Calling all C-men Again

[DanKarron at UCBVAX.BERKELEY.EDU]

As promised, here is some sample code to demonstrate my problem.

My goal is to have a dynamically allocated array of pointers to the
base of an array of 3 floats and a dynamically allocated array of pointers
to the base of a 2x3 array of floats;

The results of compilation are at the end of the code. Cut out the
code and use this makefile defines:

CFLAGS = -g2 
LDFLAGS= -lmalloc

-------------snip.c------------------------------------------snip.c------------
/* The goal here is to construct a list of pointers to 
 * the base of an array of 3 float and the base of
 * a 2x3 array of floats */

#include "stdio.h"
#include "malloc.h"

typedef struct LineTag {
	float EndPoints[2][3];
	float PlaneNormals[2][3];
	char LineName[100];
	} Line;

typedef struct PointTag {
	float Vertex[3];
	char PointName[100];
	} Point;

typedef struct WrapperTag {
	Line *LinePointer;
	Point *PointPointer;
	} Wrapper;

main()
{
Wrapper *p,*q,*r;
float (**plane_list)[2][3];
float (**point_list)[3]; /* why so much indirection ?*/

printf("sizeof **plane_list=%d\n",sizeof(**plane_list)/sizeof(float));
printf("sizeof **point_list=%d\n",sizeof(**point_list)/sizeof(float));

plane_list=calloc(3,sizeof(float *)); /* how do you spec a pointer to an array ? */
point_list=calloc(3,sizeof(float *)); /* make three slots at this address for demo */
p=calloc(1,sizeof(Wrapper));

p->PointPointer=calloc(1,sizeof(Point));
point_list[0]= p->PointPointer->Vertex; /* put the base address of the vertex list at point_list slot 0 */
printf("p->PointPointer=%#x\n",point_list[0]); /* the addresses match... */
printf("point_list[0]=%#x\n",point_list[0]);

p->PointPointer->Vertex[0]=0.1; /* assign some values */ 
p->PointPointer->Vertex[1]=0.2; /* we should see the same values from point_list */
p->PointPointer->Vertex[2]=0.3;

printf("%d:(%#x)%f,(%#x)%f,(%#x)%f\n",0,&p->PointPointer->Vertex[0],p->PointPointer->Vertex[0],
	&p->PointPointer->Vertex[1],p->PointPointer->Vertex[1],
	&p->PointPointer->Vertex[2],p->PointPointer->Vertex[2]); /* verify addresses and values */

printf("%d:(%#x)%f,(%#x)%f,(%#x)%f\n",0,
	&((*point_list[0])[0]),(*point_list[0])[0],
	&((*point_list[0])[1]),(*point_list[0])[1],
	&((*point_list[0])[2]),(*point_list[0])[2]); /* Huh ?? */
 

/* you fill in the rest */

p->LinePointer=calloc(1,sizeof(Line));
plane_list[0]=p->LinePointer->PlaneNormals;
p->LinePointer->PlaneNormals[0][0]=0.0;
p->LinePointer->PlaneNormals[0][1]=1.0;
p->LinePointer->PlaneNormals[0][2]=2.0;
p->LinePointer->PlaneNormals[1][0]=10.0;
p->LinePointer->PlaneNormals[1][1]=11.0;
p->LinePointer->PlaneNormals[1][2]=12.0;

q=calloc(1,sizeof(Wrapper));
q->LinePointer=calloc(1,sizeof(Line));
q->LinePointer->PlaneNormals[0][0]=100.0;
q->LinePointer->PlaneNormals[0][1]=101.0;
q->LinePointer->PlaneNormals[0][2]=102.0;
q->LinePointer->PlaneNormals[1][0]=1010.0;
q->LinePointer->PlaneNormals[1][1]=1011.0;
q->LinePointer->PlaneNormals[1][2]=1012.0;

r=calloc(1,sizeof(Wrapper));
r->LinePointer=calloc(1,sizeof(Line));
r->LinePointer->PlaneNormals[0][0]=0.10;
r->LinePointer->PlaneNormals[0][1]=1.10;
r->LinePointer->PlaneNormals[0][2]=2.10;
r->LinePointer->PlaneNormals[1][0]=10.10;
r->LinePointer->PlaneNormals[1][1]=11.10;
r->LinePointer->PlaneNormals[1][2]=12.10;

}
--cut.c-here-------------------------------------------------------------------
Here is what the compiler says:
karron:~/D.Bug:47make Bug
        cc -g2  Bug.c -lmalloc -o Bug
ccom: Warning: Bug.c, line 38: Illegal pointer combination:  pointer to array of
 float  versus  pointer to float
      point_list[0]= p->PointPointer->Vertex; 
      --------------------------------------^
ccom: Warning: Bug.c, line 59: illegal array size combination
      plane_list[0]=p->LinePointer->PlaneNormals;
      ------------------------------------------^
karron:~/D.Bug:48Bug
sizeof **plane_list=6
sizeof **point_list=3
p->PointPointer=0x10006a10
point_list[0]=0x10006a10
0:(0x10006a10)0.100000,(0x10006a14)0.200000,(0x10006a18)0.300000
0:(0x10006a10)0.100000,(0x10006a14)0.200000,(0x10006a18)0.300000
Exit 200



What do you think it the way to do this ? I want to use arrays, not
float ***plane_list. Why ? Because the 2x3 array and the 1x3 array is
being used as a basic geometric object, and I want to be able to
print out the values in the debugger as a unit. My subroutines take
this 2x3 array as a basic unit, similar to the sgi typedef Matrix, which
is a 4x4 array of floats. Passing anything else should signal a compiler
error with prototype checking turned on. You can pass a float *, 
but I want stronger typeing than that.

Cheers!


Dan.
| karron at nyu.edu (e-mail alias )         Dan Karron, Research Associate      |
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