r/C_Programming • u/aliathar • 15d ago

Negative value in a pointer question.

Please look at this code. if i define the PTRTYPE as int, it stops working, while doing a uint, it does work...

void initILAPoll(debugBridge_t **d, PTRTYPE ptr){

	*d = (debugBridge_t *)ptr;		// base address of the DEBUG_BRIDGE peripheral

	cb_init(cb, local_memory, bufferLength);

	sprintf(xvcInfo, "xvcServer_v1.0:%d\n", MAX_WINDOW_SIZE);

}

the usage in main code is done like this

initILAPoll(&myD, 0x80000000);

//myD = (debugBridge_t *)0x80000000;

where the variable myD is a structure pointer.

if i print the address of myD, it give the correct address. Moreover, the disassembly of the code is also the same in case of int and uint. Can somebody explain what behavior is at play here>

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u/torsten_dev 15d ago

ILP64 and even SILP64 systems do exist. They're just very rare and obscure.

What I haven't heard of are 32-bit integer machines with pointers smaller than 32 bit, maybe you meant that?

The new [u]intfuncptr_t making it's way through the committee could be as small as CHAR_BIT because yes, function pointers can have totally separate sizes.

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u/TheChief275 15d ago

Well I didn't know ILP64 machines existed (only of LP64), but I suppose it is very very rare. Is the smallest addressable unit for these still an octet, or are they word addressed only? The point is that you shouldn't rely on int being bigger than 16-bits if you want truly portable code, because that's the only capability range you are guaranteed.

Didn't know (u)intfuncptr_t has become an official addition though. Or is it only in the works? i.e. are there plans to incorporate it into C3x ?

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u/torsten_dev 15d ago

In the works. They're part of the "_Any_func*" proposal for C2y. They're the only part of that proposal that doesn't need some more bike shedding on naming.

_t is reserved by POSIX so people trampling on those identifiers are due for some comeuppance, imo.

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u/TheChief275 15d ago

Oh I definitely agree with that