"data hiding" prototype code

[sofeng]

I'm not sure if "data hiding" is the correct term, but I'm trying to
emulate this object-oriented technique. I know C++ probably provides
much more than my example, but I'd just like some feedback to find out
if I've done anything wrong. Also, I am working on this for an
embedded environment, so if there are great inefficiencies with this
code, I'd like to know that also. I realize there is overhead with
using an "accessor" function.

I'm trying to:
1.) "hide" data (variables declared as static at file scope) within a
file (algorithm.c)
2.) manipulate the data using an algorithm function (Algorithm())
3.) provide external access to the data using an "accessor" function
(GetAlgorithmDa ta())

Here is my code:

main.c:
#include <stdio.h>
#include "algorithm. h"

int main(void)
{
const ALGORITHM_DATA *alg_ptr;

Algorithm();
GetAlgorithmDat a(&alg_ptr);
/*alg_ptr->data1 = 99.9;*/ /* This is not allowed */
printf("%f\n", alg_ptr->data1);
printf("%f\n", alg_ptr->data2);
printf("%f\n", alg_ptr->data3);

return 0;
}

algorithm.c:
#include "algorithm. h"

static ALGORITHM_DATA alg;

void GetAlgorithmDat a(const ALGORITHM_DATA **out)
{
*out = &alg;
}

void Algorithm(void)
{
alg.data1 = 1.0;
alg.data2 = 2.0;
alg.data2 = 3.0;
}

algorithm.h:
#ifndef ALGORITHM_H_
#define ALGORITHM_H_

typedef struct {
double data1;
double data2;
double data3;
} ALGORITHM_DATA;

void GetAlgorithmDat a(const ALGORITHM_DATA **out);
void Algorithm(void) ;

#endif /*ALGORITHM_H_*/

[sofeng]

On Apr 11, 5:43 pm, "E. Robert Tisdale" <e...@netwood.n etwrote:

The C computer programming language supports encapsulation
but *not* data hiding (like the private label in C++).
C programmers have always used "opaque" data types
when they need to "hide" data.
This is accomplished by publishing a type declaration
in a public header file (algorithm.h in this case)
and defining the new type in a private implementation file
(algorithm.c in this case).

I'm sorry about my misunderstandin g of "opaque" data types in my
previous posts. I was not familiar with this concept. It is not my
goal to create "opaque" data types. I am writing application code and
not API code. My intention was to prevent external functions from
modifying my "hidden" (statically declared) data structures. I did not
want to "hide" the members of the structure. I realize this is
primitive compared to your code (which, I admit, I did not
understand). I am just trying to find a better alternative to using
all global variables which our legacy code currently uses. Note, our
project is relatively small at ~10,000 lines of code. Do you think my
method would be an improvement to using all global variables?

[E. Robert Tisdale]

sofeng wrote:

On Apr 11, 5:43 pm, "E. Robert Tisdale" <e...@netwood.n etwrote:

>The C computer programming language supports encapsulation
but *not* data hiding (like the private label in C++).
C programmers have always used "opaque" data types
when they need to "hide" data.
This is accomplished by publishing a type declaration
in a public header file (algorithm.h in this case)
and defining the new type in a private implementation file
(algorithm.c in this case).

I'm sorry about my misunderstandin g of "opaque" data types in my
previous posts. I was not familiar with this concept. It is not my
goal to create "opaque" data types. I am writing application code and
not API code. My intention was to prevent external functions from
modifying my "hidden" (statically declared) data structures. I did not
want to "hide" the members of the structure. I realize this is
primitive compared to your code (which, I admit, I did not
understand). I am just trying to find a better alternative to using
all global variables which our legacy code currently uses. Note, our
project is relatively small at ~10,000 lines of code. Do you think my
method would be an improvement to using all global variables?

No!

You should avoid global variables including static global variables.
Why can't you use global constants?
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