String vs. StringBuilder

Question

I understand the difference between String and StringBuilder (StringBuilder being mutable) but is there a large performance difference

Answer 1

I have seen significant performance gains from using the EnsureCapacity(int capacity) method call on an instance of StringBuilder before using it for any string storage. I usually call that on the line of code after instantiation. It has the same effect as if you instantiate the StringBuilder like this:

var sb = new StringBuilder(int capacity);

This call allocates needed memory ahead of time, which causes fewer memory allocations during multiple Append() operations. You have to make an educated guess on how much memory you will need, but for most applications this should not be too difficult. I usually err on the side of a little too much memory (we are talking 1k or so).