obj function hello()

[gert]

#include <stdio.h>

obj function hello(){
struct obj = { char *data = 'hello'}
obj.add = obj_add(obj);
return obj;
}

void function obj_add(obj){
obj function add(value){
obj.data += value;
return obj;
}
}

void main(){
test = hello();
test.add('world ');
printf(test.dat a);
}

I don't know much c and i was hoping the code above was pointing out
what i am trying to do ?

[Ian Collins]

gert wrote:

#include <stdio.h>

obj function hello(){
struct obj = { char *data = 'hello'}
obj.add = obj_add(obj);
return obj;
}

void function obj_add(obj){
obj function add(value){
obj.data += value;
return obj;
}
}

void main(){
test = hello();
test.add('world ');
printf(test.dat a);
}

I don't know much c and i was hoping the code above was pointing out
what i am trying to do ?

You are attempting to write something almost, but not entirely, unlike
C. It is more like JavaScript.

You can't bind functions (or anything else) to structs at runtime in C.

--
Ian Collins.

[gert]

i started from python actually. I was trying to figure out how to make
a struct that has data and functions defined in the struct it self ?

[Ian Collins]

gert wrote:

i started from python actually. I was trying to figure out how to make
a struct that has data and functions defined in the struct it self ?

Please keep the context you are replying to.

You can't have functions in structs in C. What yo can have is function
pointers:

struct Obj {
int someInt;
int (*someFn)(void) ;
};

But you have to assign a function address to the pointer for each
instance of Obj.

--
Ian Collins.

[gert]

On Feb 9, 1:30 am, Ian Collins <[e-mail] mwrote:

You can't have functions in structs in C. What yo can have is function
pointers:

struct Obj {
int someInt;
int (*someFn)(void) ;

};

But you have to assign a function address to the pointer for each
instance of Obj.

So this means i have to do something like this then ?

#include <stdio.h>

struct obj {
char *data = ''
int (*add)(void);
}

function add(char *value){
obj.data += value;
}

obj function hello(){
obj.data = 'hello';
return obj;
}

void main(){
test = hello();
test.add('world ');
printf(test.dat a);
}

[Ian Collins]

gert wrote:

On Feb 9, 1:30 am, Ian Collins <[e-mail] mwrote:

>>You can't have functions in structs in C. What yo can have is function
pointers:

struct Obj {
int someInt;
int (*someFn)(void) ;

};

But you have to assign a function address to the pointer for each
instance of Obj.

So this means i have to do something like this then ?

#include <stdio.h>

struct obj {
char *data = ''
int (*add)(void);
}

No, you are still assuming C is an OO language. In C you have to be
explicit:

#include <stdio.h>
#include <stdlib.h>

typedef struct Obj {
int value;
int (*add)(struct Obj*,int);
} Obj;

int add( Obj* obj, int val ) {
obj->value += val;
return obj->value;
}

int main(void) {
Obj* obj = malloc( sizeof obj );

obj->value = 0;
obj->add = add;

obj->add( obj, 42 );

printf( "%d\n", obj->value );

return 0;
}

--
Ian Collins.

[Ian Collins]

Ian Collins wrote:

int main(void) {
Obj* obj = malloc( sizeof obj );

Oops, malloc( sizeof *obj );
--
Ian Collins.

[Nick Keighley]

On 9 Feb, 00:43, "gert" <gert.cuyk...@g mail.comwrote:

On Feb 9, 1:30 am, Ian Collins <[e-mail] mwrote:

<snip>

So this means i have to do something like this then ?

you can't write programs in *any* language by guessing the syntax.
Get a good book (eg. http://cm.bell-labs.com/cm/cs/cbook/index.html).

#include <stdio.h>

struct obj {
char *data = ''

string (aka char*) constancts are delimited by " (double quote)
not ' (single quote)

int (*add)(void);

}

function add(char *value){

C has no keyword "function". A function must return a value.

obj.data += value;

obj hasn't been defined. Is obj a type or a variable?

>
}

obj function hello(){
obj.data = 'hello';
return obj;

}

void main(){

int main(void)

test = hello();

test is not defined. This is the wrong syntax for function pointer
assignment.
Or is it a struct assignment? C is strongly typed. You need to decide
on the
type for everything.

test.add('world ');
printf(test.dat a);
}

but the basic problem is you are trying to learn C by guessing.
--
Nick Keighley

[Christopher Benson-Manica]

gert <ge**********@g mail.comwrote:

So this means i have to do something like this then ?
(snip not-C)

No, not really. I've taken the liberty of translating your pseudo-C
into a real C program - which is syntactically correct but *will* fail
(produce undefined behavior) at run time. After considering the vast
differences between your conception of C and what C is, I suggest you
take Mr. Tobin's advice and pick up a C textbook before trying
anything else.

#include <stdio.h>
#include <string.h>

struct obj {
char *data;
void (*add)(struct obj *,char *);
};

void add(struct obj *o, char *value){
strcat(o->data, value); /* assume o->data is large enough */
}

struct obj *hello(struct obj *o){
o->data="hello" ;
return o;
}

int main(void){
struct obj test;
hello( &test );

test.add=add;
test.add(&test, "world"); /* Syntatically correct but WRONG */
printf("%s\n",t est.data);
return 0;
}

--
C. Benson Manica | I *should* know what I'm talking about - if I
cbmanica(at)gma il.com | don't, I need to know. Flames welcome.

[gert]

On Feb 9, 2:41 am, Ian Collins <[e-mail] mwrote:

No, you are still assuming C is an OO language. In C you have to be
explicit:

#include <stdio.h>
#include <stdlib.h>

typedef struct Obj {
int value;
int (*add)(struct Obj*,int);

} Obj;

int add( Obj* obj, int val ) {
obj->value += val;
return obj->value;

}

int main(void) {
Obj* obj = malloc( sizeof obj );

obj->value = 0;
obj->add = add;

obj->add( obj, 42 );

printf( "%d\n", obj->value );

return 0;

}

Thanks this is exactly what i was guessing for :) I always start from
this example to learn a language. It defines for me a basic learning
path. So if something doesn't work i have this example to figure out
why a other example doesnt work. I can read about pointers, structs
and functions but that doesnt mean i understand it.

One last sub question, is this a good way to make programs in C by
defining a struct and assign function pointers to it to make it look
like a oo. Or are there other recommended methods to make a program.