c - Detecting Endianess -

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c - Detecting Endianess -

i'm trying create c source code handles i/o whatever endianess of target system.

i've selected "little endian" i/o convention, means that, big endian cpu, need convert info while writing or reading.

conversion not issue. problem face observe endianess, preferably @ compile time (since cpu not alter endianess in middle of execution...).

up now, i've been using :

#if __byte_order__ == __order_little_endian__ ... #else ... #endif

it's documented gcc pre-defined macro, , visual seems understand too.

however, i've received study check fails big_endian systems (powerpc).

so, i'm looking foolproof solution, ensures endianess correctly detected, whatever compiler , target system. well, of them @ least...

[edit] : of solutions proposed rely on "run-time tests". these tests may evaluated compilers during compilation, , hence cost no real runtime performance.

however, branching kind of << if (0) { ... } else { ... } >> not enough. in current code implementation, variable , functions declaration depend on big_endian detection. these cannot changed if statement.

well, obviously, there fall plan, rewrite code...

i prefer avoid that, but, well, looks diminishing hope...

[edit 2] : have tested "run-time tests", modifying code. although job correctly, these tests impact performance.

i expecting that, since tests have predictable output, compiler eliminate bad branches. unfortunately, doesn't work time. msvc compiler, , successful in eliminating bad branches, gcc has mixed results, depending on versions, kind of tests, , greater impact on 64 bits on 32 bits.

it's strange. , means run-time tests cannot ensured dealt compiler.

instead of looking compile-time check, why not utilize big-endian order (which considered "network order" many) , utilize htons/htonl/ntohs/ntohl functions provided unix-systems , windows. they're defined job you're trying do. why reinvent wheel?

c preprocessor endianness compile-time

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