Re: Sizes and types for network programming

James Kanze <>
Thu, 16 Sep 2010 02:26:56 -0700 (PDT)
On Sep 15, 8:43 pm, Joshua Maurice <> wrote:

On Sep 14, 6:23 pm, Michael Hull <> wrote:

I have a question, and I hope its not obvious!

As I understand it, C++does not define the number of bits in a byte,
this is architecture independant. The thing we always know are that
sizeof(char) == 1. The sizees of int, long, etc will be architecture
dependant, ie the number of bits in an int on a 32bit machine may be
different to that on a 64bit machine.

I'm not sure exactly what you are saying, so let me make sure it's
clear. sizeof(char) == 1, aka the size of a char is exactly one C++
byte. A C++ byte is not the same thing as a byte in other contexts.

No. C++ requires that a byte be at least 8 bits: historically,
6 and 7 bit bytes were common. (The reason Fortran uses such
a small character set, and doesn't distinguish case, is that it
was first developed on a machine with 6 bit bytes.) Also, C++
requires that an integral number of bytes occupy all of the bits
in any integral type: a PDP-10 traditionally used 5 seven bit
bytes in a 36 bit word (but the size of a byte was programmable,
so 4 nine bit bytes would work for C/C++).

In other contexts, generally a byte is an octet, aka 8 bits.

This is the most frequent situation today. It wasn't in the
past, and the first use of byte refered to six bit bytes.

There's still one platform today where a byte is 9 bits. And
I think some of the embedded processors punt, and make a byte 32
bits (and sizeof(int) 1); this doesn't correspond to the
classical definition, however, which requires that a byte be
smaller than a word.

According to the C++ standard, and some exotic hardware
perhaps, a C++ byte may be 8 bits, 9 bits, 64 bits, etc. Thus,
the effective size of char is also implementation dependent.
Ex: you can't serialize a 64 bit char to a data stream, then
deserialize those 64 bits of information into an 8 bit char on
a regular desktop.

Sure you can (and people do). It just requires some special

James Kanze

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