Memory alignment cases.

align.c

#include <stdio.h>

struct P1 { int i; char c; long j; char d; };
struct P2 { long j; char c; char d; int i; };
struct P3 { short w[3]; char c[3]; };
struct P4 { short w[3]; char *c[3]; };
struct P5 { struct P1 a[2]; struct P2 *p; };

int main()
{
    struct P1 p1;
    struct P2 p2;
    struct P3 p3;
    struct P4 p4;
    struct P5 p5;

    printf("struct P1 { int i; char c; long j; char d; };\n");
    printf("total=%lu, offsets: %ld %ld %ld %ld\n\n", sizeof(p1), (unsigned char *)&p1.i - (unsigned char *)&p1, (unsigned char *)&p1.c - (unsigned char *)&p1, (unsigned char *)&p1.j - (unsigned char *)&p1, (unsigned char *)&p1.d - (unsigned char *)&p1);

    printf("struct P2 { long j; char c; char d; int i; };\n");
    printf("total=%lu, offsets: %ld %ld %ld %ld\n\n", sizeof(p2), (unsigned char *)&p2.j - (unsigned char *)&p2, (unsigned char *)&p2.c - (unsigned char *)&p2, (unsigned char *)&p2.d - (unsigned char *)&p2, (unsigned char *)&p2.i - (unsigned char *)&p2);

    printf("struct P3 { short w[3]; char c[3] };\n");
    printf("total=%lu, offsets: %ld %ld\n\n", sizeof(p3), (unsigned char *)&p3.w - (unsigned char *)&p3, (unsigned char *)&p3.c - (unsigned char *)&p3);

    printf("struct P4 { short w[3]; char *c[3]; };\n");
    printf("total=%lu, offsets: %ld %ld\n\n", sizeof(p4), (unsigned char *)&p4.w - (unsigned char *)&p4, (unsigned char *)&p4.c - (unsigned char *)&p4);

    printf("struct P5 { struct P1 a[2]; struct P2 *p; };\n");
    printf("total=%lu, offsets: %ld %ld\n\n", sizeof(p5), (unsigned char *)&p5.a - (unsigned char *)&p5, (unsigned char *)&p5.p - (unsigned char *)&p5);

    return 0;
}