Pointer Increment

[ranjeet.gupta]

Dear All,

Which is correct ?

Let suppose we allocate the memory for the 100 bytes,

int *PtrMemoryBlock = (int *)malloc(100);

If I do

PtrMemoryBlock = PtrMemoryBlock + 10;

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?

Thanks in advance
Ranjeet

[Richard Bos]

ra***********@g mail.com wrote:

Which is correct ?
Neither, as usual.
Let suppose we allocate the memory for the 100 bytes,

int *PtrMemoryBlock = (int *)malloc(100);
This is not the right way to call malloc().
If I do

PtrMemoryBlock = PtrMemoryBlock + 10;

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?

No. It will point to the 10th int.

Richard

[Robben]

ra***********@g mail.com wrote:

Dear All,

Which is correct ?

Let suppose we allocate the memory for the 100 bytes,

int *PtrMemoryBlock = (int *)malloc(100);

If I do

PtrMemoryBlock = PtrMemoryBlock + 10;

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?
It will point to 10th integer location. int *PtrMemoryBlock = (int *)malloc(100); Assume PtrMemoryBlock = 0. PtrMemoryBlock = PtrMemoryBlock + 10; After the above operation PtrMemoryBlock will be 40.
10 * 4 = 40th byte location.
4 is the size of the integer.
10 is the increment value
Thanks in advance
Ranjeet

[kernelxu]

ranjeet.gu...@g mail.com write:

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?

neither ,
it points to memory (PtrMemoryBlock just points to) loaction of Nth
byte,
and, N = 10 * sizeof(int).
pointer "PtrMemoryBlock " is declared to point to int type, so while
doing an addition of 10 to the pointer , 10 * sizeof(int) is added in
fact.

[ranjeet.gupta]

Robben wrote:

ra***********@g mail.com wrote:

Dear All,

Which is correct ?

Let suppose we allocate the memory for the 100 bytes,

int *PtrMemoryBlock = (int *)malloc(100);

If I do

PtrMemoryBlock = PtrMemoryBlock + 10;

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?
It will point to 10th integer location.

int *PtrMemoryBlock = (int *)malloc(100);

Assume PtrMemoryBlock = 0.

PtrMemoryBlock = PtrMemoryBlock + 10;

After the above operation PtrMemoryBlock will be 40.
10 * 4 = 40th byte location.
4 is the size of the integer.
10 is the increment value

Here is the code

int main ()
{
int *MemoryBlockPtr = malloc(100);
printf("%p\n", MemoryBlockPtr) ;
MemoryBlockPtr = MemoryBlockPtr + 10;
printf("%p\n", MemoryBlockPtr) ;
return 0;
}

Thanks for your explanation as I was also wondering about the above
40, to figure out mathematically, I was able to conclude the above
conclusion, (Which you to stated)

Now as you have said and seems to me that you are confirm, then,
please let me know why multiplication is done with the size ?

Now If the normal pointer of the array is incremented then there
is no such multiplication.

Anyway Looks to me that I am missing some thing ? Please clarify.

Can we fix and point to the 10th int what is the correction factor,
Is this Universially Accepted (Correction factor is there) ????

Regards
Ranjeet

Thanks in advance
Ranjeet

[Suman]

ra***********@g mail.com wrote:

Robben wrote:

ra***********@g mail.com wrote:

Dear All,

Which is correct ?

Let suppose we allocate the memory for the 100 bytes,

int *PtrMemoryBlock = (int *)malloc(100);

If I do

PtrMemoryBlock = PtrMemoryBlock + 10;

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?
It will point to 10th integer location.

int *PtrMemoryBlock = (int *)malloc(100);

Assume PtrMemoryBlock = 0.

