GwySIUnit: Gwyddion Library Reference Manual

## GwySIUnit GwySIUnit — SI unit representation, physical quantitiy formatting |

## Functions

#define | gwy_si_unit_duplicate()
#define | gwy_si_unit_assign()
GwySIUnit * | gwy_si_unit_new ()
GwySIUnit * | gwy_si_unit_new_parse ()
void | gwy_si_unit_set_from_string ()
void | gwy_si_unit_set_from_string_parse ()
gchar * | gwy_si_unit_get_string ()
GwySIUnit * | gwy_si_unit_multiply ()
GwySIUnit * | gwy_si_unit_divide ()
GwySIUnit * | gwy_si_unit_power ()
GwySIUnit * | gwy_si_unit_nth_root ()
GwySIUnit * | gwy_si_unit_power_multiply ()
GwySIUnit * | gwy_si_unit_factor_to_base ()
gboolean | gwy_si_unit_equal ()
gboolean | gwy_si_unit_equal_string ()
GwySIValueFormat * | gwy_si_unit_get_format ()
GwySIValueFormat * | gwy_si_unit_get_format_for_power10 ()
GwySIValueFormat * | gwy_si_unit_get_format_with_resolution ()
GwySIValueFormat * | gwy_si_unit_get_format_with_digits ()

## Signals

void | value-changed | Run First

## Types and Values

struct | GwySIUnit
struct | GwySIUnitClass

## Object Hierarchy

        GObject
        ╰── GwySIUnit

## Implemented Interfaces

GwySIUnit implements GwySerializable.

## Includes

    #include <libgwyddion/gwyddion.h>

## Description

GwySIUnit object represents a physical SI unit (or any other unit), it can be created from a unit string with `gwy_si_unit_new()`.

GwySIUnit is also responsible for prefixes selection and generally formatting of physical quantities (see also gwymath for pure number formatting functions). There are several functions computing value format (as a GwySIValueFormat structure) with given resolution -- `gwy_si_unit_get_format_with_resolution()`, or number of significant digits -- `gwy_si_unit_get_format_with_digits()`.

## Functions

### gwy_si_unit_duplicate()

    #define             gwy_si_unit_duplicate(siunit)

Convenience macro doing `gwy_serializable_duplicate()` with all the necessary typecasting.

#### Parameters

siunit | An SI unit to duplicate. |

### gwy_si_unit_assign()

    #define             gwy_si_unit_assign(dest, source)

Convenience macro making one SI unit equal to another.

This is just a `gwy_serializable_clone()` wrapper with all the necessary typecasting.

#### Parameters

dest | Target SI unit. |
source | Source SI unit. |

Since: 2.51

### gwy_si_unit_new ()

    GwySIUnit *
    gwy_si_unit_new (const gchar *unit_string);

Creates a new SI unit from string representation.

Unit string represents unit with no prefixes (e. g. "m", "N", "A", etc.)

#### Parameters

unit_string | Unit string (it can be `NULL` for an empty unit). |

#### Returns

A new SI unit.

### gwy_si_unit_new_parse ()

    GwySIUnit *
    gwy_si_unit_new_parse (const gchar *unit_string,
                           gint *power10);

Creates a new SI unit from string representation.

This is a more powerful version of `gwy_si_unit_new()`: `unit_string` may be a relatively complex unit, with prefixes, like "pA/s" or "km^2". Beside conversion to a base SI unit like "A/s" or "m^2" it also computes the power of 10 one has to multiply the base unit with to get an equivalent of `unit_string` .

For example, for `"pA/s"` it will store -12 to `power10` because 1 pA/s is 1e-12 A/s, for `"km^2"` it will store 6 to `power10` because 1 km^2 is 1e6 m^2.

#### Parameters

unit_string | Unit string (it can be `NULL` for an empty unit). |
power10 | Where power of 10 should be stored (or `NULL`). |

#### Returns

A new SI unit.

### gwy_si_unit_set_from_string ()

    void
    gwy_si_unit_set_from_string (GwySIUnit *siunit,
                                 const gchar *unit_string);

Sets string that represents unit.

It must be base unit with no prefixes (e. g. "m", "N", "A", etc.).

#### Parameters

siunit | An SI unit. |
unit_string | Unit string to set `siunit` from (it can be `NULL` for an empty unit). |

### gwy_si_unit_set_from_string_parse ()

    void
    gwy_si_unit_set_from_string_parse (GwySIUnit *siunit,
                                       const gchar *unit_string,
                                       gint *power10);

Changes an SI unit according to string representation.

This is a more powerful version of `gwy_si_unit_set_from_string()`, please see `gwy_si_unit_new_parse()` for some discussion.

#### Parameters

siunit | An SI unit. |
unit_string | Unit string to set `siunit` from (it can be `NULL` for an empty unit). |
power10 | Where power of 10 should be stored (or `NULL`). |

### gwy_si_unit_get_string ()

    gchar *
    gwy_si_unit_get_string (GwySIUnit *siunit,
                            GwySIUnitFormatStyle style);

Obtains string representing a SI unit.

