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Editorial Team
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Asked: 2026-05-29T03:37:48+00:00

I need to write a C# string to a preallocated unmanaged buffer encoded as

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I need to write a C# string to a preallocated unmanaged buffer encoded as Utf8. Before answering, please read the following requirements:

  • No new allocations (so please, don’t direct me to answers involving creating byte arrays or other instantiations)
  • No transitions to unmanaged code (no pinvoke/calli)

Currently, I’m using OpCodes.Cpblk to copy raw strings from C# to unmanaged buffers using 16 bit characters. This gives me roughly the same performance as using unmanaged memcpy on an x64 architecture and I really need the throughput to be close to that.

I am considering fixing the string as a char* and iterating over it, but implementing an encoder without jump tables would be both cumbersome and less than optimal when it comes to performance.

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1 Answer

  1. Editorial Team

    Use the unsafe overload

    public override unsafe int GetChars(byte* bytes, int byteCount, char* chars, int charCount)

    of the UTF8Encoding-class. You need to specify pointers to the string and the byte-buffer that will receive the chars. It will copy UTF-8 chars into it. No allocations will be happening but it will require unsafe code.

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