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double size array initialize ?

thefirstfbli
thefirstfbli asked
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Last Modified: 2012-08-14
i dont know size of the array orginally. it is double size array.

how to initialize it at the begining of the program ?
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Commented:
What's the maximum expected size?    

If it's less than a million or so, it's often simpler to just declare it to be that size.   That's assuming this is running on some reasonably modern computer with many megabytes of memory.

For larger sizes, use malloc:

double * Array;

Array = malloc( sizeof( double ) * TheActualSize );

\
....   use   Array here as usual.

free( Array );  // when you're done using the array.



Author

Commented:
expected size is not too big.

actually i want to learn its sense, logic.

i do it like above,

double *p;

p=(*double) malloc(sizeof(double) * what ? )

what is the actual size ?

and also, how can i reach the integer value @ point[1][2], if it is 8*8 array. like *(p+i) ? i is counter.
hi,

>>and also, how can i reach the integer value @ point[1][2], if it is 8*8 array. like *(p+i) ? i is counter.

That means you are using Two dimentional array,
double *p[];
p=(double *)malloc(size(double)*(8*8));
Through this you can allocate a two dimensional array.
you can assign the values as,
*(*(p+i)+j)=0.0  >>where i and j are two integers

i think this will help you

Deepu

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AxterSenior Software Engineer

Commented:
Check out the wrapper functions in the following links:
http://code.axter.com/allocate2darray.h
http://code.axter.com/allocate2darray.c

Author

Commented:
thanks deepudeepam , it is really good .

last thing about the line; " double *p[] " to understand,

double's is in the code because numbers can be large, right ? instead of double may i use int ?
and why we use *p[], not only *p ?

thanks so much.

AxterSenior Software Engineer
Commented:
>>instead of double may i use int ?

Yes

>>*p[], not only *p

In order to traverse a variable using two sets of brackets ([x][y]), you need a pointer of pointers.
You can do this by either of the following methods:
double *p[];
or
double **p;

I recommend using **, but that's a personal opinion.

If you use only a single dimesional variable type (*p), then you would need to add extra logic to your single bracket ([x]) to traverse a 2-dimensional buffer.

p[x + y * LenX] = 123;
AxterSenior Software Engineer

Commented:
Here's example for creating a buffer for a 2-D array:

void **Allocate2DArray(int TypeSize, int x, int y)
{
      void **ppi            = malloc(x*sizeof(void*));
      void *pool            = malloc(x*y*TypeSize);
      unsigned char *curPtr = pool;
      int i;
      if (!ppi || !pool)
      {  /* Quit if either allocation failed */
            if (ppi) free(ppi);
            if (pool) free(pool);
            return NULL;
      }

      for(i = 0; i < x; i++)
      {
            *(ppi + i) = curPtr;
            curPtr += y*TypeSize;
      }
      return ppi;
}



Example usage:
int **My2DChar = Allocate2DArray(sizeof(int), x, y);

Author

Commented:
ok.. that's all thanks..
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