#include <stdio.h>

int main (int argc, char * argv []) {
    if (argc != 3) {
	printf("usage: %s <source> <destination>\n", argv[0]);
	return 1;
    }
    FILE * src = fopen(argv[1], "r");
    if (src == 0)  {
	printf("could not open source file %s\n", argv[1]);
	return 1;
    }

    FILE * dst = fopen(argv[2], "w");
    if (dst == 0)  {
	printf("could not open destination file %s\n", argv[2]);
	fclose(src);
	return 1;
    }
    static const unsigned int BLOCK_SIZE = 1024; 
    char buffer[BLOCK_SIZE];

    size_t res;
    while ((res = fread(buffer, 1, BLOCK_SIZE, src)) > 0) {
	do {
	    char * buf_w_pos = buffer;
	    size_t w_res = fwrite(buf_w_pos, 1, res, dst);
	    if (w_res == 0) {
		printf("could write onto destination file %s\n", argv[2]);
		fclose(src);
		fclose(dst);
		return 1;
	    }
	    buf_w_pos += w_res;
	    res -= w_res;
	} while (res > 0);
    }
    fclose(src);
    fclose(dst);
}