76 lines
2.9 KiB
Markdown
76 lines
2.9 KiB
Markdown
|
# basic_json::number_unsigned_t
|
||
|
|
|
||
|
|
```cpp
|
||
|
|
using number_unsigned_t = NumberUnsignedType;
|
||
|
|
```
|
||
|
|
|
||
|
|
The type used to store JSON numbers (unsigned).
|
||
|
|
|
||
|
|
[RFC 7159](http://rfc7159.net/rfc7159) describes numbers as follows:
|
||
|
|
> The representation of numbers is similar to that used in most
|
||
|
|
> programming languages. A number is represented in base 10 using decimal
|
||
|
|
> digits. It contains an integer component that may be prefixed with an
|
||
|
|
> optional minus sign, which may be followed by a fraction part and/or an
|
||
|
|
> exponent part. Leading zeros are not allowed. (...) Numeric values that
|
||
|
|
> cannot be represented in the grammar below (such as Infinity and NaN)
|
||
|
|
> are not permitted.
|
||
|
|
|
||
|
|
This description includes both integer and floating-point numbers.
|
||
|
|
However, C++ allows more precise storage if it is known whether the number
|
||
|
|
is a signed integer, an unsigned integer or a floating-point number.
|
||
|
|
Therefore, three different types, [`number_integer_t`](number_integer_t.md),
|
||
|
|
`number_unsigned_t` and [`number_float_t`](number_float_t.md) are used.
|
||
|
|
|
||
|
|
To store unsigned integer numbers in C++, a type is defined by the
|
||
|
|
template parameter `NumberUnsignedType` which chooses the type to use.
|
||
|
|
|
||
|
|
## Notes
|
||
|
|
|
||
|
|
#### Default type
|
||
|
|
|
||
|
|
With the default values for `NumberUnsignedType` (`std::uint64_t`), the
|
||
|
|
default value for `number_unsigned_t` is:
|
||
|
|
|
||
|
|
```cpp
|
||
|
|
std::uint64_t
|
||
|
|
```
|
||
|
|
|
||
|
|
#### Default behavior
|
||
|
|
|
||
|
|
- The restrictions about leading zeros is not enforced in C++. Instead,
|
||
|
|
leading zeros in integer literals lead to an interpretation as octal
|
||
|
|
number. Internally, the value will be stored as decimal number. For
|
||
|
|
instance, the C++ integer literal `010` will be serialized to `8`.
|
||
|
|
During deserialization, leading zeros yield an error.
|
||
|
|
- Not-a-number (NaN) values will be serialized to `null`.
|
||
|
|
|
||
|
|
#### Limits
|
||
|
|
|
||
|
|
[RFC 7159](http://rfc7159.net/rfc7159) specifies:
|
||
|
|
> An implementation may set limits on the range and precision of numbers.
|
||
|
|
|
||
|
|
When the default type is used, the maximal integer number that can be
|
||
|
|
stored is `18446744073709551615` (UINT64_MAX) and the minimal integer
|
||
|
|
number that can be stored is `0`. Integer numbers that are out of range
|
||
|
|
will yield over/underflow when used in a constructor. During
|
||
|
|
deserialization, too large or small integer numbers will be automatically
|
||
|
|
be stored as [`number_integer_t`](number_integer_t.md) or
|
||
|
|
[`number_float_t`](number_float_t.md).
|
||
|
|
|
||
|
|
[RFC 7159](http://rfc7159.net/rfc7159) further states:
|
||
|
|
> Note that when such software is used, numbers that are integers and are
|
||
|
|
> in the range \f$[-2^{53}+1, 2^{53}-1]\f$ are interoperable in the sense
|
||
|
|
> that implementations will agree exactly on their numeric values.
|
||
|
|
|
||
|
|
As this range is a subrange (when considered in conjunction with the
|
||
|
|
number_integer_t type) of the exactly supported range [0, UINT64_MAX],
|
||
|
|
this class's integer type is interoperable.
|
||
|
|
|
||
|
|
#### Storage
|
||
|
|
|
||
|
|
Integer number values are stored directly inside a `basic_json` type.
|
||
|
|
|
||
|
|
## Version history
|
||
|
|
|
||
|
|
- Added in version 2.0.0.
|