data structures

**kiros88** · 09-16-2009

Code:

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

struct foo
{
    unsigned int a:16;
    unsigned int b:8;
    unsigned int c:4;
} *fooptr = NULL;

int main( void )
{
    if( (fooptr = malloc( sizeof *fooptr )) == NULL )
        printf( "malloc failed, that's bad\n" );
    else
    {
        fooptr->a = 1;
        fooptr->b = 2;
        fooptr->c = 3;
        free( fooptr );
    }
    return 0;
}

In this sorta of example i just wanted to know how to assign a whole number when you split up the int into a b c but if i know the whole unsigned int could i just assign it without
fooptr->a = 1;
fooptr->b = 2;
fooptr->c = 3;

**quzah** · 09-16-2009

You wouldn't. Your structure doesn't allow for that. You are restricting the size of the varaible's allowed values here. Also, you aren't using a union, so it's not an "either or" sort of thing. It's a structure, that typically means it has multiple members.

Quzah.

**kiros88** · 09-16-2009

So theres not shortcut to defining the members all together its just a whole bunch of multiple definitions

**bithub** · 09-16-2009

Is this what you're looking for?

Code:

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

struct foo 
{
    unsigned int a:16;
    unsigned int b:8;
    unsigned int c:8;
};

struct bar 
{
    union
    {   
        struct foo f;
        unsigned int i;
    };  
};

int main(void)
{
    struct bar b1; 

    b1.i = 0x01234567;

    printf("a = %x\n", b1.f.a);
    printf("b = %x\n", b1.f.b);
    printf("c = %x\n", b1.f.c);

    return 0;
}

**kiros88** · 09-17-2009

I figured it out I wanted something like this to define the members in one go

*(unsigned int *)&fooptr = 0x234324;

**quzah** · 09-17-2009

That assumes of course that your structure is packed the way you expect it to be packed...

Quzah.

**nonoob** · 09-18-2009

You should malloc for sizeof foo (the struct) instead of the pointer's size.

**bithub** · 09-18-2009

Originally Posted by nonoob

You should malloc for sizeof foo (the struct) instead of the pointer's size.

He's not using the size of the pointer, he is using the size of the pointer's type. In other words, the way he has it is correct.

**quzah** · 09-18-2009

Actually he isn't using anything. That's my code example from another thread.

Quzah.

Thread: data structures

Thread Tools

Search Thread

Display

data structures

Similar Threads

What's a good generalized data structures book?

i need advice about data structures

Need some help regarding data structures

array of structures, data from file

Array Data Structures