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55 lines
2.6 KiB
Markdown
55 lines
2.6 KiB
Markdown
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# basic_json::number_float_t
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```cpp
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using number_float_t = NumberFloatType;
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```
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The type used to store JSON numbers (floating-point).
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[RFC 8259](https://tools.ietf.org/html/rfc8259) describes numbers as follows:
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> The representation of numbers is similar to that used in most programming languages. A number is represented in base
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> 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may
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> be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that
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> cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.
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This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is
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known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different
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types, [`number_integer_t`](number_integer_t.md), [`number_unsigned_t`](number_unsigned_t.md) and `number_float_t` are
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used.
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To store floating-point numbers in C++, a type is defined by the template parameter `NumberFloatType` which chooses the
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type to use.
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## Notes
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#### Default type
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With the default values for `NumberFloatType` (`double`), the default value for `number_float_t` is `#!cpp double`.
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#### Default behavior
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- The restrictions about leading zeros is not enforced in C++. Instead, leading zeros in floating-point literals will be
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ignored. Internally, the value will be stored as decimal number. For instance, the C++ floating-point literal `01.2`
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will be serialized to `1.2`. During deserialization, leading zeros yield an error.
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- Not-a-number (NaN) values will be serialized to `null`.
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#### Limits
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[RFC 8259](https://tools.ietf.org/html/rfc8259) states:
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> This specification allows implementations to set limits on the range and precision of numbers accepted. Since software
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> that implements IEEE 754-2008 binary64 (double precision) numbers is generally available and widely used, good
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> interoperability can be achieved by implementations that expect no more precision or range than these provide, in the
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> sense that implementations will approximate JSON numbers within the expected precision.
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This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note values
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smaller than `-1.79769313486232e+308` and values greater than `1.79769313486232e+308` will be stored as NaN internally
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and be serialized to `null`.
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#### Storage
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Floating-point number values are stored directly inside a `basic_json` type.
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## Version history
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- Added in version 1.0.0.
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