Signed Integer Number Generators (int_, etc.)

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##### Signed Integer Number Generators (`int_`, etc.)

###### Description

The `int_generator` can generate signed integers of arbitrary length and size. This is almost the same as the `uint_generator`. The only difference is the additional task of generating the `'+'` or `'-'` sign preceding the number. The class interface is the same as that of the `uint_generator`.

The `int_generator` generator can be used to emit ordinary primitive C/C++ integers or even user defined scalars such as bigints (unlimited precision integers) if the type follows certain expression requirements (for more information about the requirements, see below).

###### Header

    // forwards to <boost/spirit/home/karma/numeric/int.hpp>
    #include <boost/spirit/include/karma_int.hpp>

Also, see Include Structure.

###### Namespace

Name
`boost::spirit::lit // alias: boost::spirit::karma::lit`
`boost::spirit::short_ // alias: boost::spirit::karma::short_`
`boost::spirit::int_ // alias: boost::spirit::karma::int_`
`boost::spirit::long_ // alias: boost::spirit::karma::long_`
`boost::spirit::long_long // alias: boost::spirit::karma::long_long`

| Note
The generators `long_long` and `long_long(num)` are only available on platforms where the preprocessor constant `BOOST_HAS_LONG_LONG` is defined (i.e. on platforms having native support for `long long` (64 bit) integer types).

| Note
`lit` is reused by the String Generators, the Character Generators, and the Numeric Generators. In general, a char generator is created when you pass in a character, a string generator is created when you pass in a string, and a numeric generator is created when you use a numeric literal.

###### Synopsis

    template <
        typename T
      , unsigned Radix
      , bool force_sign>
    struct int_generator;

###### Template parameters

Parameter | Description | Default
--- | --- | ---
`T` | The numeric base type of the numeric parser. | `int`
`Radix` | The radix base. This can be either 2: binary, 8: octal, 10: decimal and 16: hexadecimal. | `10`
`force_sign` | If `true`, all numbers will have a sign (space for zero) | `false`

###### Model of

> `PrimitiveGenerator`

Notation

`num`

  Numeric literal, any signed integer value, or a Lazy Argument that evaluates to a signed integer value of type `Num`

`Num`

  Type of `num`: any signed integer type

`Radix`

  A constant integer literal specifying the required radix for the output conversion. Valid values are `2`, `8`, `10`, and `16`.

`force_sign`

  A constant boolean literal specifying whether the generated number should always have a sign (`'+'` for positive numbers, `'-'` for negative numbers and a '`` ' for zero).

###### Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in `PrimitiveGenerator`.

Expression | Semantics
--- | ---
`lit(num)` | Generate the integer literal `num` using the default formatting (radix is `10`, sign is only printed for negative literals). This generator never fails (unless the underlying output stream reports an error).
    short_
    int_
    long_
    long_long
| Generate the integer provided by a mandatory attribute using the default formatting (radix is `10`, sign is only printed for negative literals). This generator never fails (unless the underlying output stream reports an error).
    short_(num)
    int_(num)
    long_(num)
    long_long(num)
| Generate the integer provided by the immediate literal value the generator is initialized from using the default formatting (radix is `10`, sign is only printed for negative literals). If this generator has an associated attribute it succeeds only if the attribute is equal to the immediate literal (unless the underlying output stream reports an error). Otherwise this generator fails and does not generate any output.

All generators listed in the table above (except `lit(num)`) are predefined specializations of the `int_generator<Num, Radix, force_sign>` basic integer number generator type described below. It is possible to directly use this type to create integer generators using a wide range of formatting options.

