reintepret_cast

hey guys,
i was doing this examples given on the book when i encountered this problem on reintepet_cast although i guess its not on that topic.. help me :(

Code:

---

#include <iostream.h>

#include <stdlib.h>

using namespace std;

const int sz = 10;

struct X { int a[sz]; };

void print(X* x) {

  for(int i = 0; i < sz; i++)

    cout << x->a[i] << ' ';

  cout << endl << "--------------------" << endl;

}

int main() {

  X x;

  print(&x);

  int* xp = reinterpret_cast<int*>(&x);

  for(int* i = xp; i < xp + sz ; i++)
// hey why is this  xp  + sz here ???
// i didnt get this.
//rest is fine with me ;)

    *i = 0;
 
print(reinterpret_cast<X*>(xp));
 
system("pause");

}

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Code tags added by Hammer

Its a pretty scuzzy way of accessing structure contents...

int* xp = reinterpret_cast<int*>(&x);

Take the address of the start of the struct (which is filled with ints in an array) and cast it to an int pointer......reasoning being that if you deference this pointer it will give you the first int in the array.

for(int* i = xp; i < xp + sz ; i++)

Now iterate up the memory by the size of an int each time (basically walk the array of ints)...

why this xp+xz ???
i got the rest of the part.. iterating and all that.thanx alot.
for(int* i = xp; i < xp + sz ; i++)

xp is the first in in the array.....and the array is sz ints long....so as i starts at xp, it can be incremented sz times before the i < xp + sz test returns false

doesnt this statement

int* xp = reinterpret_cast<int*>(&x);

makes xp = address of x ???

for(int* i = xp; i < xp + sz ; i++)

well here in the loop xp's value is in hex and sz is in decimal. how

can they be resolved??

i am just a beginner so be patient with me ;)

Please use code tags when posting code.

i mean how can they be added hex + decimal??

Quote:

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Originally posted by newbie_grg
i mean how can they be added hex + decimal??

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Its not Hex + Decimal...its memory and offset

You do that every time you use an array

int x[10];

//------ Fill array

int y = x [3];//x is a memory location and you add 3 * sizeof(int).

so xp + sz is sz ints after xp...which takes it after the end of the array, so as sson as you are about to access the variable after the array it stops.

The computer can add decimal and hex together because everything is actually stored in binary. The decimal or hex format is a conversion for input / output.

You could add a decimal number to a hex number, right? I could say add 10 decimal to A hex and give me the answer in decimal... then give me the answer in hex.