function pointer within a struct? 1

[Flappy]

how would i go about having a function pointer within a struct?

i've gotten this far and it seems to work but the function doesnt seem to be getting called:


struct Page {
char* title;
...
void (*out)(const char*);
}

void out(const char* str) {
printf("%s\n",str);
}

struct Page* pg;
pg->out=out;


pg->out("Hello"

 

[Flappy]

sorry i left this out after the "struct Page* pg" declaration:

pg=(struct Page*)malloc(sizeof(struct Page));

 

[marsd]

Try this example and see if you can pick out any
mistakes in what you are doing. I don't see any quickly.

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

typedef struct {
float *attr;
char name[20];
float *(*fptr)(void);
} MOON;


float *retArr(void);

int main(void) {
MOON *xmoon = malloc(sizeof(MOON));
xmoon->fptr = retArr;

     printf(&quot;Name of moon: &quot;);
           fgets(xmoon->name,20,stdin);
           xmoon->attr = xmoon->fptr();
           printf(&quot;MOON: %s..Size: %f, Magnitude %f, Brightness %f\n&quot;,xmoon->name,xmoon->attr[0],
           xmoon->attr[1],xmoon->attr[2]);
            
return 0;
}


float *retArr(void) {
int i = 0;
float *array = malloc(3 * sizeof(float));
   
   if (array) {
       while (i < 3) {
             array[i] = (float)(1 + rand() % 15);
             i++;
       }
       return array;
   }

return NULL;
}

 

[bluenote]

struct Page {
char* title;
...
void (*out)(const char*);
};

void out(const char* str) {
printf("%s\n",str);
}

struct Page* pg;

//you have forgotten this line (i guess)
pg=(struct Page*)malloc(sizeof(struct Page));

pg->out=out;


pg->out("Hello"
bluenote@clorinda.dnsq.org
(excuse my english)

 

[Flappy]

its ok guys ive managed to get it to work - the actual piece of code that im programming is alot larger and was too big to paste into here....

but while on the subject is it possible for the "out" function to know what struct variable is calling it? as in like OOP

i know that i could just do this:

pg->out(pg,"Hello"

and use the first argument to pass the pointer of the structure but is it possible to know the calling variable or somehow read back or forward within the struct to access other struct members without having to pass the pg variable to the function?

sorry if im getting confusing :/

 

[marsd]

You want an object oriented approach use an OO
language. You can emulate the behavior you want.
Here is an OK example and the site has some tips:

http://www.eventhelix.com/RealtimeMantra/basics/object_oriented_programming_in_c.htm#C Source Code

 

[Flappy]

thanks, thats excatly what im after - i normally program in c++ but the current server im working on at the moment only has gcc

 

[marsd]

You should have the g++ compiler included with your
gcc installation.
If you only had cc that would be another thing
altogether..