C - Serialization of the floating point numbers (f

Question

How to convert a floating point number into a sequence of bytes so that it can be persisted in a file? Such algorithm must be fast and highly portable. It must allow also the opposite operation, deserialization. It would be nice if only very tiny excess of bits per value (persistent space) is required.

Answer 1

You could always convert to IEEE-754 format in a fixed byte order (either little endian or big endian). For most machines, that would require either nothing at all or a simple byte swap to serialize and deserialize. A machine that doesn't support IEEE-754 natively will need a converter written, but doing that with ldexp and frexp (stanard C library functions)and bit shuffling is not too tough.

Answer 2

Converting to an ascii representation would be the simplest, but if you need to deal with a colossal number of floats, then of course you should go binary. But this can be a tricky issue if you care about portability. Floating point numbers are represented differently in different machines.

If you don't want to use a canned library, then your float-binary serializer/deserializer will simply have to have "a contract" on where each bit lands and what it represents.

Here's a fun website to help with that: link.

Answer 3

Assuming you're using mainstream compilers, floating point values in C and C++ obey the IEEE standard and when written in binary form to a file can be recovered in any other platform, provided that you write and read using the same byte endianess. So my suggestion is: pick an endianess of choice, and before writing or after reading, check if that endianess is the same as in the current platform; if not, just swap the bytes.

Answer 4

fwrite(), fread()? You will likely want binary, and you cannot pack the bytes any tighter unless you want to sacrifice precision which you would do in the program and then fwrite() fread() anyway; float a; double b; a=(float)b; fwrite(&a,1,sizeof(a),fp);

If you are carrying different floating point formats around they may not convert in a straight binary sense, so you may have to pick apart the bits and perform the math, this to the power that plus this, etc. IEEE 754 is a dreadful standard to use but widespread so it would minimize the effort.