How to Convert 64-Bit Integers Between Big and Little Endian Using htobe64() and be64toh()?

64-Bit Integer Conversion: Leveraging htobe64() and be64toh()

The ntohl() function in C is primarily utilized for 32-bit values, leaving developers seeking a solution for converting 64-bit integers. To address this need, we explore the use of htobe64() and be64toh() for effectively performing big endian to little endian conversion.

The availability of htobe64() and be64toh() varies across platforms. Linux (glibc >= 2.9), OpenBSD, FreeBSD, and NetBSD provide direct access to these functions. However, to ensure compatibility across different OSes, the following preprocessor code can be employed:

<code class="cpp">#if defined(__linux__)
#  include <endian.h>
#elif defined(__FreeBSD__) || defined(__NetBSD__)
#  include <sys/endian.h>
#elif defined(__OpenBSD__)
#  include <sys/types.h>
#  define be16toh(x) betoh16(x)
#  define be32toh(x) betoh32(x)
#  define be64toh(x) betoh64(x)
#endif</code>

This code provides a unified interface across platforms, allowing developers to use the functions with the desired functionality. The usage pattern is straightforward:

<code class="cpp">  uint64_t host_int = 123;
  uint64_t big_endian;

  big_endian = htobe64( host_int );
  host_int = be64toh( big_endian );</code>

By leveraging htobe64() and be64toh(), you gain a consistent and efficient method for converting 64-bit integers between big endian and little endian formats, regardless of the target platform.

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