[API Proposal] add ReadOnlySpan<byte> overloads to BitConverter.ToString()

Background and Motivation

BitConverter.ToString() has no overloads to accept Readonlyspan. When we got a span we have to call ToArray() first. Other BitConverter functions do have a Readonlyspan overload, such as BitConverter.ToInt32().

Proposed API

namespace System
{
    public class BitConverter {
+        public static string ToString(ReadOnlySpan<byte> value);
     }

Usage Examples

ReadOnlySpan<byte> span = BitConverter.GetBytes("hello world").AsSpan();
Console.WriteLine(BitConverter.ToString(span));

FYI we don't normally add startIndex and length parameters on APIs which take spans. The caller is expected to slice the span appropriately before calling the method.

Do you have a usage example where you're relying on BitConverter.ToString in your own code? The example you provided won't compile, even with the APIs you had proposed here.

Yes I do have but I cannot show it public. However I can show you a variation of it:

const int infoLength = 32;
byte[] infoStartingBytes = { 0xFF, 0xFF, 0xFF, 0xFF };

ReadOnlySpan<byte> span = System.IO.File.ReadAllBytes("C:\\data.dat").AsSpan();
int pos = span.IndexOf(infoStartingBytes);

while (pos != -1) {
	span = span.Slice(span.IndexOf(infoStartingBytes));
	int id = BitConverter.ToInt32(span);
	span = span.Slice(infoLength + 1);
	string name = System.Text.Encoding.UTF8.GetString(span);
	span = span.Slice(infoLength + 1);
	// couple of lines later
	string hash = BitConverter.ToString(span.Slice(infoLength).ToArray());
	span = span.Slice(infoLength + 1);
	// saving these information somewhere
	pos = span.IndexOf(infoStartingBytes);
}

Using a span has the benefit of slicing. However at one point I have to convert it back to an array when I want to use BitConverter.ToString. I wouldn't mind if there is no overload with startIndex and length parameters since this can easily applied to the span instead but I want to get rid of the additional extra allocation of ToArray(). And I asked myself why every other function of BitConverter has received a span overload but not ToString?

Thanks! I'll mark this ready for review.

Having the dashes between each byte is important to your use case?

Just want to point out that the details of the format used, dashes or not, casing, etc. was debated at length in #17837, and the decision then was to just add Convert.ToHexString that only offered the one approach of no separators, all upper-case.

we shouldn't change the behavior.

I'm not suggesting changing behavior. Convert.ToHexString already takes a span and produces a hex string, just without dashes. I was questioning whether we need another.

I'm not suggesting changing behavior. Convert.ToHexString already takes a span and produces a hex string, just without dashes. I was questioning whether we need another.

So, all of us that do require the dash* have to either change our logic (not just code), roll our own hex formatter or keep allocating (and copying) memory on the heap? Don't get me wrong, all 3 are fair, its not like our existing code got broken...
I agree that #17837 is a better forward solution, I will probably end up changing my code to use it instead myself.

If no overload is added, perhaps BitConverter.ToString should be decorated with [Obsolete("Use Convert.ToHexString where possible")] so developers that remove the '-' easily realize they don't have to anymore =].

*I personally kept the dash because didn't want the performance hit of removing them.

I'm not suggesting changing behavior. Convert.ToHexString already takes a span and produces a hex string, just without dashes. I was questioning whether we need another.

Well in my use case, I use the BitConverter.ToString method to print the hex string to the console for debug purposes. Having dashes keeps the string more readable for me. I often have to write some thing along this just for debugging:

Console.WriteLine(BitConverter.ToString(reader.ReadBytes(reader.BytesRemaining).ToArray()));

where reader.ReadBytes(numOfBytes) returns a ReadOnlySpan<byte>

I personally would appreciate adding this api.

Comment

Closing this as not planned.

As per the above, this was already debated extensively in a past API review and we opted to not go this route. There's not enough interest in this specific API and the overwhelming majority are using the APIs on Convert instead which don't involve any separator. Users who really need this and who cannot just use the existing byte[] value, int startIndex, int length overload can always copy the 20-30 lines of code required.

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[API Proposal] add ReadOnlySpan<byte> overloads to BitConverter.ToString() #50588

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[API Proposal] add ReadOnlySpan<byte> overloads to BitConverter.ToString() #50588

Description

Background and Motivation

Proposed API

Usage Examples

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GrabYourPitchforks commented on Apr 1, 2021

Symbai commented on Apr 1, 2021

GrabYourPitchforks commented on Apr 1, 2021

stephentoub commented on Apr 1, 2021

stephentoub commented on Apr 1, 2021

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stephentoub commented on Apr 2, 2021

XArtur0 commented on Jun 17, 2021

msschl commented on Aug 25, 2021

Symbai commented on Feb 28, 2026

tannergooding commented on Apr 3, 2026

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