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.

 

[Sythe]

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.

 

[Sythe]

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.