Splits binary files in two parts.

parts.c

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

#define FTELL _ftelli64
#define FSEEK _fseeki64

void usage()
{
	puts("parts FILE OUTPUT OFFSET [LENGTH]");
}

void die(const char* msg)
{
	puts(msg);
	exit(1);
}

int main(int argc, char* argv[])
{
	if (argc < 4) {
		usage();
		return 1;
	}
	
	const char* path = argv[1];
	const char* output_path = argv[2];
	unsigned long long offset = atoi(argv[3]);
	unsigned long long length = 0;

	FILE* fp = fopen(path, "rb");
	if (!fp) die("Couldn't open input file.");
	FILE* out = fopen(output_path, "wb");
	if (!out) die("Couldn't open output file.");
	FSEEK(fp, 0, SEEK_END);
	unsigned long long size = FTELL(fp);
	FSEEK(fp, offset, SEEK_SET);

	if (argc < 5) {
		length = size - offset;
	} else {
		length = atoi(argv[4]);
	}

	char* data = malloc(length);
	if (fread(data, sizeof(char), length, fp) != length) {
		puts("Couldn't read data.");
		goto end;
	}

	if (fwrite(data, sizeof(char), length, out) != length) {
		puts("Couldn't write data.");
	}

	free(data);
	
	end:
	fclose(fp);
	fclose(out);

	return 0;
}