I want to write signed integer values into a file in a platform independent way.
If they were unsigned, I would just convert them from host byte order to LE (or BE) with the endian(3) family of functions.
I’m not sure how to deal with signed integers though. If I cast them to unsigned values, I loose the sign, since the C standard does not guarantee that
(int) ((unsigned) -1)) == -1
The other option would be to I cast a pointer to the value (i.e., reinterpret the byte sequence as unsigned), but it I’m not convinced that converting endianness after that is going to give anything sensible.
What is the proper way for platform independent signed integer storage?
Update:
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I know that in practice, almost all architectures use two-complement representation, so that I can losslessly convert between signed and unsigned integers. However, this is question is meant to be more theoretical.
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Just rolling out my own integer representation (be that storing the decimal letters as ascii characters, or separately storing the sign bit) is of course a solution. However, I’m interested if there is a way that works without completely abandoning the native binary representation.
A platform-independent way? If you truly want this, you should consider writing it as text rather than binary (and taking into account that even that is not fully platform-independent since you may want to move it from an ASCII to an EBCDIC platform).
It all depends on how platform-independent you need it to be. C allows for three different signed encodings: two’s complement, one’s complement and sign/magnitude. But, by far, most machines will use the first one.
Work out first what you actually mean by that term. If you mean you only want to handle two’s complement, then casting it to an unsigned is fine.