Dynamically assigning data type

[yogi]

Hi guys,
I'm trying to write a program that will read in a series of files and
create a 3D array from the files read in for converting 2D images to 3D
objects. The values read in will be considered as pixel colours and the
size that 1 pixel occupies will depend on an input from the user when
running the program. How can I dynamically change the data type of my 3D
array at runtime. eg. 3D array was defined as type unsigned char in the
code but the file to be read requires the array to be type unsigned short.
I've tried using

typedef unsigned char pixeltype; // assuming data is unsigned char

in my header file and then writing all my functions using the type
pixeltype.
I've tried casting the pointer to the array to a variable of type
unsigned short but it didn't really work. Googling also didn't produce
anything fruitful. Thanks and best regards.

Yogi

[Malcolm]

"yogi" <le******@tartarus.uwa.edu.au> wrote

How can I dynamically change the data type of my 3D
array at runtime.

unsigned char *image; /* your raw data */

int pixelsize; /* size of each pixel, in bytes */
int redoffset; /* offset of the start of the red channel from pixel
beginning */
int redbits; /* number of bits used for the red channel */

For extra brownie points, you can have a big / little endian flag.

[Richard Bos]

yogi <le******@tartarus.uwa.edu.au> wrote:

I'm trying to write a program that will read in a series of files and
create a 3D array from the files read in for converting 2D images to 3D
objects. The values read in will be considered as pixel colours and the
size that 1 pixel occupies will depend on an input from the user when
running the program. How can I dynamically change the data type of my 3D
array at runtime. eg. 3D array was defined as type unsigned char in the
code but the file to be read requires the array to be type unsigned short.

That's not really possible. If you've only allocated memory for a
certain number of chars, however are you going to fit the same number of
shorts in there? It would mean that sizeof(short) <= sizeof(char), and
that is only very rarely true on desktop computers. (And where it is, of
course, sizeof(short) == sizeof(char) == 1, and CHAR_BIT >= 16.)

If you know the maximum size of your elements, going the other way
(allocating memory for an array of the largest possible data type, and
then possibly filling it with a smaller type) is possible, but may cost
a lot of memory.

Richard

[yogi]

Yeah... I guess I might have to do it that way by using unsigned short
in my code and then cast it to chars as I need to. Thanks for the help.
Cheers!

Richard Bos wrote:

yogi <le******@tartarus.uwa.edu.au> wrote:

I'm trying to write a program that will read in a series of files and
create a 3D array from the files read in for converting 2D images to 3D
objects. The values read in will be considered as pixel colours and the
size that 1 pixel occupies will depend on an input from the user when
running the program. How can I dynamically change the data type of my 3D
array at runtime. eg. 3D array was defined as type unsigned char in the
code but the file to be read requires the array to be type unsigned short.

That's not really possible. If you've only allocated memory for a
certain number of chars, however are you going to fit the same number of
shorts in there? It would mean that sizeof(short) <= sizeof(char), and
that is only very rarely true on desktop computers. (And where it is, of
course, sizeof(short) == sizeof(char) == 1, and CHAR_BIT >= 16.)

If you know the maximum size of your elements, going the other way
(allocating memory for an array of the largest possible data type, and
then possibly filling it with a smaller type) is possible, but may cost
a lot of memory.

Richard