Weird malloc behaviour

Dear all,

I am programming a PLC with an 80188 processor, hence I am using an
old version of Borland C++ (3.10). While doing the job, I've
encountered strange behaviours and I've isolated the problem that
seems to be related to a malloc function. I wrote a little piece of
code to reproduce the situation:

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

typedef struct {
int a;
int b;
} BEAM_PRFILE;


int main(void){

BEAM_PRFILE * bpp;
int i;

bpp=(BEAM_PRFILE *)malloc(sizeof(BEAM_PRFILE));
printf("Memory was allocated at address %.8X\n", bpp);

bpp=(BEAM_PRFILE *)malloc(sizeof(BEAM_PRFILE));
printf("Memory was allocated at address %.8X\n", bpp);
}

When I use the small memory model, everything runs smoothly. The
problem is when I use the Large memory model. In this case the program
output is the following:

C:\BCTEST>tstmall
Memory was allocated at address 00000004
Memory was allocated at address 00000004

Every call to malloc returns exactly the same address (not null). I've
verified that the sizeof(BEAM_PRFILE * ) is 4 bytes with the large
memory model and 2 bytes with the small memory model, so I really
cannot figure out where the problem is

Hope you have some clue about it

Regards

Nicola

, I followed your suggestions and edited the code like this:

///////////////////////////////////////////////////////////////

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



typedef struct {
int a;
int b;
int c;
} BEAM_PRFILE;


void main(void){

BEAM_PRFILE * bpp;
unsigned long lpp;


printf("sizeof(*BEAM_PRFILE) is %d\n", sizeof(BEAM_PRFILE*));
printf("sizeof(lpp) is %d\n", sizeof(lpp));

bpp=malloc(sizeof(BEAM_PRFILE));
lpp=(unsigned long)bpp;

printf("Memory was allocated at address(X mod.) %.8X\n", bpp);
printf("Memory was allocated at address(p mod.) %p\n", bpp);

bpp=malloc(sizeof(BEAM_PRFILE));
printf("Size of the pointer is %d\n", sizeof(bpp));
lpp=(unsigned long)bpp;

printf("Memory was allocated at address %.8X\n", bpp);
printf("Memory was allocated at address(p mod.) %p\n", bpp);

}

///////////////////////////////////////////////////////////////////////////////////

The result, using the Large memory model, is the following:

C:\PACIFIC\SRC>tstmall
sizeof(*BEAM_PRFILE) is 4
sizeof(lpp) is 4
Memory was allocated at address(X mod.) 00000004
Memory was allocated at address(p mod.) 1DD5:0004
Size of the pointer is 4
Memory was allocated at address 00000004
Memory was allocated at address(p mod.) 1DD6:0004

With the small one, instead, I have the following

C:\PACIFIC\SRC>tstmall
sizeof(*BEAM_PRFILE) is 2
sizeof(lpp) is 4
Memory was allocated at address(X mod.) 00000672
Memory was allocated at address(p mod.) 0672
Size of the pointer is 2
Memory was allocated at address 0000067C
Memory was allocated at address(p mod.) 067C


So now things seem to work fine for the both of them. Now I am just
wondering why it takes to different segments to allocate a structure
which is only four bytes long, but i guess this has something to do
with the memory management model of the compiler

By the way, thanks to everyone for your precious help!!!

Regards
Nicola