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 struct P1 short i; int c; int *j; short *d; ;
 struct P4 char w[16]; char *c[2]; ;
 struct P5 struct P4 a[2]; struct P1 t; ;

I have a couple of question about padding. I have learned that padding is applied by default.

So I think offset of struct P1 should be

i c j d total alignment
---------------------------------------
0 2 8 16 24 8

and for struct P5

a t total alignment
----------------------------
0 64 96 8

since total size of P4 is 32byte.
But the textbook solution is different. I think I am correct.

Solution suggests

i c j d total alignment
---------------------------------------
0 2 6 14 16 8


a t total alignment
----------------------------
0 24 40 8

The exact details of structure padding are implementation defined. However, compilers do tend to place fields at an alignment suitable for their type.

Assuming 8 byte pointers (given that you're on an x86-64 machine) 4 byte int and 2 byte short, you're mostly correct. The c field in P1, being an int, will probably start at a 4 byte offset, but the rest of the fields should be at the same offsets. The size of P5 will also only need to be 88 (64 for 2 P4's and 24 for 1 P1) since only 8 byte alignment would be required as opposed to 16 byte alignment.

Given this code:

printf("sizeof p1 = %zun", sizeof(struct P1));
printf("sizeof p4 = %zun", sizeof(struct P4));
printf("sizeof p5 = %zun", sizeof(struct P5));
printf("P1 offset: %zu, %zu, %zu, %zun",
 offsetof(struct P1, i), offsetof(struct P1, c),
 offsetof(struct P1, j), offsetof(struct P1, d));
printf("P4 offset: %zu, %zun",
 offsetof(struct P4, w), offsetof(struct P4, c));
printf("P5 offset: %zu, %zun",
 offsetof(struct P5, a), offsetof(struct P5, t));

My x86-64 CentOS 7 machine with gcc 4.8.5 outputs:

sizeof p1 = 24
sizeof p4 = 32
sizeof p5 = 88
P1 offset: 0, 4, 8, 16
P4 offset: 0, 16
P5 offset: 0, 64

The book you're using seems to be using 4 byte pointers and assumes either no alignment or packed structures.

For more details, take a look at The Lost Art of Structure Padding.