storing address as a value

i am stuck with this one..this is what i have coded...

Code:

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int main() {
        int *var_a = malloc(sizeof(int));
        int *var_b = malloc(sizeof(int));
        int *var_c = NULL;
        *var_b = 13;
        *var_a = (int)var_b;
        var_c = (int *)(*var_a);
        printf("%d\n\n", *var_c);
        return 0;
}

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this code is giving two warnings when run on Visual Studio 2003...


the problem is that i want to store an address as an integer value!!
for e.g a pointer points to a location 0x12345
i want to store this location as an integer value in the 'value of' a pointer..
i.e. i want to store 0x12345 in *(ptr)

is there any way this can be done..

Addresses are stored in pointers, not integers. You can print pointers to void with the %p format specifier, so if you have a pointer to int, just cast it to void* when you print with say, printf().

i know they are pointers and not integers..but an address is an integer value ..and i want that integer value to be extracted from the pointer...

Quote:

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i know they are pointers and not integers..but an address is an integer value ..and i want that integer value to be extracted from the pointer...

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In that case, you should cast the pointer to int, but note that the result is implementation defined.

From what I see, your example code already does that, except that it obfuscates the issue by using pointers unnecessarily (and fails to use free() to match the malloc()). What warnings do you get? Did you remember to include <stdlib.h> and <stdio.h>?

these are the warnings that i am getting

Quote:

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warning C4311: 'type cast' : pointer truncation from 'int *' to 'long'
warning C4312: 'type cast' : conversion from 'int' to 'int *' of greater size

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and i have just missed the free() calls because i was just testing the concept as i want to use the same in one of my projects..and i did include the all the required header files..but i want a code which is stable and the compilation not giving any warnings..

Quote:

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these are the warnings that i am getting

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It would help if you gave everything so we do not have to guess the line numbers.

The problem is probably because on your system, a pointer cannot fit into an int.

Quote:

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i want to use the same in one of my projects

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Why do you need to store an address in an integer variable?

Well, I don't know why the compiler says from int * to long, since you cast to int. Just for the fun of it though, cast the integer to long to see what happens, even though pointers should be int. Try sizeof(pointer), sizeof(int) to see what happens.

My guess would be that it's a 64-bit system, which means that the pointer is 64-bits, but int is still only 32, consequently the pointer won't fit.

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Mats

@C_ntua
hehehe...i tried the 'long' thing and the warning that i quoted was after the changes itself!!

otherwise that first warning is :"warning C4311: 'type cast' : pointer truncation from 'int *' to 'int' "



@matsp
i am working on a 32 bit system only..

@laserlight
the complete code is (after i have added the'free' calls) is:

Code:

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#include <stdio.h>
#include <stdlib.h>

int main() {
        int *var_a = malloc(sizeof(int));
        int *var_b = malloc(sizeof(int));
        int *var_c = NULL;
        *var_b = 13;
        *var_a = (int)var_b;
        var_c = (int *)(*var_a);
        printf("&#37;d\n\n", *var_c);
        free(a);
        free(b);
        return 0;
}

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and the warnings are:

line(9) : warning C4311: 'type cast' : pointer truncation from 'int *' to 'int'
line(10) : warning C4312: 'type cast' : conversion from 'int' to 'int *' of greater size


and why do i need it is something i might not be able to explain in the forum..is it not possible we just look into the snippet i have given and look for the solution ..??because if i am able to compile and execute the above snippet without any warning or errors, my issue will be resolved

Quote:

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Originally Posted by technosavvy

@C_ntua
hehehe...i tried the 'long' thing and the warning that i quoted was after the changes itself!!

otherwise that first warning is :"warning C4311: 'type cast' : pointer truncation from 'int *' to 'int' "



@matsp
i am working on a 32 bit system only..

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Are you using a MS Visual C++ compiler by any chance? If so, it requires that you do special things to make sure that your code is 64-bit compatible, even when it's actually perfectly fine for 32-bit.

I get no warnings compiling your original code in gcc-mingw 3.4.2

--
Mats

for info...i am working on a 32 bit intel system with windows XP installed on it..
i am using VISUAL STUDIO 2003 IDE for testing my code.

Quote:

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Originally Posted by technosavvy

and why do i need it is something i might not be able to explain in the forum..is it not possible we just look into the snippet i have given and look for the solution ..??because if i am able to compile and execute the above snippet without any warning or errors, my issue will be resolved

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I think laserlight was wanting to know the bigger picture - just like if you are mechanic in a car workshop, and someone asks "how do I undo a bolt", it may mean that they are trying to take off the wheel to replace it with the spare wheel, in which case, knowing that and suggesting the right steps or replacing a wheel is better than just say "turn the bolt counter-clockwise" [and of course, it could be one of the rare bolts that are left-threaded, so you should actually turn it clockwise to loosen it - without knowing, the mechanic could give the completely wrong advice].

So, back to the point: you want to store a pointer in an integer, but the compiler doesn't think it's a good idea. I suppose it's a Microsoft "problem", in that there are specific types to indicate that they are compatible with pointers in both 32 and 64-bit compiles.

If instead of asking here, you googled the C4311 error code, you would have found this as the first hit:
http://msdn.microsoft.com/en-us/library/4t91x2k5.aspx

--
Mats

@matsp
i do not want my code to be 64 bit compatiable ..

@all
i have come up with the following solution, do u think there are any issue with this style of coding

Code:

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#include <stdio.h>
#include <stdlib.h>
int main() {
        int *c = NULL;
        int *a = malloc(sizeof(int));
        int *b = malloc(sizeof(int));
        *b = 13;
        *((int **)a) = b;
        c = *((int **)a);
        printf("&#37;d\n\n", *c);
        free(a);
        free(b);
        return 0;
}

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@matsp
i did see the reason for the warnings before putting my code on the forum..
i just wanted to give you guys whatever i have tried , so that there is a better understanding of what i wish to achieve ..my problem is known and i need to know the solution to it, not why even the warnings are being generated.. :)