TCX Unit Conversion Library

Sample Image - TcxUnitConverter.gif

This library offers functions to convert values between units of measurement. It's very simple to use. For example, to convert between mph (miles per hour) to m/s (meters per second), just use the following code:

double dValue = 1.0;
TcxConvertUnit( dValue, _T("mph"), _T("m/s") );
// <dValue> is now in "m/s"

The units are represented as strings, as the intention of the library is to afford unit entrance support at the UI level. In fact, the Demo Application that accompanies this article is a very simple (yet powerful) unit conversion utility.

The table of supported units is currently hard coded. You can add your own new units just following the instructions in the source file (TcxUnitConverter.cpp).

The unit interpreter accepts all the multiplication prefixes of the International System of Units (see the Appendices section).

The unit interpreter accepts also linear unit expressions. For example, you can convert from acre (Acres) to mi^2 (square miles), or from N (Newtons, the unit of strength in the International System of Units) to m*kg/s^2 (meter times kilogram per square second).

The following are samples of valid unit expressions (they are all units of strength).

m*kg/s^2

m*kg*s^-2

m/kg^-1*s*s

kg*s^-2/m^-1

There can be only one division ('/') symbol in the expression, and all right terms are considered as part of the denominator (e.g. m/s^2 equals m/s*s). Parenthesis are not used. Exponents, when applicable, must be positive or negative literal integers.

This source code is provided "as is" without express or implied warranty.
Use it at your own risk!
While I have made every effort to remove any undesirable "bugs", I cannot be held responsible if it causes any damage or loss of time, data, or Martian probes.

Known Limitations

The unit converter can only perform the following type of conversion:

    Unit1 = K * Unit2;  // K is a floating point constant

This is valid for the greatest multitude of the common day units we can think of, but for temperature units.

Temperature units as Kelvin, Celsius and Fahrenheits all demand conversion formulas in the following form:

    Unit1 = K * Unit2 + K0;  // K and K0 are floating point constants

The library will still convert between these units, but, in this case, the value is supposed to be a temperature variation rather than an absolute temperature.

Things to do

Implement UI Controls that automatically make use of these features.

Implement a more flexible Unit Converter so sets of units can be "loaded" and combined in runtime.

Buy a Ferrari.

Using the Demo Application

In the From/Value field, enter the source value you want to convert. In the From/Unit field, type the unit of the source value, or choose one from the dropdown list. In the To/Unit field, type the target unit or choose one from the dropdown list. The result will be displayed in the To/Result just-in-time. You can select & copy from this field.

To enter unit expression in either the From/Unit or the To/Unit fields, you must type them. The dropdown lists show only sigle units.

Appendices

Table 1: Multiplication prefixes of the International System of Units

Prefix	Name	Constant
Y	Yotta	1e+24
Z	Zetta	1e+21
E	Exa	1e+18
P	Peta	1e+15
T	Tera	1e+12
G	Giga	1e+9
M	Mega	1e+6
k or K	kilo	1e+3
h or H	hecto	1e+2
D	Deka	1e+1
d	deci	1e-1
c	cent	1e-2
m	mili	1e-3
u or µ	micro	1e-6
n	nano	1e-9
p	pico	1e-12
f	femto	1e-15
a	atto	1e-18
z	zepto	1e-21
y	yocto	1e-24

Table 2: Basic Units

Abbr	Tag
A	Ampere
K	Kelvin
cd	Candela
g	Gram
m	Meter
mol	Mole
r	Radian
s	Second
sr	Steradian

