Programming Forums > Application Development > C

sparda · Sep 26th, 2005, 2:29 PM

I've been learning C for some time, but now im stuck! I try to compile this simple source code but i get errors.

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

int main()
{
     int *ptr;
     ptr = (*int)malloc(sizeof(int)*5);
     return 0;
}

I think it has to do with TYPE casting the int. I've switched it, and it works. For example:

incorrect: (*int)
correct: (int*).

My question is. What ways is the correct way to TYPE cast?
im guessing (int*) is the correct way, but then i again, i've seen it use as (*int). Im very confused. someone please help.

Benoit · Sep 26th, 2005, 2:51 PM

(int *)...malloc() returns a void pointer which you must typecast

Animatronic · Sep 26th, 2005, 6:25 PM

I dont know where you've seen *int but in C (and C++) it should be int*, whether you are casting to or declaring an int pointer.

If you are using a C compiler and you have included stdlib.h, there is no need to cast the result from malloc() (calloc,realloc,...), infact it can cover up serious bugs (see here for more info).

jim mcnamara · Sep 27th, 2005, 4:48 PM

casting malloc is a holdover from pre C89 compilers. When you do that you mask errors, important errors.

PS: you should check to be sure ptr is not NULL after the malloc call. malloc returns NULL when it hits a memory error.

susam_pal · Sep 27th, 2005, 11:04 PM

(* int) is incorrect!

Serinth · Sep 28th, 2005, 8:56 AM

you don't need to type cast anymore like Animatronic said, saves you alotta trouble.

Ringo · Sep 29th, 2005, 4:12 AM

Thats an excellent link anmatronic. It's bookmarked!

As it says, most experienced programmers use "p = malloc ( n * sizeof *p );"

I may have added a few parenthesis ie. sizeof(*p) but this makes perfect sense. It's completely portable and you aren't covering up the potential problem you will mask by casting (ie an error if you haven't added stlib.h).

Sep 26th, 2005, 2:29 PM	#1
sparda Newbie Join Date: Apr 2005 Location: US Posts: 15 Rep Power: 0	Question regarding Malloc() and Type casting I've been learning C for some time, but now im stuck! I try to compile this simple source code but i get errors. (Toggle Plain Text) #include <stdio.h> #include <stdlib.h> int main() { int ptr; ptr = (int)malloc(sizeof(int)5); return 0; } #include <stdio.h> #include <stdlib.h> int main() { int ptr; ptr = (int)malloc(sizeof(int)5); return 0; } I think it has to do with TYPE casting the int. I've switched it, and it works. For example: incorrect: (int) correct: (int). My question is. What ways is the correct way to TYPE cast? im guessing (int) is the correct way, but then i again, i've seen it use as (int). Im very confused. someone please help.

Sep 26th, 2005, 2:51 PM	#2
Benoit Expert Programmer Join Date: Sep 2004 Location: Ontario, Canada Posts: 555 Rep Power: 5	(int *)...malloc() returns a void pointer which you must typecast __________________ Johnny was a chemist's son but Johnny is no more, for what Johnny thought was H2O was H2SO4

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Sep 26th, 2005, 6:25 PM	#3
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	I dont know where you've seen int but in C (and C++) it should be int, whether you are casting to or declaring an int pointer. If you are using a C compiler and you have included stdlib.h, there is no need to cast the result from malloc() (calloc,realloc,...), infact it can cover up serious bugs (see here for more info).

Sep 27th, 2005, 4:48 PM	#4
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	casting malloc is a holdover from pre C89 compilers. When you do that you mask errors, important errors. PS: you should check to be sure ptr is not NULL after the malloc call. malloc returns NULL when it hits a memory error.

Sep 27th, 2005, 11:04 PM	#5
susam_pal Encoder Join Date: Sep 2005 Location: India Posts: 12 Rep Power: 0	(* int) is incorrect!

Sep 28th, 2005, 8:56 AM	#6
Serinth Programmer Join Date: Sep 2005 Posts: 50 Rep Power: 4	you don't need to type cast anymore like Animatronic said, saves you alotta trouble.

Sep 29th, 2005, 4:12 AM	#7
Ringo Newbie Join Date: Sep 2005 Location: Cambridge, UK Posts: 13 Rep Power: 0	Thats an excellent link anmatronic. It's bookmarked! As it says, most experienced programmers use "p = malloc ( n * sizeof p );" I may have added a few parenthesis ie. sizeof(p) but this makes perfect sense. It's completely portable and you aren't covering up the potential problem you will mask by casting (ie an error if you haven't added stlib.h).

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Programming Forums > Application Development > C

Question regarding Malloc() and Type casting