Hello All, I know that C doesn't come with anysort of list functionality, but I have come towards a situation where a list would be really handy. Does anybody know any tricks? Thanks in advance.

I've come from OO languages like Java, C# and C++, I'm using C at the moment because I have been instructed to by my tutor, there's no getting out of it I'm afraid. I can write a list in OO languages easily enough. The only reason why I wouldn't initially use array over a list is a situation when the required dimenisons of the array are unknown, i.e. loading data in from a file.

I'm having a bit of nightmare implementing realloc


// Initialized in a loop somewhere else

vectors.refs = malloc(sizeof(Poly *));

// Later on

Poly* polyArr;

ptr.v1 = &vectors[poly[one]];
polyArr = (Poly *) ptr.v1->refs;
size = sizeof(Poly *)*(ptr.v1->refCount+2);
polyArr[ptr.v1->refCount] = ptr;
vectors[poly[one]].refs = realloc(vectors[poly[one]].refs, size); // Crashes here
ptr.v1->refCount++;

HEAP[gp.exe]: Heap block at 00933290 modified at 009332C0 past requested size of 28
Windows has triggered a breakpoint in gp.exe.



Believe me, I am trying to make it simple :)

Here's in essance what I'm trying to do:-


struct Vector
{
void * refs; // Needs to store Polys that have referenced this;
int refsCount;
};

struct Poly
{
Vector * vector;
};

struct Model
{
Poly * polys;
};

Vector vectors [10];

// Initialize Vectors
for(int i = 0; i < 10; i++)
{
vectors.refs = malloc(sizeof(Poly *));
vectors.refCount = 0;
}

Model someModel;
someModel.polys = malloc(sizeof(Poly*)*10);

Poly * ptr = someModel.polys;

for(int i = 0; i < 10; i++)
{
ptr->vector = vectors;
vectors.refs[vectors.refCount] = ptr; // Need to say what poly referenced it;
vectors.refCount++;
vectors.refs = realloc(vectors.refs, sizeof(*Poly))*vectors.refCount+1); // Need to resize refs incase another poly referecnes this vector

ptr++
}

Quote:Original post by DarkMatter2008

struct Vector{    void * refs; // Needs to store Polys that have referenced this;    int refsCount;};

Why are you using void? Are you going to have references to structs other than Poly? If not, forward declare Poly and use pointers to Poly. Also, you need to decide between arrays and linked lists here. The typical way of doing a linked list in C would be to add a "Poly *next;" to the Poly struct and then refs should be a pointer to the first Poly in the list. If you're using arrays, then you'll want refs to be a pointer to pointer to Poly (Poly **refs;) so that you can point to an array of Poly structs.

And, for what it's worth, // comments are only valid in C++ and C99 not C89.

Quote:

struct Poly{    Vector * vector;};

This shouldn't compile in C since you don't get the automatic typedef's. You should write:

typedef struct Poly_ Poly;strut Poly_ {    // ...};

You should actually put the typedef line before you define Vector to forward declare Poly for use in Vector.

Quote:
for(int i = 0; i < 10; i++)

Defining a variable in the for statement like this is, again, a feature of C++ and C99. If you're using C89 it shouldn't compile.

Quote:
vectors.refs = malloc(sizeof(Poly *));

It's generally a good idea to write:
var = malloc(sizeof *var);
since it's a bit more robust in the face of changing the type or typename of the variable var.

Quote:
Model someModel;

Mixing variable declarations with code is, again, only for C++ and C99, not C89.


Other than that, and a few typos, it compiles as C99 code, looks right (although it's a little strange to allocate for space+1 instead of allocating the +1 when you need it), and doesn't crash for me.