Units From Strings¶

The units library contains a few functions to generate various types from string representations

precise_unit unit_from_string(const std::string& ustring, std::uint32_t flags=0) : will generate a precise_unit based on the data in the string
unit unit_cast_from_string(const std::string& ustring, std::uint32_t flags=0): will generate a unit based on the data in the string
precise_measurement measurement_from_string(const std::string& ustring, std::uint32_t flags=0): will generate a precise_measurement from the data in the string
measurement measurement_cast_from_string(const std::string& ustring, std::uint32_t flags=0): will generate a measurement from the data in the string
uncertain_measurement uncertain_measurement_from_string(const std::string& ustring, std::uint32_t flags=0): will generate an uncertain_measurement from the data in the string

The general form is to take a string and optionally a flag object. See Conversion Flags for a detailed description of the flags. Generally it is fine to leave off the flag argument.

Unit Strings¶

in general the unit string conversion is intended to be as flexible as possible. just about any unit normally written can be converted.

For example

“m/s”
“meter/second”
“meter/s”
“metre/s”
“meters/s”
“meters per second”
“metres per second”
“m per sec”
“meterpersecond”
“METERS/s”
“m*s^-1”
“meters*seconds^(-1)”
“(second/meter)^(-1)”
“100 centimeters / 1000 ms”

Will all produce the unit of meters per second. As a note there are quite a few more units that can be converted from strings than are listed in the Defined Units. Numbers are supported and become part of the unit. “99 feet” would create a new unit with a definition of 99 ft. The multiplier stored would include the conversion from meters to feet*99. This allows for arbitrary unit definitions. The + operator also works if the units on both sides have the same base for example 3 ft + 2 in would be the equivalent of 38 inches. If the units do not have the same base + is interpreted as a multiplication.

Measurement strings¶

The conversion from a string to measurement looks for a leading number before the unit. The “99 feet” in the previous example would then get a measurement value of 99 and the unit would be feet. The measurement from string function also can interpret written numbers such as “three thousand four hundred and twenty-seven miles” This should get correctly read as 3427 miles.

The conversion function also handles a few cases where the unit symbol is written before the value such as currency $27.92 would be a value of 27.92 with the currency unit.

Uncertain Measurements¶

Similarly to Measurement strings, uncertain measurements can also be converted from strings see Uncertain Measurements for additional details on the formats supported.