Format a quantity in bytes into a human readable string (C)

human-size.c

#include <stdio.h> 
#include <stdlib.h> // atoll
#include <stdint.h> // uint64_t
#include <inttypes.h> // PRIu64

static const char *humanSize(uint64_t bytes)
{
	char *suffix[] = {"B", "KB", "MB", "GB", "TB"};
	char length = sizeof(suffix) / sizeof(suffix[0]);

	int i = 0;
	double dblBytes = bytes;

	if (bytes > 1024) {
		for (i = 0; (bytes / 1024) > 0 && i<length-1; i++, bytes /= 1024)
			dblBytes = bytes / 1024.0;
	}

	static char output[200];
	sprintf(output, "%.02lf %s", dblBytes, suffix[i]);
	return output;
}

int main(int argc, char **argv)
{
	if (argc == 1) {
		fprintf(stderr, "Usage: %s <bytes>\n", *argv);
		return 1;
	}

	uint64_t bytes = atoll(argv[1]);

	printf("%" PRIu64 " Bytes: %s\n", bytes, humanSize(bytes));

	return 0;
}