struct pointer to struct pointer..??

[paret]

I am experiencing problems with a program that involves alot of structures and pointers, i think i have narrowed my problem down to an issue with ether assigning or referencing struct memebers...

if I have:

struct ONE{

   struct TWO* two_pointer;

};

struct TWO{

   int value;
};

if im in a situation where i have to fill the memeber value of struct TWO with x, but i can only directly acces struct ONE, is this not the proper procedure..?

struct ONE* one_p=(struct ONE*)malloc(sizeof(struct ONE));
struct TWO* one_p->two_pointer=(struct TWO*)malloc(sizeof(struct TWO));

one_p->two_p->value=x;

[quzah]

You're still compiling as C++ if you have to typecast malloc to stifle warnings.

#include<stdio.h>
#include<stdlib.h>
int main( void )
{
    struct foo
    {
        int x;
    };
    struct bar
    {
        struct foo *y;
    } *baz;

    if( (baz = malloc( sizeof *baz )) )
    {
        if( (baz->y = malloc( sizeof *(baz->y) )) )
        {
            baz->y->x = 5;
            printf( "%d\n", baz->y->x );
            free( baz->y );
        }
        free( baz );
    }

    return 0;
}

I find it always best to make a small compilable example.


Quzah.

[paret]

Day #8 now of trying to figure this out...im debating on giving up programming for good.....ive tried to rewrite this program 101 ways now,including your solution quzah and im still in the same place i was last week...when i tried to write it the memory allcoation part liek you told me to

baz = malloc( sizeof *baz ))

it tells me that i cant cast from void* to "bar"*
also what im noticing is that i have split everything up into different modules

construct(pointer)...allocates memory
initialize(pointer)...fills with values
use(pointer)....use it
destruct(pointer)...free memory

whats weird is that it appears as if the program is jsut not calling or not entering construct_pointer()..ill place breakpoints at lines of code inside the construct() function,but when i start the debugger, the breakpoints are removed and replaced with warnings saying "The breakpoint will not be hit. No Excecutable code is associated with this line"...anyone know why thats happening?

[paret]

heres the exact flow control of my program (simplified)..hopefully someone can see what i am doing wrong..

struct Gemstone* gem;
main(){

construct_gem(gem);
initialize_gem(gem);
use_gem(gem);
destruct(gem);
}

construct_gem(struct Gemstone* gem_p){

	gem_p=(struct Gemstone*)malloc(sizeof(struct Gemstone));
	gem_p->position=(struct Point*)malloc(sizeof(struct Point));
	gem_p->position->x=0;
	gem_p->position->y=0;
	gem_p->size=0.5;
	gem_p->value=10;

      //none of this code seems to be excecuted

}
initialize_gem(struct Gemston* gem_p){

   gem_p->postion->x=-0.77
   gem_p->position->y=0.93
  //more code that is irrelevant

}

use_gem(struct Gemstone* gem_p){
}
destruct_gem(struct Gemstone* gem_p(struct Gemstone* gem_p)

[itCbitC]

Yep! it is the proper procedure with minor changes to the line shown below, hope that will fix your issue:

struct TWO* one_p->two_pointer=(struct TWO*)malloc(sizeof(struct TWO));

should be written as

one_p->two_pointer=(struct TWO*)malloc(sizeof(struct TWO));

[paret]

that actualy is how i worte it in the code, when i wrote it above, i accidently put in the extrat struct TWO*...and if that is the proper procedure, then cleary the problem is somewhere else..

[quzah]

baz = malloc( sizeof *baz ))

it tells me that i cant cast from void* to "bar"*

You either aren't including the right header, or you are compiling as C++.

construct(pointer)...allocates memory

Won't work unless you're assigning a return value, or are using a pointer to a pointer.

void foo( type *bar )
{
    bar = malloc( ... ); /* no */
}

void foo( type **bar )
{
    *bar = malloc( ... ); /* yes */
}

type *foo( ... )
{
    type *p;
    p = malloc( ... );
    ...
    return p; /* yes */
}

Quzah.

[paret]

your rightt!....that makes sense...thanks man!!