#include struct sss{ int :0; int i2:24; int i3:24; }; static union u{ struct sss sss; unsigned char a[sizeof (struct sss)]; } u; int main (void) { int i; for (i = 0; i < sizeof (struct sss); i++) u.a[i] = 0; u.sss.i2 = 16777215.0; for (i = 0; i < sizeof (struct sss); i++) printf ("%x ", u.a[i]); printf ("\n"); u.sss.i3 = 16777215.0; for (i = 0; i < sizeof (struct sss); i++) printf ("%x ", u.a[i]); printf ("\n"); return 0; }