Zerofree (fill unused hard disk space with zeroes) for OS/2 Warp, see https://supratim-sanyal.blogspot.com/2016/12/zero-out-free-disk-space-on-virtual.html

zerofree-os2.c

/* zerofree-os2.c
   (c) 2020 Supratim Sanyal
   
   A minimal program to zero out unused disk space for OS/2 Warp and derivates
   (eComstation, ArcaOS etc.). Nothing OS/2 specific here, it should work for all
   operating systems with a C compiler once the OS/2-style (MS-DOS style) pathnames
   for drive letter and directory for the zero.zero file are adjusted.
   
   Compiled using Borland C++ 2.0 for OS/2. Executable is downloadable free from:
   https://supratim-sanyal.blogspot.com/2016/12/zero-out-free-disk-space-on-virtual.html
   
   Licensed under Beerware License 42: Absolutely no assurances, all risk is
   yours. If it does something useful and we meet some day buy me a beer.
*/

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

int main(int argc, char *argv[])
{

	FILE *fp=NULL;
	char fname[32]="\0";
	int i=0;
	int done=0;

	if (2!=argc)
	{
		fprintf(stderr,"usage: %s <drive-letter>\n",argv[0]);
		return(1);
	}

	if (1!=strlen(argv[1]))
	{
		fprintf(stderr,"usage: %s <drive-letter>\n",argv[0]);
		return(1);
	}

	sprintf(fname,"%s:\\zero.zero",argv[1]);

	printf("Creating file %s filled with zeroes ...\n",fname);

	if (NULL==(fp=fopen(fname,"w"))) {perror(fname);return 1;}

	while(!done)
	{
		for(i=0;i<(100*148576);i++)	/* mark every 100 MB */
		{
			if(EOF==fputc('\0',fp))
			{
				done=1;
				break;
			}
		}

		putchar('*');
		fflush(NULL);
	}

	putchar('\n');
	fflush(NULL);

	fclose(fp);
	fflush(NULL);

	printf("Deleting file %s ...\n",fname);

	if(0!=unlink(fname)) {perror(fname);return 1;}

	printf("Have a great life!\n");
	return(0);
}