#### Parameters

siunit | An SI unit. |
style | Unit format style. |

#### Returns

A newly allocated string that represents the base unit (with no prefixes).

### gwy_si_unit_multiply ()

    GwySIUnit *
    gwy_si_unit_multiply (GwySIUnit *siunit1,
                          GwySIUnit *siunit2,
                          GwySIUnit *result);

Multiplies two SI units.

#### Parameters

siunit1 | An SI unit. |
siunit2 | An SI unit. |
result | An SI unit to set to product of `siunit1` and `siunit2` . It is safe to pass one of `siunit1` , `siunit2` . It can be `NULL` too, a new SI unit is created then and returned. |

#### Returns

When `result` is `NULL`, a newly created SI unit that has to be dereferenced when no longer used later. Otherwise `result` itself is simply returned, its reference count is NOT increased.

### gwy_si_unit_divide ()

    GwySIUnit *
    gwy_si_unit_divide (GwySIUnit *siunit1,
                        GwySIUnit *siunit2,
                        GwySIUnit *result);

Divides two SI units.

#### Parameters

siunit1 | An SI unit. |
siunit2 | An SI unit. |
result | An SI unit to set to quotient of `siunit1` and `siunit2` . It is safe to pass one of `siunit1` , `siunit2` . It can be `NULL` too, a new SI unit is created then and returned. |

#### Returns

When `result` is `NULL`, a newly created SI unit that has to be dereferenced when no longer used later. Otherwise `result` itself is simply returned, its reference count is NOT increased.

### gwy_si_unit_power ()

    GwySIUnit *
    gwy_si_unit_power (GwySIUnit *siunit,
                       gint power,
                       GwySIUnit *result);

Computes a power of an SI unit.

#### Parameters

siunit | An SI unit. |
power | Power to raise `siunit` to. |
result | An SI unit to set to power of `siunit` . It is safe to pass `siunit` itself. It can be `NULL` too, a new SI unit is created then and returned. |

#### Returns

When `result` is `NULL`, a newly created SI unit that has to be dereferenced when no longer used later. Otherwise `result` itself is simply returned, its reference count is NOT increased.

### gwy_si_unit_nth_root ()

    GwySIUnit *
    gwy_si_unit_nth_root (GwySIUnit *siunit,
                          gint ipower,
                          GwySIUnit *result);

Calulates n-th root of an SI unit.

This operation fails if the result would have fractional powers that are not representable by GwySIUnit.

#### Parameters

siunit | An SI unit. |
ipower | The root to take: 2 means a quadratic root, 3 means cubic root, etc. |
result | An SI unit to set to power of `siunit` . It is safe to pass `siunit` itself. It can be `NULL` too, a new SI unit is created then and returned. |

#### Returns

On success: When `result` is `NULL`, a newly created SI unit that has to be dereferenced when no longer used later, otherwise `result` itself is simply returned, its reference count is NOT increased. On failure `NULL` is always returned.

Since: 2.5

### gwy_si_unit_power_multiply ()

    GwySIUnit *
    gwy_si_unit_power_multiply (GwySIUnit *siunit1,
                                gint power1,
                                GwySIUnit *siunit2,
                                gint power2,
                                GwySIUnit *result);

Computes the product of two SI units raised to arbitrary powers.

This is the most complex SI unit arithmetic function. It can be easily chained when more than two units are to be multiplied.

#### Parameters

siunit1 | An SI unit. |
power1 | Power to raise `siunit1` to. |
siunit2 | An SI unit. |
power2 | Power to raise `siunit2` to. |
result | An SI unit to set to `siunit1` ^`power1` *`siunit2` ^`power2` . It is safe to pass `siunit1` or `siunit2` . It can be `NULL` too, a new SI unit is created then and returned. |

#### Returns

When `result` is `NULL`, a newly created SI unit that has to be dereferenced when no longer used later. Otherwise `result` itself is simply returned, its reference count is NOT increased.

Since: 2.4

### gwy_si_unit_factor_to_base ()

    GwySIUnit *
    gwy_si_unit_factor_to_base (GwySIUnit *siunit,
                                GwySIUnit *result,
                                gdouble *mfactor);

Factors a possibly derived SI unit to base units.

For instance, if `siunit` was set to "N/m" the result will be "kg/s^2".

Normally the result will consist only of the base seven SI units. However, recognised non-SI units (and pseudounits) in `siunit` , such as "px" are left intact in the decomposition.

Also note that the decomposition is done to prefixable units. Kilogram is not prefixable (gram is) and there is no general way to keep the kilo- on the kilograms when deriving units for different powers of 10. Therefore, the calculated factor corresponds to decomposition to grams.

You must multiply the corresponding data with `factor` if you intend to use the `result` for them instead of `unit` !

#### Parameters

siunit | An SI unit. |
result | An SI unit to set to decomposed `siunit` . It is safe to pass `siunit` itself. It can be `NULL` too, a new SI unit is created then and returned. |
mfactor | Location to store multiplicative factor between `siunit` and `result` . For instance, for electronvolt the value 1.60217653e-16 would be stored (the factor 1000 comes from kilogram). Pass `NULL` if you are only interested dimension equality. |

#### Returns

When `result` is `NULL`, a newly created SI unit that has to be dereferenced when no longer used later. Otherwise `result` itself is simply returned, its reference count is NOT increased.

