Re: [paho-dev] MQTT-SN and MQTT embedded C client updates

[Frank Pagliughi <fpagliughi@xxxxxxxxxxxxxx>]

On 08/02/2014 06:08 AM, Ian Craggs wrote:
> Packet ids have been changed to "unsigned short", and data buffers to 
> "unsigned char".  Now the data types are also consistent between the 
> MQTT and MQTT-SN libraries, which was another motivation.

Is there a reason why you wouldn't use the C99 sized types (uint16_t, 
int32_t, etc) from <stdint.h>?  Most compilers support them now - even 
for embedded chips - and it reduces the headaches for portability. If a 
particular compiler/platform doesn't have them, it's easy to define them 
for that compiler.

> I'm not expecting any further data type changes unless a good reason 
> appears.  I started using size_t for buffer sizes, but have stuck with 
> ints to reduce dependencies on any headers - just in case some 
> esoteric/old embedded compiler didn't like size_t.

I would suggest trying to make the 'size_t' work. A lot of 
compilers/platforms have different sizes for 'int' and 'size_t'. The 
'int' type is (normally) the native register size whereas 'size_t' is 
supposed to be the addressable memory space. So 'size_t' can be a larger 
type than 'int'. On the GCC x86_64, 'int' is 32-bits whereas 'size_t' is 
64-bits. On some 16-mit microcontrollers, 'int' is 16-bits, whereas 
'size_t' is 32-bits.

So if you use 'int' as an array index you might not be able to express 
the actual length of an MQTT packet on smaller platforms.

Frank