run-time cast possible in c++ ?
Author
Hi ppl,
as stated in the topic I''d like to know whether it is possible to change a type at runtime.
I have a pointer pointing to an array. The type of the pointer should vary (char, short, int) depending on certain circumstances so that I can read back a selective amount of data from the array.
Is that possible somehow ?
Lorenz
of course it is. What exactly is your level of knowledge in C++? Casting is a basic staple of understanding it.
Author
Well, since you pointed out my inexperience, could you also provide me with an example ?
Would be very appreciated.
Would be very appreciated.
u32 MyArray[10];
u32 *MyPointer=MyArray;
(u8*)MyPointer=MyArray;
(u16*)MyPointer=MyArray;
i _hope_ this works *G*
u32 *MyPointer=MyArray;
(u8*)MyPointer=MyArray;
(u16*)MyPointer=MyArray;
i _hope_ this works *G*
if you want a generic object type that can hold different kinds of objects, check this out
http://www.cuj.com/documents/s=8034/cuj0010cacciola/cacciola.htm
for general casting, check out
http://www.c-view.org/tech/pattern/cpptips/TypeCheck.html
sorry for ap:ing, i´m in a hurry
later
jens.
http://www.cuj.com/documents/s=8034/cuj0010cacciola/cacciola.htm
for general casting, check out
http://www.c-view.org/tech/pattern/cpptips/TypeCheck.html
sorry for ap:ing, i´m in a hurry
later
jens.
Author
maximAL: nice try 
, thanks anyways.
AP: I'm on it, but didn't find anything yet.
daerid: I'm still waiting
Just to make things clear.
If it is impossible, and that would be my guess, then how do this in a 'really neat' way. I already have solutions but they all suck grace.
Lorenz
[edited by - sprinter_trueno on May 29, 2003 2:58:06 PM]
, thanks anyways.AP: I'm on it, but didn't find anything yet.
daerid: I'm still waiting
Just to make things clear.
char Array[4];void* pArray = (void*)Array;// Somewhere elseif(...){// Change the type of the pointer somehow to int*// ...}else if(...){// Change the type of the pointer somehow to short*// ...}else(...){// Change the type of the pointer somehow to char*// ...}// Read back whatever I getDWORD dwReadBack = pArray[0]; If it is impossible, and that would be my guess, then how do this in a 'really neat' way. I already have solutions but they all suck grace.
Lorenz
[edited by - sprinter_trueno on May 29, 2003 2:58:06 PM]
If you have void *pvArray, you cannot change what type pvArray is, but you can change how you access it.
If you want to access it as another type just use
(char *)pvArray
(short *)pvArray
(long *)pvArray
Get it?
[edited by - BeerNutts on May 29, 2003 3:04:10 PM]
If you want to access it as another type just use
(char *)pvArray
(short *)pvArray
(long *)pvArray
Get it?
[edited by - BeerNutts on May 29, 2003 3:04:10 PM]
char Array[4];void* pArray = (void*)Array;// Somewhere elseif(...){ // NOTE: This will not just get you the first element // of the array. It will get you ALL 4 elements. int iReadBack = *(int*)pArray;}else if(...){ // This will get you 2 elements short iReadBack = *(short*)pArray;}else(...){ // This will get you one. char cReadBack = *(char*)pArray;} The reason for the different size retrievals is that the array was declasred as a 4 element char array. Each char is 1 byte, so the array size is 4 bytes.
an int is 4 bytes, so by casting to an int you will be retirieving a value 4 bytes long, therefor extracting all 4 bytes of the array when derefrencing the pointer. To better understand it you have to take into account what beernuts said: "you cannot change what type pvArray is, but you can change how you access it"
say for example I have a variable
DWORD var = 0xFFFFFFFF;
that variable is chock-a-block. The value cannot have a higher number, if you add one it will roll back to 0.
If you just want to extract 1 byte from that, you can get a char pointer and point it to the variable, then when you dereference teh char pointer it will get you 1 bytes worth of data. a short will get you 2 bytes, etc...
char* pCharVar = (char*)&var
int iOneByteValue = *pCharVar;
If I''m not mistaken, iOneByteValue will have the value 0xFF inside it. One full byte, (255).
:::: [ Triple Buffer V2.0 ] ::::
quote:Original post by sprinter_trueno
Well, since you pointed out my inexperience, could you also provide me with an example ?
Would be very appreciated.
I apologize, I was having a bad morning.
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