Realloc returns null, why?

hi everyone,

i seem have located orign of bug experiencing.
i think realloc works kind of funky. situation follows:
* allocate buffer of 2 bytes size (malloc)
* reallocate (realloc) same buffer , ask expand size of 4 bytes
* realloc method returns null

this culprit:
pulsebuffer = (unsigned int *)realloc(pulsebuffer , newsize );

but when code follows, memory allocation works ok:
   unsigned int * prevpulsebuffer = pulsebuffer;
   pulsebuffer = (unsigned int *) malloc(newsize);
   for (int idx=0;idx<pulsebufferlength;idx++) pulsebuffer[idx] = prevpulsebuffer[idx];
   free(prevpulsebuffer);

what missing?

thanks, sander

sander,

what happens when reduce problem following simple test case?

void setup()
{
 serial.begin(9600);
 void *p = malloc(2);
 serial.println((int)p, hex);
 p = realloc(p, 4);
 serial.println((int)p, hex);
}

void loop()
{}

on system, both malloc , realloc succeed, printing address 195 each.  assuming experiment succeeds you, guess have miscalculated "newsize" somehow.  if newsize 4 (print out make sure!), perhaps have consumed of memory (heap) space somewhere , that's why realloc fails.

mikal

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