macOS Will I ever understand array pointers?

[farmerdoug]

float *y, *ys;
int j;
if ((ys = (float *)calloc(points*points,sizeof(float))) == NULL)
		printf("ys\n");
if ((ys1 = (float *)calloc(points,sizeof(float))) == NULL)
		printf("ys1\n");
...
memcpy[ys[i*points],ys1,j*sizeof(float)];  // line  220

2dspline.c:220: error: subscripted value is neither array nor pointer

At least I remembered (evidentually) to declare and calloc ys as a *float not **float.

 

[robbieduncan]

Your memcpy is using [] instead of () to surround the arguments to the function.

Also you declare y and ys but then use ys and ys1.

 

[ChOas]

ys[i*points] indexes ys at i*points, since ys is a pointer to floats that would be a float.

You can't memcpy to a float.

That explains the error.

Now, for what you actually want to do: I have no clue.

-edit-

Oh, or what Mr. Duncan said there.

 

[farmerdoug]

pointers

thanks, I don' t think there is enough coffee in the world to wake me up. Also, the variables are defined somewhere. At least I got that right.

 

[farmerdoug]

Chaos

That might have something to do with it. There are work around, like loops for assigning things one at a time. Also assigning pointers
p[0] = *y[0] or something similar.

 

[farmerdoug]

memcpy should work for a float

Why not?

 

[robbieduncan]

memcpy documentation says:

void *memcpy(void *s1, const void *s2, size_t n);

The memcpy() function copies n bytes from the object pointed to by s2 into the object pointed to by s1.

So if s1 is a float rather than a pointer then it won't work.

 

[farmerdoug]

this compiled

float **ys, *ys1;


if ((ys = (float *)calloc(points,sizeof(float))) == NULL)
		printf("ys\n");
		
if ((ys1 = (float *)calloc(points,sizeof(float))) == NULL)
		printf("ys1\n");

	for (i = 0; i < points; i ++)
		{
	
		if ((ys[i] = (float *)calloc(points,sizeof(float))) == NULL)
			printf("ys[i]\n");
		}

	 memcpy(ys[i], ys1, j*sizeof(float));

[code]

I used the **ys, not to make memcpy work, but as required by Numerical Recipies in C.

 

[ChOas]

That might have something to do with it. There are work around, like loops for assigning things one at a time. Also assigning pointers
p[0] = *y[0] or something similar.

That copies the content of what y[0] is pointing to to p[0], This only works if y is a pointer to an array of pointers.

When I say 'works' I mean that it does what you mean it to do, it might still compile otherwise but it most certainly won't do what you expect

 

[ChOas]

You might want to have at these tutorials:

http://pweb.netcom.com/~tjensen/ptr/cpoint.htm
http://augustcouncil.com/~tgibson/tutorial/ptr.html

 

[lloyddean]

farmerdoug, I'd also recommend you take the time to look over this web page covering "Macro Pitfalls"