Endianness

* Memory Allocation Rule
In general, the memory is allocated for data starting from low address in the stack(grow from high address to low address) and the heap.

* Endianness
Most modern computer processors agree on bit ordering "inside" individual bytes (this was not always the case). This means that any single-byte value will be read the same on almost any computer one may send it to.

Integers are usually stored as sequences of bytes, so that the encoded value can be obtained by simple concatenation. The two most common of them are:
- increasing numeric significance with increasing memory addresses, known as little-endian, and
- its opposite, called big-endian.
The bit order of register in CPU is fixed for both endians and hardware would take charge of conversion between register and memory.

* Endianness in Networking
Data is transfered generally byte by byte from low address (char *buffer). Networks generally use big-endian order for BYTE transmission (maybe not in memory), and thus it is called network order when sending information over a network in a common format. Some routines are provided generally for these conversions between network and host.

* Bit-Level Endianness
Bit endianness is used to refer to the transmission order of bits over a serial medium. Most often that order is transparently managed by the hardware and is the bit-level analogue of little-endian (low-bit first), although protocols exist which require the opposite ordering (e.g. I2C). In networking, the decision about the order of transmission of bits is made in the very bottom of the data link layer of the OSI model.

* Bit-Shift and Endianness
Bit-shift has nothing with endianness. The results of these operations are defined by std and implemented by compiler.
Reference: Endianness in Wikipedia