be32toh

be32toh is a macro or inline function used in C and C++ to convert a 32-bit unsigned integer from big-endian byte order to the host's native byte order. The name conveys its purpose: be32toh means “big-endian 32 to host.” It is commonly used when reading binary data formats or network protocols that specify 32-bit fields in big-endian representation.

The behavior of be32toh depends on the host's endianness. On a big-endian system, be32toh(x) typically returns x unchanged. On a little-endian system, it swaps the byte order of the 32-bit value so that the value is interpreted correctly in the host’s native representation. For example, be32toh(0x01020304) would yield 0x04030201 on a little-endian host.

Be32toh is typically defined in system headers such as endian.h or sys/endian.h, with variations across Unix-like platforms. Its availability and exact naming can differ; some systems may provide be32toh alongside be16toh and be64toh, while others expose similar facilities under different headers or via alternative functions.

The macro is closely related to htobe32, which performs the inverse operation (host to big-endian). In network programming, be32toh is conceptually similar to ntohl, but be32toh emphasizes conversion from a big-endian representation regardless of whether the data originated from a network source.

Usage is common when parsing binary formats or files that specify big-endian 32-bit fields, ensuring that subsequent arithmetic and comparisons use the host’s native byte order. If platform support is absent, developers may fall back to explicit byte-swapping routines or portable alternatives. See also be16toh, be64toh, htobe32, and ntohl.