Rounding doubles - .5 - sprintf

Question

I\'m using the following code for rounding to 2dp:

sprintf(temp,\"%.2f\",coef[i]); //coef[i] returns a double

It successfully rounds 6.666

Answer 1

How about this for another possible solution:

printf("%.2f", _nextafter(n, n*2));

The idea is to increase the number away from zero (the n*2 gets the sign right) by the smallest possible amount representable by floating point math.

Eg:

double n=5.555;
printf("%.2f\n", n);
printf("%.2f\n", _nextafter(n, n*2));
printf("%.20f\n", n);
printf("%.20f\n", _nextafter(n, n*2));

With MSVC yields:

5.55
5.56
5.55499999999999970000
5.55500000000000060000