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In this article, the editor introduces in detail "how to solve the double problem in JsonCpp". The content is detailed, the steps are clear, and the details are handled properly. I hope this article "how to solve the double problem in JsonCpp" can help you solve your doubts.

Values in the json file

Program code

New_item ["Voltage"] = 8.622 ["Current"] = 8.63456 ["Energy"] = 8.234234

Program running result

In the json_write.cpp of Jsoncpp

Std::string valueToString (double value, bool useSpecialFloats, unsigned int precision) {/ / Allocate a buffer that is more than large enough to store the 16 digits of / / precision requested below. Char buffer [32]; int len =-1; char formatString [6]; sprintf (formatString, "%.% dg", precision); / / Print into the buffer. We need not request the alternative representation / / that always has a decimal point because JSON doesn't distingish the / / concepts of reals and integers. If (isfinite (value)) {len = snprintf (buffer, sizeof (buffer), formatString, value);} else {/ / IEEE standard states that NaN values will not compare to themselves if (value! = value) {len = snprintf (buffer, sizeof (buffer), useSpecialFloats? "NaN": "null");} else if (value

< 0) { len = snprintf(buffer, sizeof(buffer), useSpecialFloats ? "-Infinity" : "-1e+9999"); } else { len = snprintf(buffer, sizeof(buffer), useSpecialFloats ? "Infinity" : "1e+9999"); } // For those, we do not need to call fixNumLoc, but it is fast. } assert(len >

= 0); fixNumericLocale (buffer, buffer + len); return buffer;}

Here the result of sprintf (formatString, "%.% dg", precision); is ".17g". Is a valid number that outputs 17 digits. Insufficient to make up for 17.

The problem of decimal accuracy and insertion and output order of ps:JsonCpp

To put it bluntly, these two problems cannot be solved, as follows:

Officially, the number of decimal places is not supported. The default width of decimal places is 17 places, such as "value": 7.0999999999999996

Officially, output is not supported in insertion order, but in alphabetical order of key. No matter what order you insert, the following output is in this order:

"avg_abcdd": 1.16326400000014, "avg_pxczzczxczxd": 7.0999999999999996, "avg_shczxcdize": 802000.0, "deviccxz": "shebei25", "sh423423fd": 1420, "vcxzcasdasdadczco": 231

Personal emergency idea

For the problem of digital accuracy, you can consider converting it into the precision you need in C++, and then putting it into json as a string. As for the subsequent parsing, you can read the string and then convert it to a number.

Order question, two ideas:

1) do not use key, use the form of append, that is, put each item in a container

Json::Value res; std::string = entry_str; entry_str.append ("zhangsan,123"); entry_str.append ("abc,2596"); Res ["entry"] = entry_str

2) then order by name, comply with the rules, 2333333

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