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api/basic_json/number_integer_t.md

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+# <small>nlohmann::basic_json::</small>number_integer_t
+
+```cpp
+using number_integer_t = NumberIntegerType;
+```
+
+The type used to store JSON numbers (integers).
+
+[RFC 8259](https://tools.ietf.org/html/rfc8259) 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_unsigned_t`](number_unsigned_t.md) and [`number_float_t`](number_float_t.md) are
+used.
+
+To store integer numbers in C++, a type is defined by the template parameter `NumberIntegerType` which chooses the type
+to use.
+
+## Notes
+
+#### Default type
+
+With the default values for `NumberIntegerType` (`std::int64_t`), the default value for `number_integer_t` is
+`#!cpp std::int64_t`.
+
+#### Default behavior
+
+- The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in integer literals lead to an
+  interpretation as an octal number. Internally, the value will be stored as a decimal number. For instance, the C++
+  integer literal `010` will be serialized to `8`. During deserialization, leading zeros yield an error.
+
+#### Limits
+
+[RFC 8259](https://tools.ietf.org/html/rfc8259) 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 `9223372036854775807` (INT64_MAX) and
+the minimal integer number that can be stored is `-9223372036854775808` (INT64_MIN). 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 automatically be stored as [`number_unsigned_t`](number_unsigned_t.md) or [`number_float_t`](number_float_t.md).
+
+[RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
+> Note that when such software is used, numbers that are integers and are in the range $[-2^{53}+1, 2^{53}-1]$ are
+> interoperable in the sense that implementations will agree exactly on their numeric values.
+
+As this range is a subrange of the exactly supported range [INT64_MIN, INT64_MAX], this class's integer type is
+interoperable.
+
+#### Storage
+
+Integer number values are stored directly inside a `basic_json` type.
+
+## Examples
+
+??? example
+
+    The following code shows that `number_integer_t` is by default, a typedef to `#!cpp std::int64_t`.
+     
+    ```cpp
+    --8<-- "examples/number_integer_t.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/number_integer_t.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.