C++ Language & SafetyLesson 19 of 441 min read7 questions

Endianness

Byte order of multi-byte values; only visible in raw bytes.

Concept core idea Watch out easy to get wrong

Concept

Key concepts

Endianness = the order bytes of a multi-byte value are stored. Little-endian stores least-significant byte first (x86/x64, most ARM); big-endian stores most-significant first.
The value (how we write a number, MSB first) looks like big-endian; little-endian storage is reversed — flip to read it.
Applies to EVERY multi-byte value (int, pointer). A pointer is just an 8-byte integer → stored little-endian too.
Only visible in raw bytes (hex dump, char*, cross-machine data). cout/printf show the actual number, never reversed.
Single bytes (char) are unaffected; network byte order is big-endian (htonl/ntohl).

Code

int x = 500;   // 0x000001F4
memory (little-endian): F4 01 00 00
reverse -> 00 00 01 F4 = 500

Watch out

little vs big endian

Little = least-significant byte at the lowest address (reversed from writing). Big = most-significant first (reads naturally).

stored bytes vs the value

Raw bytes are endian-dependent (reversed on little-endian). The printed value is always normal (MSB-first) — the CPU reorders for you.

cout pointer vs raw bytes

cout << p prints the real address (readable). Walking (char*)&p shows the little-endian bytes (reversed).

7 questions on this lesson. Write your answers from memory, then compare them with the model answers side by side.