c# - How does the StringBuilder decide how large its capacity should be? -

i know stringbuilder object allocates more memory when use sb.append(..) when sb @ capacity. how capacity increase?

    stringbuilder sb = new stringbuilder(5);     sb.append("0123456789"); 

now capacity of sb , why? multiplier?

just clarity. asking capacity , not length.

thanks!

the capacity doubles each time apart special cases:

• if doubling not enough capacity further increased exact amount required.
• there upper limit - 0x7fffffff.

you can see algorithm using .net reflector or downloading reference source.

i can't post source code official .net implementation here's code mono implementation:

// try double buffer, if doesn't work, set length capacity if (size > capacity) {      // first time string appended, set _cached_str     // , _str it. allows optimizations.     // below, take account.     if ((object) _cached_str == (object) _str && capacity < constdefaultcapacity)         capacity = constdefaultcapacity;      capacity = capacity << 1;  // means "capacity *= 2;"      if (size > capacity)         capacity = size;      if (capacity >= int32.maxvalue || capacity < 0)         capacity = int32.maxvalue;      if (capacity > _maxcapacity && size <= _maxcapacity)         capacity = _maxcapacity; } 

i recommend don't write code relies on specific algorithm implementation detail, , not guaranteed interface.