for ( i = 0 ; i < 1000000 ; i++ ) {
  char *p = malloc( 100 );
  free( p );
}

good - it automatically frees all objects created by alloca calls when
         the function making those calls exits
 
good - it is about 100X faster than malloc
 
bad - it allocates from stack, not heap.  stack space size limits
       are nowhere near a generous
bad - it is REALLY easy to reference a pointer to garbage 
       or trash the  stack of another function

 
#include <stdlib.h>
#include <time.h>
#include <sys/resource.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>     
#include <alloca.h>
#define MAX 100000
void foo(void)
{
	int i=0;
	char *p[MAX]={NULL};
	for ( i = 0 ; i < MAX ; i++ )
		p[i] = malloc( rand()%456 );
	for ( i = MAX ; i>0 ; i-- )free( p[i] );
 
}
int foo1(void)
{
	int i=0;
	char *p[MAX]={NULL};
	for ( i = 0 ; i < MAX ; i++ )
		p[i] = alloca( rand()%456 );	
}
 
void badfoo(void)
{
	int i=0;
	char *p[MAX]={NULL};
	for ( i = 0 ; i < MAX ; i++ )
		p[i] = malloc( rand()%456 );
}
 
void process(struct rusage *p, char *when)
{
	printf("%s\n", when);
	printf(" /* user time used */                   %8d  %8d\n",  p->ru_utime.tv_sec,p->ru_utime.tv_usec   );
	printf(" /* system time used */                 %8d  %8d\n",  p->ru_stime.tv_sec,p->ru_stime.tv_usec   );
	printf(" /* integral shared memory size */      %8d\n",  p->ru_ixrss           );
	printf(" /* integral unshared data  */          %8d\n",  p->ru_idrss           );
	printf(" /* integral unshared stack  */         %8d\n",  p->ru_isrss           );
 
}
 
 
int main()
{
	  int ret=0;
	  int i=0;
	  int who= RUSAGE_SELF;
	  struct rusage usage;
	  struct rusage *p=&usage;
 
	  ret=getrusage(who,p);
	  process(p, "-------------before we run foo");
	  foo();
	  ret=getrusage(who,p);
	  process(p, "\n\n-------------after we run foo");
	  for (i=0;i<10;i++)
	  {
	      foo1();
	      ret=getrusage(who,p);
	      process(p, "\n\n-------------after we run foo1");
      }	      
      badfoo();
      ret=getrusage(who,p);
	  process(p, "\n\n-------------after we run badfoo");
	return 0;
}