C can't allocate enough memory

Question

Below code doesn't give any allocation error , however the counting ends at about 16970 with memory allocation error and system halted ,I use Turbo C++ 3.0 IDE ,Windows XP sp3 , all partitions : NTFS ,PC : Dell 1545 with 2 GB ram installed .

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

long counter=0;
int main(int argc, char *argv[])
    {
        char* array=(char*) malloc (1024*1024*10);
        if (array==NULL) 
            {
                /* allocation error */
                return 1;
            }
         for (counter=0 ; counter<10000000;counter++)
         array[counter] = 1;  // trying to fill the array with one's
        free (array);
        return 0;
    }

@Meninx: in what universe would this be? `1024*1024*10 -> 10,485,760`, which most definitely not smaller than `10,000,000` — Marc B, Aug 12 '16 at 21:16
any reason you're specifying a char array, and then filling it with integers? — Marc B, Aug 12 '16 at 21:18
I see now that you are using a `C++` compiler, that's why you need to cast `malloc` — Michi, Aug 12 '16 at 21:18
Turbo C++ 3.0 is very old. Is it possible that its `int`s are only 16 bits wide? — Adrian McCarthy, Aug 12 '16 at 21:20
Try printing the evaluation of `1024*1024*10` and see if it is what you expect. — Weather Vane, Aug 12 '16 at 21:21
What @WeatherVane said... my bet is that 1024*1024*10 wrapped due to a 16-bit int. — Mike Andrews, Aug 12 '16 at 21:23
From wikipedia: *Turbo C++ 3.0 was released in 1991* - It's even older than I though... — Eugene Sh., Aug 12 '16 at 21:26
If `malloc`'s `size_t` argument is greater then 16 bits, and your `int` is 16-bits, you should cast the multiplication like `(size_t)1024*1024*10`. Assuming Turbo C has a `size_t` otherwise use `(long)1024*1024*10`. — Weather Vane, Aug 12 '16 at 21:32
possible duplicate of [this question](http://stackoverflow.com/questions/1658579/c-memory-allocation-why-there-is-not-enough-memory250k-only?rq=1) — learning_frog, Aug 12 '16 at 21:32
@Gustavo that question is related, but the issue here is that the compiler truncates 1024*1024*10 to a 16-bit integer as 0. Malloc isn't running out of memory trying to allocate a large space, instead it's being told to allocate zero memory. — Neil, Aug 12 '16 at 21:39

score 4 · Answer 1 · answered Aug 12 '16 at 21:37

4

Turbo C++ worked in a DOS environment, in real mode unless you specifically enable protected mode. In real mode, memory space is broken into 64kbyte segments, and size_t (the parameter for malloc) could easily be 16 bits. 1024*1024*10 mod 65536 = 0, so the call to malloc above works out to malloc(0).

The return value of malloc(0) is implementation-defined, and may be nonzero. (what does malloc(0) return?) Using the returned pointer would be a bad idea, and Windows XP might be intervening with the memory allocation error.

answered Aug 12 '16 at 21:37

Neil

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( 1024*1024*10 mod 65536 = 0, so the call to malloc above works out to malloc(0) ) ,, this should return a 'NULL' pointer , but that wouldn't happen ! – Howard Aug 12 '16 at 21:46
so , the problem here is in the TC++ compiler ? then , should I replace it ? – Howard Aug 12 '16 at 21:56
@howard Yes, you should replace this compiler with something newer. (And you should probably replace Windows XP with something newer, while you're at it. ;-) – zwol Aug 13 '16 at 00:02
what about 'farmalloc' ? at all I should finish this project with ms dos compilers – Howard Aug 13 '16 at 05:59
@Howard: `malloc(0)` is allowed to return a valid pointer to zero bytes of memory. – Nisse Engström Aug 13 '16 at 07:38

C can't allocate enough memory

1 Answers1