dynamic memory allocation question

Mark Mara

This is probably a newbie c question, but I am using propgcc. How should the arguments to malloc and free be defined as to not generate warning messages from the compiler? It seemed that this should work?

#include <propeller.h>


int main(void)
{
    void        *memptr;
    memptr = (void *) malloc(10);
    free(memptr);
    return 0;
}

But I get this

Project Directory: /Users/mam1/Git/play/


propeller-elf-gcc -v GCC 4.6.1 (propellergcc_v1_0_0_2224)
propeller-elf-gcc -I . -L . -o cmm/play.elf -Os -mcmm -Wall -m32bit-doubles -fno-exceptions -std=c99 play.c
play.c: In function 'main':
play.c:10:5: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
play.c:10:23: warning: incompatible implicit declaration of built-in function 'malloc' [enabled by default]
play.c:11:5: warning: implicit declaration of function 'free' [-Wimplicit-function-declaration]
play.c:11:5: warning: incompatible implicit declaration of built-in function 'free' [enabled by default]
propeller-load -s cmm/play.elf
propeller-elf-objdump -h cmm/play.elf
Done. Build Succeeded!


propeller-load -S1 -Dreset=dtr -I /opt/parallax/propeller-load/ cmm/play.elf -r -p /dev/cu.usbserial-004213FAPropeller Version 1 on /dev/cu.usbserial-004213FA
Loading cmm/play.elf to hub memory
2648 bytes sent


Verifying RAM ... 
OK

Thanks for your help.

--markM

DavidZemon

I believe

implicit declaration of function

is the warning that says "you haven't included a header file!!!"

As per http://www.cplusplus.com/reference/cstdlib/malloc/, I would try adding

#include <stdio.h>

to your program.

jazzed

#include <stdlib.h>

http://man7.org/linux/man-pages/man3/malloc.3.html

Also void* is probably not the type you want to use.

Mark Mara

Thanks for the suggestion, but adding an include for stdio.h did not change the warning messages.

DavidZemon

Ah yea... stdlib, not io lol

Mark Mara

It was stdlib.h that I needed. Thanks

Tor

And one more thing - don't cast malloc(), if you need to cast (because you see warnings) it's telling you that the prototype is missing, i.e. missing <stdlib.h>.
So, your example

   void  *memptr;
   memptr = (void *) malloc(10); 

should be

   void   *memptr;
   memptr = malloc(10);

although a more useful and more typical example would be for example

   char *a;
   struct mystruct *rec;
   a = malloc (10);
   rec = malloc (10 * sizeof(*rec)); /* for example. Some would use sizeof (struct mystruct) */

In old K&R C, before the 'void' type was invented, 'malloc' was defined as returning a char pointer, and one would always have to cast malloc. In ANSI C 'malloc' returns a void pointer, it maps to anything and no cast is needed or wanted (and can even create subtle bugs if <stdlib.h> is missing)

-Tor