Which is faster/preferred: memset or for loop to zero out an array of doubles?

Question

double d[10]; int length = 10;  memset(d, length * sizeof(double), 0);  //or  for (int i = length; i--;)   d[i] = 0.0; 

Answer 1

If you really care you should try and measure. However the most portable way is using std::fill():

std::fill( array, array + numberOfElements, 0.0 ); 

Answer 2

Note that for memset you have to pass the number of bytes, not the number of elements because this is an old C function:

memset(d, 0, sizeof(double)*length); 

memset can be faster since it is written in assembler, whereas std::fill is a template function which simply does a loop internally.

But for type safety and more readable code I would recommend std::fill() - it is the c++ way of doing things, and consider memset if a performance optimization is needed at this place in the code.