What is the use of structure padding in C?

Question

What is structure padding and how it is used at processor level?

Answer 1

Padding is adding extra bits at the end, so that the structure completes the word boundary. Padding is done to do memory alignment. Using
-> #pragma ,
->__attrubute__((_packed_)) ,the strucutre padding can be avoided.
For Example:
P (Padding): (1 bit) Used to indicate if there are extra padding bytes at the end of the RTP packet. A padding might be used to fill up a block of certain size, for example as required by an encryption algorithm. The last byte of the padding contains the number of how many padding bytes were added (including itself)

Answer 2

Some architectures will perform better if only aligned accesses are made, so putting 32-bit objects on 32-bit boundaries, and 64-bit objects on 64-bit boundaries can improve the speed of your application.

Some architectures are completely incapable of making unaligned accesses, and on those architectures not padding can be a real disaster.