(C++) Get the byte-values from an unsigned int32

[phiber4591]

Hi there,

I'm trying to "convert" an unsigned int32 to an array of bytes (with a length of 4, of course). Everything i tried up to now didn't work out, so I would really appreciate any help or tip ;-)

My idea is that an uint32 has a length of 4 bytes, and thus it should be possible to take these bytes on their own and do something with them.

Short example:
uint32 contains the (dec) value 439041101, which is in hex 1A2B3C4D.

All I want is an array of 4 char's or bytes with the values:
ret[0]: 1A
ret[1]: 2B
ret[2]: 3C
ret[3]: 4F
(hex-value [and not a string])


Many thanks in advance,

phiber

[Banfa]

Here's 2 methods:

1. Take a pointer to your integer and cast it to a pointer to unsigned char, not portable but does work on most systems today.

2. Create a union of 1 int and an array of 4 bytes, assign you int to an instance of the union and then read out the byte array.

[JosAH]

@Banfa
Both these methods fail on a little endian machine but the htonl macro can be of help then.

kind regards,

Jos

[Banfa]

@JosAH
I think what you mean is both those methods have to take the endian of the machine into account when copying the data out into your array and are therefore non-portable.

On the other hand htonl is part of a third party library that is not available on all platforms and there for also non-portable.

The portable method is to use the bitwise right shift and and operators to extract the byte values.

:D

[JosAH]

@Banfa
IMHO that borders to paranoia; if a platform even smells like POSIX it has those functions/macros available.

kind regards,

Jos

[Banfa]

True but 90% - 100% of the reasonable number of platforms I have worked on have not smelt like POSIX at all.