Accessing child variables through higher level structures

Question

If I have these structures:

typedef struct { int x; } foo;
typedef struct { foo f; } bar;

Normally you would access x through

Answer 1

Since the C standard guarantees that there isn't padding before the first member of a struct, there isn't padding before the foo in bar, and there isn't padding before the x in foo. So, a raw memory access to the start of bar will access bar::foo::x.

You could do something like this:

#include 
#include 

typedef struct _foo
{
    int x;
} foo;

typedef struct _bar
{
    foo f;
} bar;

int main()
{
    bar b;
    int val = 10;

    // Setting the value:
    memcpy(&b, &val, sizeof(int));
    printf("%d\n", b.f.x);

    b.f.x = 100;


    // Reading the value:
    memcpy(&val, &b, sizeof(int));
    printf("%d\n", val);
    return 0;
}

As others have noted, C++ offers a more elegant way of doing this through inheritance.