Structs are just abstractions (proof)

[Govind]

Proof that structs are just abstractions of contiguous memory:

#include <stdlib.h>
#include <stdio.h>
typedef struct __s1
{
	int a;
	int b;
} s1;

int main()
{
	long f = 0;
	s1 st;
	st.a = 7;
	st.b = 4;
	memcpy(&f, &st, 4);
	printf("%d\n", f);
	return 0;
}

f = 7.

 

Careful, the padding in a struct is based on the architecture's data alignment.

 

[Govind]

Would there be padding before the first variable? Besides, no type other than int is used.

 

Would there be padding before the first variable? Besides, no type other than int is used.

Not usually, but strictly speaking it's up to the compiler.

Examples:
http://msdn.microsoft.com/en-us/library/71kf49f1(v=vs.80).aspx

 

[Blondi]

Yikes SMR, I wouldn't do that except for experimental/demonstration purposes: as was correctly noted above, there is usually no padding before the first variable in a struct, but what if you were on an architecture where an int is 2 bytes, not 4? The result would be (7 << 2 | 4), whatever that works out to.