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Does VC++ allow triple pointers?

Started by blueshogun96 Aug 23, 2011 at 10:06 AM 9 replies 4.3k views

Original Post

Aug 23, 2011 at 10:06 AM

Atm, I'm porting a project (libemu: http://libemu.carnivore.it/) from GCC to Visual Studio.net (C/C++) and so far, I'm a bit confused on the best way to handle this scenario. In the GCC port, there's a pointer allocation using a triple pointer (which I didn't think was possible) allocated by using malloc() for use as a double array of pointers. So, the pointer being allocated is of a void*** type which is allocated like this:

void*** em::pagetable = malloc((1 << (32 - PAGE_BITS - PAGESET_BITS)) * sizeof(void *));

And commonly used like so:

em->pagetable[PAGESET(addr)] = (void**)malloc(PAGESET_SIZE * sizeof(void *));

...

em->pagetable[PAGESET(addr)][PAGE(addr)] = malloc(PAGE_SIZE);

I feel kinda dumb for not knowing the answer to this myself, but I'm trying to get this fixed with minimal hassle. Should I try using new[][][] instead? Or use a different variable type? Thanks.

rip-off

Aug 23, 2011 at 10:30 AM

Try it out...


 #include <iostream>
 
 int main()
 {
 int a = 42;
 int *b = &a
 int **c = &b
 int ***d = &c
 int ****e = &d
 int *****f = &e
 int ******g = &f
 int *******h = &g
 int ********i = &h
 int *********j = &i
 int **********k = &j
 int ***********l = &k
 int ************m = &l
 int *************n = &m
 int **************o = &n
 int ***************p = &o
 
 std::cout << a << ' ' << ***************p << '\n';
 }

There is nothing particularly special about a double pointer, or a triple pointer. Higher orders get rarer though. The head of a linked list of size N can be though of N level pointer to the tail.

Antheus

Aug 23, 2011 at 10:48 AM

Atm, I'm porting a project (libemu: http://libemu.carnivore.it/) from GCC to Visual Studio.net (C/C++) and so far, I'm a bit confused on the best way to handle this scenario. In the GCC port, there's a pointer allocation using a triple pointer (which I didn't think was possible) allocated by using malloc() for use as a double array of pointers. So, the pointer being allocated is of a void*** type which is allocated like this:

void*** em::pagetable = malloc((1 << (32 - PAGE_BITS - PAGESET_BITS)) * sizeof(void *));

And commonly used like so:

em->pagetable[PAGESET(addr)] = (void**)malloc(PAGESET_SIZE * sizeof(void *));

...

em->pagetable[PAGESET(addr)][PAGE(addr)] = malloc(PAGE_SIZE);

Dear god almighty...

I feel kinda dumb for not knowing the answer to this myself, but I'm trying to get this fixed with minimal hassle. Should I try using new[][][] instead? Or use a different variable type? Thanks.
[/quote]
The above does something else.

Try with typedefs:typedef void * FirstPtr; typedef FirstPtr * SecondPtr; SecondPtr * em::pagetable = malloc((1 << (32 - PAGE_BITS - PAGESET_BITS)) * sizeof(void *));

Or, it allocates an array of SecondPtr types. Similar to:SecondPtr sp[(1 << (32 - PAGE_BITS - PAGESET_BITS))];

It does not allocate a 3D array. Just a simple array that contains pointers to (void *).

Also, malloc works just fine in visual studio, why change it?

DarkRadeon

Aug 23, 2011 at 12:26 PM

if you wanna know non-standard behaviors of VC++ compiler you can read this on MSDN library: http://msdn.microsoft.com/en-us/library/x84h5b78.aspx

NightCreature83

Aug 23, 2011 at 9:36 PM

Atm, I'm porting a project (libemu: http://libemu.carnivore.it/) from GCC to Visual Studio.net (C/C++) and so far, I'm a bit confused on the best way to handle this scenario. In the GCC port, there's a pointer allocation using a triple pointer (which I didn't think was possible) allocated by using malloc() for use as a double array of pointers. So, the pointer being allocated is of a void*** type which is allocated like this:

void*** em::pagetable = malloc((1 << (32 - PAGE_BITS - PAGESET_BITS)) * sizeof(void *));

And commonly used like so:

em->pagetable[PAGESET(addr)] = (void**)malloc(PAGESET_SIZE * sizeof(void *));

...

em->pagetable[PAGESET(addr)][PAGE(addr)] = malloc(PAGE_SIZE);

I feel kinda dumb for not knowing the answer to this myself, but I'm trying to get this fixed with minimal hassle. Should I try using new[][][] instead? Or use a different variable type? Thanks.

Don't ever mix new[], delete[] with malloc and free that will lead to undefined behaviour. That tripple pointer stuff makes your eyes bleed though, use some typedefs which could clear up stuff, void* are generally a bad practice in C++. It also smells of a thoughtless port of C code to C++.

blueshogun96

Aug 23, 2011 at 9:55 PM

Thanks for the input guys. It looks like I fixed it (so far), at least I hope I did. So it looks like it's time to press on. Thanks again.

dz32

Oct 4, 2011 at 12:22 AM

here is a VS 2008 port of libemu minus graphing and getpc sections

https://github.com/dzzie/VS_LIBEMU

Oberon_Command

Oct 4, 2011 at 1:05 AM

I actually put this into VC++ and compiled it. It cmpiled just fine.


 
 
 int main(int argc, char * argv[])
 {
 int ****************************************************************************************************************************************************************************************************************************************************************a = NULL;
 
 return 0;
 }