C - Allocating dynamic memory for integer and using it

Question

i am trying to allocate memory for integer but i get a warning assignment makes integer from pointer without a cast and when i do a cast for an int i get a warning cast from pointer to integer of different size

here is my code for first :

int i;
for(i = 0 ; i < gNumOfAllFiles ; i++)
{
    int *v=(int *)malloc(1*sizeof(int));
    v=0;
    dependencies[i].visited =(int)v;
}

or

dependencies[i].visited =v

The dependencies[i] is a struct contains field int visited and i am trying to initilize it by 0

Writting to a pointer: *v = 0. Reading from a pointer: visited = *v. — Guilherme Bernal
– Guilherme Bernal, Commented Nov 11, 2013 at 14:47
Why are you trying to assign a pointer-to-int to an int? What's your intent? — user529758
– user529758, Commented Nov 11, 2013 at 14:47
This code will leak memory: if gNumOfAllFiles is 1000, you'll allocate 1000 ints, but never free them. For each malloc call, there has to be a free to match it — Elias Van Ootegem
– Elias Van Ootegem, Commented Nov 12, 2013 at 13:06

grasshopper · Accepted Answer · 2013-11-11 15:14:12Z

5

This is wrong because it tries to cast the pointer address as an integer:

dependencies[i].visited =(int)v;

Do this instead (to get the contents pointed at by v):

dependencies[i].visited =*v;

edit: also, to set the contents of the pointer use *v=0; instead of v=0;

edited Nov 11, 2013 at 15:14

answered Nov 11, 2013 at 14:47

grasshopper

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Comments

SLaks · Accepted Answer · 2013-11-11 14:47:44Z

1

v contains the address of a piece of memory.
(int)v casts this address to an integer, which is a mostly-meaningless operation.

You want to get the value that occupies the memory at this address, using the dereference operator:

int value = *v;

Similarly, v = 0 makes your pointer point to memory address 0 (which is NULL), and leaks the memory you allocated using malloc().

You can store a value in the memory pointed to by the pointer using the dereference operator:

*v = 0;

answered Nov 11, 2013 at 14:47

SLaks

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Comments

user1814023 · Accepted Answer · 2013-11-11 14:47:51Z

0

use dependencies[i].visited =*v;

answered Nov 11, 2013 at 14:47

user1814023

1 Comment

easuter Over a year ago

dependencies[i].visited =*v; isn't exactly a good idea right after he assigns v = 0...

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