Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Round-trip format specifier incorrect for some doubles on some x64 computers #5168

hickford opened this issue Feb 23, 2016 · 2 comments


Copy link

@hickford hickford commented Feb 23, 2016

Reproduced from

Recently I have had to serialize a double into text, and then get it back. The value seems to not be equivalent:

double d1 = 0.84551240822557006;
string s = d1.ToString("R");
double d2 = double.Parse(s);
bool s1 = d1 == d2;
// -> s1 is False

But according to MSDN: Standard Numeric Format Strings, the "R" option is supposed to guarantee round-trip safety.

The round-trip ("R") format specifier is used to ensure that a numeric value that is converted to a string will be parsed back into the same numeric value

Why did this happen?

Copy link

@appel1 appel1 commented Feb 27, 2017

According to there are programs that rely on this behavior and the documentation has been updated with a workaround that you should implement R yourself for x64. Unfortunately that workaround does not work in practice since there are many places like XmlConvert where it is not possible to override how doubles are formatted.


@tannergooding tannergooding self-assigned this Sep 11, 2018
Copy link

@tannergooding tannergooding commented Feb 1, 2019

Now that dotnet/coreclr#22040 is merged, for .NET Core 3.0, ToString(), ToString("G"), ToString("R"), double.ToString("G17"), and float.ToString("G9") should now always produce a string that will roundtrip to the original value..

I will keep this open until an explicit testcase for 0.84551240822557006 can be added to CoreFX.


@danmoseley danmoseley closed this Feb 4, 2019
@msftgits msftgits transferred this issue from dotnet/coreclr Jan 30, 2020
@msftgits msftgits added this to the Future milestone Jan 30, 2020
@tannergooding tannergooding removed their assignment May 26, 2020
@msftbot msftbot bot locked as resolved and limited conversation to collaborators Jan 2, 2021
Sign up for free to subscribe to this conversation on GitHub. Already have an account? Sign in.
None yet
None yet
Linked pull requests

Successfully merging a pull request may close this issue.

4 participants