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different max_structs – using the same method – polymorphism

October 9, 2012 | 12:46 pm

Hi, to achieve what is hinted in the title would save me a lot of code duplication. So here’s the problem:

All of my externals contain at least these ingredients

typedef struct
{
t_object standart_header;
int key;
}t_specific_struct;

In my case there’s one class/file containing the functions (which need the key to work)
and there are "sub"files which import the header of that topfile.

Now I would like to use the same methods of that topfile for different max_structs
which depend on that key, knowing that all structs will have that key.

I tried using

typedef struct
{
t_object standart_header;
int key;
}t_generic_struct;

in the topfile because I thought it might work having the same structure but didn’t.


October 9, 2012 | 2:56 pm

Hi, sorry for being a bit imprecise.

———–pseudo-code——————–
//specific part

#import "test_super.h"
int main (int argc, const char * argv[])
{

class_addmethod(c, (method)test_method, "test", 0);
}

// I’d like to avoid this and use "test_method_super" directly
void test_method(t_specific_struct *x)
{
test_method_super(x->key);
}

—————————————————
//generic part – the test_super.c file – how I want it to work

void test_method_super(t_generic_struct * x)
{
do s.th with the key of x; //not possible at the moment
}
————————————————–
If a method interface allows different types as parameters, isn’t that (parametric )polym.?


October 9, 2012 | 6:02 pm

Hi,

this is one of the reasons why I develop my externals in C++ instead of C. Just search the net for ‘object oriented programming’. If in C++, you should check the part where they talk about ‘virtual functions’.

HTH,
Ádám


October 10, 2012 | 10:53 am

Hi,
I got it working with something like Nicolas proposed. Thanks a lot!

This is how:

I made a struct that contains t_object and the key

typedef struct _ob {
t_object o;
int key;
} t_things_in_common;

Using t_ob as the generic type directly didn’t work. All values received were 0.

But making another struct

typedef struct
{
t_things_in_common ob;
}t_generic;

and then using this type in the super method works!

void test_method_super(t_generic * x)
{
do s.th with the key of x; //works now
}

Every object that contains the t_things_in_common struct in first place can use functions
which have t_generic as a parameter type.

typedef struct
{
t_things_in_common
…more ingredients;
}t_specific;

Again thanks for helping out, also for the advice having a look at c++.
Greetings, Alex


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