Since: 2.51

### gwy_si_unit_equal ()

    gboolean
    gwy_si_unit_equal (GwySIUnit *siunit,
                       GwySIUnit *siunit2);

Checks whether two SI units are equal.

#### Parameters

siunit | First unit. |
siunit2 | Second unit. |

#### Returns

`TRUE` if the units are equal.

### gwy_si_unit_equal_string ()

    gboolean
    gwy_si_unit_equal_string (GwySIUnit *siunit,
                              const gchar *unit_string);

Checks whether an SI unit corresponds to given string.

Any power-of-ten prefixes are ignored. This function is mostly useful for quick commensurability checks with simple units such as "m" and for checking whether a unit is non-empty (by comparing with `NULL` or an empty string).

#### Parameters

siunit | An SI unit. |
unit_string | Unit string (it can be `NULL` for an empty unit). |

#### Returns

`TRUE` if the units is equivalent to the given string.

Since: 2.49

### gwy_si_unit_get_format ()

    GwySIValueFormat *
    gwy_si_unit_get_format (GwySIUnit *siunit,
                            GwySIUnitFormatStyle style,
                            gdouble value,
                            GwySIValueFormat *format);

Finds a good format for representing a value.

The values should be then printed as value/`format->magnitude` [`format->units` ] with `format->precision` decimal places.

#### Parameters

siunit | An SI unit. |
style | Unit format style. |
value | Value the format should be suitable for. |
format | A value format to set-up, may be `NULL`, a new value format is allocated then. |

#### Returns

The value format. If `format` was `NULL`, a newly allocated format is returned, otherwise (modified) `format` itself is returned.

### gwy_si_unit_get_format_for_power10 ()

    GwySIValueFormat *
    gwy_si_unit_get_format_for_power10 (GwySIUnit *siunit,
                                        GwySIUnitFormatStyle style,
                                        gint power10,
                                        GwySIValueFormat *format);

Finds format for representing a specific power-of-10 multiple of a unit.

The values should be then printed as value/`format->magnitude` [`format->units` ] with `format->precision` decimal places.

This function does not change the precision field of `format` .

#### Parameters

siunit | An SI unit. |
style | Unit format style. |
power10 | Power of 10, in the same sense as `gwy_si_unit_new_parse()` returns it. |
format | A value format to set-up, may be `NULL`, a new value format is allocated then. |

#### Returns

The value format. If `format` was `NULL`, a newly allocated format is returned, otherwise (modified) `format` itself is returned.

### gwy_si_unit_get_format_with_resolution ()

    GwySIValueFormat *
    gwy_si_unit_get_format_with_resolution
                                   (GwySIUnit *siunit,
                                    GwySIUnitFormatStyle style,
                                    gdouble maximum,
                                    gdouble resolution,
                                    GwySIValueFormat *format);

Finds a good format for representing a range of values with given resolution.

The values should be then printed as value/`format->magnitude` [`format->units` ] with `format->precision` decimal places.

#### Parameters

siunit | An SI unit. |
style | Unit format style. |
maximum | The maximum value to be represented. |
resolution | The smallest step (approximately) that should make a visible difference in the representation. |
format | A value format to set-up, may be `NULL`, a new value format is allocated then. |

#### Returns

The value format. If `format` was `NULL`, a newly allocated format is returned, otherwise (modified) `format` itself is returned.

### gwy_si_unit_get_format_with_digits ()

    GwySIValueFormat *
    gwy_si_unit_get_format_with_digits (GwySIUnit *siunit,
                                        GwySIUnitFormatStyle style,
                                        gdouble maximum,
                                        gint sdigits,
                                        GwySIValueFormat *format);

Finds a good format for representing a values with given number of significant digits.

The values should be then printed as value/`format->magnitude` [`format->units` ] with `format->precision` decimal places.

#### Parameters

siunit | An SI unit. |
style | Unit format style. |
maximum | The maximum value to be represented. |
sdigits | The number of significant digits the value should have. |
format | A value format to set-up, may be `NULL`, a new value format is allocated then. |

#### Returns

The value format. If `format` was `NULL`, a newly allocated format is returned, otherwise (modified) `format` itself is returned.

## Types and Values

### struct GwySIUnit

    struct GwySIUnit;

The GwySIUnit struct contains private data only and should be accessed using the functions below.

### struct GwySIUnitClass

    struct GwySIUnitClass {
        GObjectClass parent_class;

        void (*value_changed)(GwySIUnit *siunit);
    };

## Signal Details

### The `“value-changed”` signal

    void
    user_function (GwySIUnit *gwysiunit,
                   gpointer   user_data)

The ::value-changed signal is emitted whenever SI unit changes.

#### Parameters

gwysiunit | The GwySIUnit which received the signal. |
user_data | user data set when the signal handler was connected. |

Flags: Run First