Possible to limit precision of number types?

[richardeakin]

I have a json-based config where I write some parameters, and when my application closes it uses the Json::StyledWriter to save the latest state of my root Json::Value object. I understand that round trip floating point precision isn't guaranteed to be exact, but is there a way to avoid numbers such as 0.15 being saved as 0.14999999999999999? This makes the config file difficult to read.

One solution I was wondering about is whether I could limit the precision of floating point numbers, I rarely in this case want more than 4 significant decimals and that would at least improve the use case.

[cdunn2001]

First, please use StreamWriterBuilder. That allows us to add extra configuration without breaking binary-compatibility.

Note that, as described in issue #98, you will not have round-trip reproducibility if you have fewer than 17 digits of precision. Despite that caveat, we could add a setting to limit the precision. However, I don't have time right now, but if you submit a PR, we could pull it.

[bknecht]

I saw you just closed this issue I'm interested in. What's the resolution? I just had a quick look at the code of StreamWriterBuilder and I think it's not too difficult to do. Is your request for a PR still open? I'll sit down and have a try at it if you're still interested.

[cdunn2001]

Great!

[longlene]

I think the reason of this problem is that: jsoncpp library use the double type to present the float-point number.
The double type use IEEE-754 standard, which may cause precision lose.

[cdunn2001]

That makes sense. Thanks.

[shuhongwang-zzu]

anyone help?

[dota17]

anyone help?

see the PR #381

[shuhongwang-zzu]

anyone help?

see the PR #381
Maybe the version of jsoncpp is inconsistent, mine is
JSONCPP_STRING valueToString(double value,
unsigned int precision,
PrecisionType precisionType) {
return valueToString(value, false, precision, precisionType);
}
can you help me again?