be16toh

be16toh is a macro or inline function used in C and C++ programs to convert a 16-bit value from big-endian byte order to the host machine’s native byte order. It is the inverse of htobe16 and is commonly grouped with other endian conversion utilities such as be32toh and be64toh. The name reflects its purpose: transforming data stored in big-endian format (often referred to as network byte order) into the host’s endianness.

Availability and portability: On POSIX-like systems, be16toh is typically defined in endian.h or sys/endian.h and is provided alongside related macros like be32toh, be64toh, and their host-to-big-endian counterparts. Implementations generally rely on compile-time checks of the host’s byte order. If the host is big-endian, be16toh is typically a no-op; if little-endian, it performs a 16-bit byte swap.

Usage: be16toh is used when reading binary data that is specified as big-endian, ensuring that the value is interpreted correctly on the host. For example, when parsing a protocol field or a binary file format that stores values in network byte order, one would convert each 16-bit field to host order before further processing.

Example:

#include <endian.h>

uint16_t net = 0x1234; // big-endian data

uint16_t host = be16toh(net);

Implementation notes: Implementations may use conditional compilation to select a fast byte-swap intrinsic or a portable shift-based swap. On big-endian hosts, be16toh may simply return the input value; on little-endian hosts, it swaps the two bytes.

See also: htobe16, be32toh, be64toh, be16toh’s sibling functions provide host-to-big-endian conversions. If a platform lacks the macro, manual byte-swapping or platform-specific equivalents can be used.