Why is a 1 character .NET string 32 bytes in x64? -

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i've been trying figure out overhead of string in .net 4 x64. i've got far.

  • 16 byte object header x64
  • 4 bytes stringlength field (arraylength gone in .net 4)
  • (length + 1) * 2 bytes string content (utf-16, null terminated)

so you'd expect 1 character string 16 + 4 + 4 = 24 bytes. it's divisible 8 shouldn't need padding.

but when @ sizes in windbg see them taking 32 bytes. when !dumpobject them size 28 bytes, assume getting rounded 32. what's going on? there round of memory alignment happening?

i suspect first character aligned on 8-byte boundary on x64, when passed pointer unmanaged code, it's properly-aligned pointer. figures fit in the ones got measuring string size recently, leading formulae of:

32 bit: 14 + length * 2 (rounded 4 bytes)  64 bit: 26 + length * 2 (rounded 8 bytes)

so in 64 bit clr, 0-length string takes 32 bytes reckoning.


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