figure it out.

[AndrewHunter]

You may want to take a look at the sizeof() function for that.

[CommonTater]

No...I mean I don't understand it. Yes, I've looked it up, obviously I have, which is why I've mentioned it. No, I don't know how to use it. That's why I asked. I really don't see why you have to be so rude. I'm trying to learn something, which means I don't already know the answers. If you want to help, thanks, great. If not, please refrain from being rude. I'm obviously asking how to use memcopy to copy [0] into X; either you know or don't. I'm asking for help, but I don't need to be harassed about being too "lazy" to figure it out. If I was lazy, I wouldn't be trying to figure it out.

Welll ... you could type something like .... memcopy(target, source, sizeof(target));

target being th name of the struct you are copying to and source being the one you are copying from ... and yes, they do have to be the same size.

You might also consider giving your variables more descriptive names than p and X...

[Adam Rinkleff]

sizeof(p[0]) is 35024, is that the size of the structure regardless of the values within it, or do those change?


Should I just do:

memcpy ( X, p[0], sizeof(p[0]));

?

Yah I guess that should work, sizeof(X) is also 35024. Thanks.

[CommonTater]

sizeof(p[0]) is 35024, is that the size of the structure regardless of the values within it, or do those change?


Should I just do:

memcpy ( X, p[0], sizeof(p[0]));

?

Well, gosh... why don't you give that a try and let us know if you run into trouble...
(IOW... a little confidence is often a very good thing.)

[Adam Rinkleff]

I did try it:


incompatible type for argument 1 of `memcpy'
incompatible type for argument 2 of `memcpy'

[AndrewHunter]

Or you could just do:

# include <stdio.h>
# include <string.h>

int main(void){

	struct myStruct{
		int a;
		int b;
	};
	myStruct myStructA;
	myStruct myStructB;

	myStructA.a = 5;
	myStructA.b = 6;

	myStructB = myStructA;

	printf("%d %d", myStructB.a, myStructB.b);

	getchar();
	return(0);
}

Look, everyone here means well. Sometimes people just come across short and to the point. Sarcasm and jokes are hard to implement through messages. My advice for all future endeavors is not to take anything personally and just look for the advice given. Trust me, there is plenty to learn from the people here, even if it comes across somewhat curt.

[Adam Rinkleff]

X=p[0];

That seems a lot easier, why then would I ever want to use memcpy instead of that?

[CommonTater]

I did try it:


incompatible type for argument 1 of `memcpy'
incompatible type for argument 2 of `memcpy'

Did you look at the instructions for memcpy() again?

You will note that it needs pointers...

memcpy(&X, &p[0], sizeof(p[0]));

[CommonTater]

That seems a lot easier, why then would I ever want to use memcpy instead of that?

Once again... go ahead and give it a try...

[Adam Rinkleff]

memcpy(&X, &p[0],sizeof(p[0]);

Oh, I was trying *X, *p[0], but going back to post #10 -- why use memcpy at all if I can just use what AndrewHunter suggested?

[AndrewHunter]

That would be because memcpy's arguments expect pointers and not objects. So you would implement it:

memcpy(&x, p, sizeof(p[0]));