Expression | Semantics
--- | ---
    int_generator<
        Num, Radix, force_sign
    >()
| Generate the integer of type `Num` provided by a mandatory attribute using the specified `Radix` (possible values are `2`, `8`, `10`, and `16`, the default value is `10`). If `force_sign` is `false` (the default), a sign is only printed for negative literals. If `force_sign` is `true`, all numbers will be printed using a sign, i.e. `'-'` for negative numbers, `'+'` for positive numbers, and `' '` for zeros. This generator never fails (unless the underlying output stream reports an error).
    int_generator<
        Num, Radix, force_sign
    >()(num)
| Generate the integer of type `Num` provided by the immediate literal value the generator is initialized from, using the specified `Radix` (possible values are `2`, `8`, `10`, and `16`, the default value is `10`). If `force_sign` is `false` (the default), a sign is only printed for negative literals. If `force_sign` is `true`, all numbers will be printed using a sign, i.e. `'-'` for negative numbers, `'+'` for positive numbers, and `' '` for zeros. If this generator has an associated attribute it succeeds only if the attribute is equal to the immediate literal (unless the underlying output stream reports an error). Otherwise this generator fails and does not generate any output.

###### Additional Requirements

The following lists enumerate the requirements which must be met in order to use a certain type `Num` to instantiate and use a `int_generator<Num, Radix, force_sign>`.

If `boost::is_integral<Num>::value` is `true` the type `Num` must have defined:

- comparison operators for: `<`, `<=`, `==`, `!=`, `>`, and `>=`
- numeric operators for: `+`, `-`, `/`, `*`, `%`, and unary `-`

If `boost::is_integral<Num>::value` is `false` the type `Num` must have defined:

- comparison operators for: `<`, `<=`, `==`, `!=`, `>`, and `>=`
- numeric operators for: `+`, `-`, `/`, `*`, `%`, and unary `-`
- helper functions implementing the interface and the semantics of: `std::fmod`, `std::fabs`, `std::pow`, `std::lround`, `std::ltrunc`, `std::floor`, and `std::ceil`. These need to be defined in a way so that they will be found using argument dependent lookup (ADL).

###### Attributes

Expression | Attribute
--- | ---
`lit(num)` | `unused`
`short_` | `short`, attribute is mandatory (otherwise compilation will fail)
`short_(num)` | `short`, attribute is optional, if it is supplied, the generator compares the attribute with `num` and succeeds only if both are equal, failing otherwise.
`int_` | `int`, attribute is mandatory (otherwise compilation will fail)
`int_(num)` | `int`, attribute is optional, if it is supplied, the generator compares the attribute with `num` and succeeds only if both are equal, failing otherwise.
`long_` | `long`, attribute is mandatory (otherwise compilation will fail)
`long_(num)` | `long`, attribute is optional, if it is supplied, the generator compares the attribute with `num` and succeeds only if both are equal, failing otherwise.
`long_long` | `long long`, attribute is mandatory (otherwise compilation will fail)
`long_long(num)` | `long long`, attribute is optional, if it is supplied, the generator compares the attribute with `num` and succeeds only if both are equal, failing otherwise.
    int_generator<
        Num, Radix, force_sign
    >()
| `Num`, attribute is mandatory (otherwise compilation will fail)
    int_generator<
        Num, Radix, force_sign
    >()(num)
| `Num`, attribute is optional, if it is supplied, the generator compares the attribute with `num` and succeeds only if both are equal, failing otherwise.

| Note
In addition to their usual attribute of type `Num` all listed generators accept an instance of a `boost::optional<Num>` as well. If the `boost::optional<>` is initialized (holds a value) the generators behave as if their attribute was an instance of `Num` and emit the value stored in the `boost::optional<>`. Otherwise the generators will fail.

###### Complexity

> O(N), where `N` is the number of digits needed to represent the generated integer number

###### Example

| Note
The test harness for the example(s) below is presented in the Basics Examples section.

Some includes:

    #include <boost/spirit/include/karma.hpp>
    #include <boost/spirit/include/support_utree.hpp>
    #include <boost/spirit/include/phoenix_core.hpp>
    #include <boost/spirit/include/phoenix_operator.hpp>
    #include <boost/fusion/include/std_pair.hpp>
    #include <iostream>
    #include <string>

Some using declarations:

    using boost::spirit::karma::int_;
    using boost::spirit::karma::lit;

Basic usage of an `int_` generator:

    test_generator("-2", lit(-2));
    test_generator("-2", int_(-2));
    test_generator_attr("-2", int_(-2), -2);
    test_generator_attr("", int_(-2), 3);    // fails (as -2 != 3)!
    test_generator_attr("-2", int_, -2);