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"p" is now pointing atCode:int *p = new int;
p = 0x123;
(the 123*2 th byte of the memory of my program) or
(the 123*2 th byte of the whole memory) ??
/*====================================*/
and if i want to change another process's memory ,
how to do ? ( MFC or API )
/*====================================*/
THX.
int *p = new int;
p = 0x123;
That is incorrect. There is no need to allocate that integer. Try:
int *p = 0x123;
or
int *p = (int*)0x123;
And I believe the address would be relative to the program's workspace. Anyway, protected-mode OS's like Windows won't let you enter an address space outside of the process you're in (in theory, at least. I once traversed my entire hard-drive with a far pointer. The catch was, I couldn't dereference the pointer without a seg-fault, but I could index through it with impunity(But then, how useful is that?). ).
Each running process is allocated a 4GB virtual address address space.........When you use a pointer in usermode (be it from C++, Pascal,ASM,....whatever) you can access any memory location in this 4GB address space.....but many locations will throw access violations if you try to access them.
It is possible to change other process's memory without shifting into kernelmode.......you can do stuff like forcing a process to load a dll of your making....or you can use WriteProcessMemory.....its not a very nice thing to do normally though
thx twos. ;)
->if the 4GB's is used up , what will happen??Quote:
Originally posted by Fordy
Each running process is allocated a 4GB virtual address address space.........When you use a pointer in usermode (be it from C++, Pascal,ASM,....whatever) you can access any memory location in this 4GB address space.....but many locations will throw access violations if you try to access them.
It is possible to change other process's memory without shifting into kernelmode.......you can do stuff like forcing a process to load a dll of your making....or you can use WriteProcessMemory.....its not a very nice thing to do normally though
->and if there is 4GB for every process, much of the 4GB's memory may be waste, will the OS optimize about this ??
That 4GB is theoretical......you dont use it all.......what is actively running is in RAM......what needs memory, but is not being used is paged to disk......and what is not used simply not committedQuote:
Originally posted by L.O.K.
thx twos. ;)
->if the 4GB's is used up , what will happen??
->and if there is 4GB for every process, much of the 4GB's memory may be waste, will the OS optimize about this ??
ok , got .Quote:
Originally posted by Fordy
That 4GB is theoretical......you dont use it all.......what is actively running is in RAM......what needs memory, but is not being used is paged to disk......and what is not used simply not committed
That 4 GB comes from the fact that a pointer is ususally 4 bytes. At 8 binary bits per byte that's 2^32 different byte locations that you can address in a 4 byte pointer.
That's
4294967296 Bytes
which is 4194304 Kilobytes
which is 4096 Megabytes
which is 4 Gigabytes worth of bytes that you can address.
If you need to address more than 4 Gigabytes of memory and you are limited to a 4 byte pointer, then you have to do a bit of extra work to access those locations.