Memory allocation for structures

[camelxl]

Hi all,

I need some help. Could somebody please tell me what is wrong with this code, or maybe suggest a better way to do this.

typedef struct {
long Size;
double Data[1];
} Struct2;
typedef Struct2 **Struct2Hdl;

typedef struct {
double f0;
double df;
Struct2Hdl Array;
} Struct1;

int main (void)
{
Struct1 *Data;

/* Allocate memory for Data structure
Data= (Struct1 *) malloc(sizeof(Struct1));
/* Allocate memory for Array handle
(*Data).Array = (Struct2**)malloc(sizeof(Struct2));
/* Allocate memory for Size element of Array hanle
(*(Power)->Array)->Size = (long*)malloc(sizeof(long));

When i compile i get the following error due to the last line:

error C2440: '=' : cannot convert from 'long *' to 'long'

I know malloc will return a 'long *' but how do i allocate memory to 'Size' and 'Data'

How do i allocate memory for the elements of the structures. If i don't allocate memory i get an 'Unhandled exception error'. Or is there a better way to allocate memory for these complicated structures. Do i have to allocate memory for each elemnt in the structure and what if one of the elements is itself a handle to another structure. How do i allocate memory for it

Thanks

 

[PerFnurt]

The code looks very c-ish. If it actually is c++ I'd recommend c++ify it:
Initialize the structs through constructors.
Perhaps even use classes rather than structs.
Don't use c-style cast.
Use STL (a std::vector perhaps?).
Use new not malloc





/Per
[sub]
"It was a work of art, flawless, sublime. A triumph equaled only by its monumental failure."[/sub]

 

[ArkM]

Compiler is right:

/* Allocate memory for Size element of Array hanle (????)...
  (*(Power)->Array)->Size = (long*)malloc(sizeof(long));

It seems Size is long, but you assign a pointer to it...
That's all.

 

[camelxl]

PerFunt:
Could you explain how to use 'new' in this case because i get the same thing when i try it.

ArkM:
If i do it like this:-
(*(Power)->Array)->Size = (long)malloc(sizeof(long));

i get an "Unhandled exception" error.

 

[Clairvoyant1332]

You shouldn't be using that last malloc at all. The only time you should be allocating memory is if you have a pointer to a data structure.

I think part of your problem is that you're declaring Struct2Hdl as Struct2 ** instead of Struct2 *. I don't see why you would need a double pointer.

 

[ArkM]

camelxl:
I don't consider that allocation is OK at all. We don't know what's Power pointer, we allocate a slot for one long only, then save pointer as a size...
Struct2:ata must be a pointer, not an array. C-like allocation for array of n elements must be malloc(n*sizeof(ElementType)), etc...
Keep it simple...

 

[mingis]

typedef struct {
long Size;
double Data[1];
} Struct2;
typedef Struct2 *Struct2Hdl;

typedef struct {
double f0;
double df;
Struct2Hdl Array;
} Struct1;

int main (void)
{
Struct1 *Data;

/* Allocate memory for Data structure
Data = (Struct1 *)malloc(sizeof(Struct1));
/* Allocate memory for Array handle
Data->Array = (Struct2*)malloc(sizeof(Struct2));
/* element Size does not need allocation - it is allready allocated in previous statement
Data->Array->Size = SOME_SIZE;