Incompatible implicit declaration of built-in function ‘malloc’

Question

I'm getting this error:

warning: incompatible implicit declaration of built-in function ‘malloc’

I am trying to do this:

fileinfo_list* tempList = malloc(sizeof(fileinfo_list));

Just for the reference the struct used at hand is:

typedef struct {
    fileinfo** filedata;
    size_t nFiles;
    size_t size;
    size_t fileblock;
} fileinfo_list;

I don't see anything wrong with what I've done. I'm just creating a tempList with the size of 1 x fileinfo_list.

possible duplicate of [Why do I get a warning everytime I use malloc?](http://stackoverflow.com/questions/1230386/why-do-i-get-a-warning-everytime-i-use-malloc) — Oded, Nov 01 '11 at 14:14

score 357 · Accepted Answer · edited Feb 19 '21 at 22:42

357

You likely forgot to #include <stdlib.h>

edited Feb 19 '21 at 22:42

jasonleonhard

answered Aug 13 '11 at 13:50

cnicutar

1

ahh thanks :) still getting the hang of C, first C program coming from java :) – SGE Aug 13 '11 at 13:53
1

after including `` the warning was replaced by an error `error: conflicting types for 'malloc'` – Christos Karapapas Nov 05 '18 at 20:17

score 46 · Answer 2 · edited Dec 10 '17 at 21:37

46

You need to #include <stdlib.h>. Otherwise it's defined as int malloc() which is incompatible with the built-in type void *malloc(size_t).

edited Dec 10 '17 at 21:37

Peter Mortensen

answered Aug 13 '11 at 13:51

Omri Barel

when it is defined as `int malloc()`, does it replicate `void *malloc(size_t)`? – user1343318 Mar 12 '14 at 22:19
@user1343318 Not necessarily, which is precisely the reason for the warning. Ex: a x64 platform with 64-bit data pointers and 32-bit `int` values will puke goat feces, while a x86 32bit-data-pointer/32bit-`int` can seemingly work correctly. *Neither* are correct, as in neither case is the compiler aware of what `malloc` actually returns, and assumes `int` in response. – WhozCraig May 13 '15 at 01:54

score 15 · Answer 3 · answered Aug 13 '11 at 13:51

15

You're missing #include <stdlib.h>.

answered Aug 13 '11 at 13:51

Antti

score 4 · Answer 4 · edited Dec 10 '17 at 21:54

4

The stdlib.h file contains the header information or prototype of the malloc, calloc, realloc and free functions.

So to avoid this warning in ANSI C, you should include the stdlib header file.

edited Dec 10 '17 at 21:54

Peter Mortensen

answered Jul 25 '14 at 13:49

santosh sahu

score -4 · Answer 5 · answered Jul 11 '14 at 06:08

-4

The only solution for such warnings is to include stdlib.h in the program.

answered Jul 11 '14 at 06:08

user3828152

5 Answers5