**pointer explanation, please for a C++ programmer

[tms43]

I have this code, and I need to understand it better. I'm hoping one of you will explain, ESPECIALLY the part using the double pointer:

typedef strudt{    // I get this part, I include it because it might help with the rest
     float x, y; 
     float z;
     flozt r, g, b;
} Vert;

typedef struct {
     int n;
     Vert *verts;  //ok, this is for an array of verts
}Poly;

// ~~~~here is where I'm a little confused: ~~~
Poly *readPoly(FILE *f){  //how do I use this in main, or what would it look like in C++?
	int i;
	Poly *poly = (Poly *) malloc(sizeof(Poly));  //dynamic allocation of an array?
	fscanf(f, "%d", &poly->n);   //c version of reading in a file?
	poly->verts = (Vert*) malloc(poly->n*sizeof(Vert));  //another dynamic allocatin of an array?
	for(i=0; i< poly->n; i++)
		fscanf(f, "%f %f %f %f %f %f", &poly->verts[i].x, &poly->verts[i].y /*etc?*/ ); 
	return poly;
}

//ok, here is main:
int main(void){

	int i, numPolys;               // total number of poly's

	Poly **polys;                  //array of polys   ... I don't understand pointers to pointers

	scanf("%d", &numPolys);  //c stuff is so weird to me

	polys = (Poly **) malloc(numPolys*sizeof(Poly*));   //why make another array here?

	for (i = 0; i < numPolys; i++)  //start reading in the files, correct?
		polys[i] = readPoly(f);  // f should be declared as the file name, correct?  because it gives an error now
		return 0;

}

I'm trying to understand the entire part from Poly *readPoly(FILE *F){ ... on. C programmers write input files differently, and I've been looking in a C book that isn't very helpful with this particular style of writing C code. I know it looks basic for C programmers, but it doesn't look baisc for a C++ programmer.

Thank you for your patience

[Sebastiani]

fyi, there really isn't anything there that a c++ programmer wouldn't be expected to understand (aside from C API calls - which could be looked up with a little effort). the readPoly function reads a single polygon from the current position of a given file (look into fopen() and related functions) and returns a pointer to the allocated memory. so to have an array of them you need an array of pointers to polygons. using typedefs:

typedef Poly * poly_p;
typedef poly_p * poly_p_array;

[cpjust]

Poly **polys;

This is a pointer to a pointer. So the first malloc() allocates an array of pointers to Poly's, then the malloc() in readPoly() allocates the actual Poly structs.

[dwks]

Here's a tutorial on standard C file I/O: http://www.cprogramming.com/tutorial/cfileio.html

[tms43]

Thank you