PtrMemoryBlock = PtrMemoryBlock + 10;

After the above operation PtrMemoryBlock will be 40.
10 * 4 = 40th byte location.
4 is the size of the integer.
10 is the increment value

Here is the code

#include <stdio.h>
#include <stdlib.h> int main ()
{
int *MemoryBlockPtr = malloc(100);
If you are trying to allocate room for say 100 integers, say so:
int *MemoryBlockPtr = malloc( 100 * sizeof *MemoryBlockPtr ); printf("%p\n", MemoryBlockPtr) ;
%p requires you to pass a pointer to void, so:
printf("%p\n", (void *)MemoryBlockPt r);
MemoryBlockPtr = MemoryBlockPtr + 10;
printf("%p\n", MemoryBlockPtr) ;
printf("%p\n", (void *)MemoryBlockPt r);
return 0;
}

Thanks for your explanation as I was also wondering about the above
40, to figure out mathematically, I was able to conclude the above
conclusion, (Which you to stated)

Now as you have said and seems to me that you are confirm, then,
please let me know why multiplication is done with the size ?
For a type T,
T array[HUGE];
T *pt = array;
pt = pt + int_offset;
is read by the compiler as
pt = pt + int_offset * sizeof *pt;
Now If the normal pointer of the array is incremented then there
is no such multiplication.
What is a normal pointer? Anyway Looks to me that I am missing some thing ? Please clarify.

Can we fix and point to the 10th int what is the correction factor,
Is this Universially Accepted (Correction factor is there) ????

Regards
Ranjeet

Thanks in advance
Ranjeet

[Robben]

ra***********@g mail.com wrote:

Robben wrote:

ra***********@g mail.com wrote:

Dear All,

Which is correct ?

Let suppose we allocate the memory for the 100 bytes,

int *PtrMemoryBlock = (int *)malloc(100);

If I do

PtrMemoryBlock = PtrMemoryBlock + 10;

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?
It will point to 10th integer location.

int *PtrMemoryBlock = (int *)malloc(100);

Assume PtrMemoryBlock = 0.

PtrMemoryBlock = PtrMemoryBlock + 10;

After the above operation PtrMemoryBlock will be 40.
10 * 4 = 40th byte location.
4 is the size of the integer.
10 is the increment value

Here is the code

int main ()
{
int *MemoryBlockPtr = malloc(100);
printf("%p\n", MemoryBlockPtr) ;
MemoryBlockPtr = MemoryBlockPtr + 10;
printf("%p\n", MemoryBlockPtr) ;
return 0;
}

Thanks for your explanation as I was also wondering about the above
40, to figure out mathematically, I was able to conclude the above
conclusion, (Which you to stated)

Now as you have said and seems to me that you are confirm, then,
please let me know why multiplication is done with the size ?

Now If the normal pointer of the array is incremented then there
is no such multiplication.

It will be the same... as array also holds location the pointer
location.
Try out!!
It completely depends on what array is holding
For char/unsigned char there will not be any multiplication as it char
size is 1.
for short it will be multiplied by 2 and so on..

Please look into Sumans comments as there is something wrong in the
sample code provided

If you are trying to allocate room for say 100 integers, say so:

int *MemoryBlockPtr = malloc( 100 * sizeof *MemoryBlockPtr );

Anyway Looks to me that I am missing some thing ? Please clarify.

Can we fix and point to the 10th int what is the correction factor,
Is this Universially Accepted (Correction factor is there) ????

Regards
Ranjeet

Thanks in advance
Ranjeet

[ahmed.mubin]

It will point to
(initial_addres s)+(num_times_t o_increment)*(s ize_of_data_typ e)

[ranjeet.gupta]

ke******@hotmai l.com wrote:

ranjeet.gu...@g mail.com write:

will it point to memory loaction of 10th byte, memroy allocated by
malloc OR it will point to the 10 + 100 (Byte Allocated by malloc)
memory loaction ?

neither ,
it points to memory (PtrMemoryBlock just points to) loaction of Nth
byte,
and, N = 10 * sizeof(int).
pointer "PtrMemoryBlock " is declared to point to int type, so while
doing an addition of 10 to the pointer , 10 * sizeof(int) is added in
fact.

Thanks to all for your quick Response, Well I cleared doubts
while going thourgh the threads, Was bit confused, but I am clear :-)
Well in one slot, I asked some REALLY Stupid Question :-)

Reagrds
Ranjeet

[Flash Gordon]

ah*********@gma il.com wrote:

It will point to
(initial_addres s)+(num_times_t o_increment)*(s ize_of_data_typ e)

What will? I suggest you read the posts that are made almost daily to
this group or read CBFalconer's sig which is on all his posts and has
instructions. Had you actually read a few days posts as you are meant to
with ALL groups before posting you would have seen these instructions.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.