'fdisk-like' tool tha lists all the 4 partitions in the MBR scheme for a given file/device

disksize.c

/*
 * Public domain, do whatever you want with this.
 *
 * Build: gcc disksize.c -o disksize -std=c99 -pedantic -Wall -Wextra
 * Usage: ./disksize /dev/sdX
 */

#include <stdio.h>
#include <inttypes.h>
#include <assert.h>

#define GiB (1024*1024*1024)

struct partition_table_entry
{
	uint8_t  status;
	uint8_t  chs_addr_first_sector[3];
	uint8_t  type;
	uint8_t  chs_addr_last_sector[3];
	uint32_t lba_address;
	uint32_t num_sectors;
} __attribute__((packed));

struct mbr
{
	uint8_t trash[446];
	struct partition_table_entry pte[4];
	uint16_t boot_sig;
} __attribute__((packed));

static char *get_partition_type(int id)
{
	switch (id)
	{
		default:
			return "unknown";
			break;
		case 0x7:
			return "NTFS";
			break;
		case 0xB:
		case 0xC:
			return "FAT32";
			break;
		case 0x82:
			return "Linux swap";
			break;
		case 0x83:
			return "Linux";
			break;
	}
}

int main(int argc, char **argv)
{
	struct mbr mbr;

	if (argc < 2)
		return (-1);

	FILE *f = fopen(argv[1], "r");

	assert(f != NULL);
	assert(fread(&mbr, sizeof(mbr), 1, f) == 1);

	for (int i = 0; i < 4; i++)
	{
		printf("Partition #%d info:\n", i);
		printf("\tActive:         %d     \n" , mbr.pte[i].status != 0);
		printf("\tNum sectors:    %d     \n" , mbr.pte[i].num_sectors);

		printf("\tPartition type: 0x%x (%s)\n" ,
			mbr.pte[i].type, get_partition_type(mbr.pte[i].type));

		printf("\tPartition size: %.2f (GiB)\n",
			((double)(mbr.pte[i].num_sectors * 512ULL))/GiB);
	}

	fclose(f);
}