Question

#define MAX 100

struct bs{
 int ab;
 int ac;
}be;
struct s{
 be b;
 int c;
 int d;
 int e;
}fe;

int a[MAX];
fe f;

Technique 1:

f.b.ab = a;
memset(&a,0,sizeof(a));
f.b.ac = MAX;

Technique 2:

f.b.ab = a;
f.b.ac = MAX;
memset(&a,0,sizeof(a));

Technique 3:

memset(&a,0,sizeof(a));
f.b.ab = a;
f.b.ac = MAX;

which is the best technique to follow and why?

Answer 1

Technique 3:

memset(&a,0,sizeof(a));
f.b.ab = a;
f.b.ac = MAX;

because both a and fb.b.ab will have clear memories with only one memset() call. Any other kind of optimization you might been hoping for is insignificant.