Table 3: Derived Units

Abbr	Tag	Definition
Bq	becquerel	1 [l/s]
Btu	InternationalTableBtu	1055.05585262 [Kg*m^2/s^2]
C	Coulomb	1 [A*s]
Ci	Curie	3.7*1010 [l/s]
F	Farad	1 [A^2s^4/Kgm^2]
Fdy	Faraday	96487 [A*s]
Gy	Gray	1 [m^2/s^2]
H	Henry	1 [Kgm^2/A^2s^2]
Hz	Hertz	1 [s^-1]
J	Joule	1 [Kg*m^2/s^2]
Knot	NauticalMilesPerHour	463.0/900.0 [m/s]
N	Newton	1 [Kg*m/s^2]
Ohm	Ohm	1 [Kgm^2/A^2s^3]
OzUK	UKFluidOunce	2.8413075e-5 [m^3]
P	Poise	0.1 [Kg/m*s]
Pa	Pascal	1 [Kg/m*s]
Pdl	Poundal	0.13825495376 [Kg*m/s^2]
Pica	Pica	1.0/72.0 [in]
R	Roentgen	0.000258 [A*s/Kg]
S	Siemens	1 [A^2s^3/Kgm^2]
St	Stokes	0.0001 [m^2/s]
Sv	Sievert	1 [m^2/s^2]
T	Tesla	1 [Kg/A*s^2]
U	UnifiedAtomicMass	1.6605402e-27 [Kg]
V	Volt	1 [Kgm^2/As^2]
W	Watt	1 [Kg*m^2/s^3]
Wb	Weber	1 [Kgm^2/As^2]
acre	Acre	4046.87260987 [m^2]
arcmin	ArcMinute	2.9088820866e-4 [r]
arcs	ArcSecond	4.848136111e-6 [r]
atm	Attmosphere	101325 [Kg/m*s^2]
au	AstronomicalUnit	1.495979*1011 [m]
b	Barn	1e-28 [m^2]
bar	Bar	100000 [Kg/m*s^2]
bbl	Barrel	0.158987294928 [m^3]
bu	Bushel	0.03523907 [m^3]
c	LightSpeed	299792458 [m/s]
cal	Calorie	4.1868 [Kg*m^2/s^2]
chain	Chain	20.1168402337 [m]
ct	Carat	0.0002 [Kg]
cu	USCup	2.365882365e-4 [m^3]
d	day	86400 [s]
dyn	Dyne	0.00001 [Kg*m/s^2]
eV	ElectronVolt	1.60217733e-19 [Kg*m^2/s^2]
erg	Erg	0.0000001 [Kg*m^2/s^2]
fath	Fathom	1.82880365761 [m]
fbm	BoardFoot	0.002359737216 [m^3]
fc	Footcandle	10.7639104167 [cd*sr/m^2]
fermi	Fermi	1e-15 [m]
flam	Footlambert	3.42625909964 [cd/m^2]
ft	InternationalFoot	0.3048 [m]
ftUS	SurveyFoot	0.304800609601 [m]
ga	StandardFreefall	9.80665 [m/s^2]
gal	USGallon	0.003785411784 [m^3]
galC	CanadianGallon	0.00454609 [m^3]
galUK	UKGallon	0.004546092 [m^3]
gf	GramForce	0.00980665 [Kg*m/s^2]
grad	Grade	1.57079632679e-2 [r]
grain	Grain	0.00006479891 [Kg]
h	Hour	3600 [s]
ha	Hectare	10000 [m^2]
hp	horsepower	745.699871582 [Kg*m^2/s^2]
in	Inch	0.0254 [m]
inH2O	InchesOfWater	248.84 [Kg/m*s^2]
inHg	InchesOfMercury	3386.38815789 [Kg/m*s^2]
kip	KilopoundForce	4448.22161526 [Kg*m/s^2]
kph	KilometersPerHour	5.0/18.0 [m/s]
l	Liter	0.001 [m^3]
lam	Lambert	3183.09886184 [cd/m^2]
lb	AvoirdupoisPound	0.45359267 [Kg]
lbf	PoundForce	4.44822161526 [Kg*m/s^2]
lbt	TroyPound	0.3732417216 [Kg]
lm	Lumen	1 [cd*sr]
lx	Lux	1 [cd*sr/m^2]
lyr	LightYear	9.46052840488*1015 [m]
mho	Mho	1 [A^2s^2/Kgm^2]
mi	InternationalMile	1609.344 [m]
miUS	USStatuteMile	1609.34721869 [m]
mil	Mil	0.0000254 [m]
min	Minute	60 [s]
mmHg	MilimeterOfMercury	133.322368421 [Kg/m*s^2]
mph	MilesPerHour	0.44704 [m/s]
nmi	NauticalMile	1852 [m]
oz	Ounce	0.028349523125 [Kg]
ozfl	USFluidOunce	2.95735295625e-5 [m^3]
ozt	TroyOunce	0.0311034768 [Kg]
pc	Parsec	3.08567818585106 [m]
ph	Phot	10000 [cd*sr/m^2]
pk	Peck	0.0088097675 [m^3]
psi	PoundsPerSquareInch	6894.75729317 [Kg/m*s^2]
pt	Pint	0.000473176473 [m^3]
qt	Quart	0.000946352946 [m^3]
rad	Rad	0.01 [m^2/s^2]
rd	Rod	5.02921005842 [m]
rem	Rem	0.01 [m^2/s^2]
sb	Stilb	10000 [cd/m^2]
slug	Slug	14.5939029372 [Kg]
st	Stere	1 [m^3]
t	MetricTon	1000 [Kg]
tbsp	Tablespoon	1.47867647813e-5 [m^3]
therm	EECTherm	105506000 [Kg*m^2/s^2]
ton	ShortTon	907.18474 [Kg]
tonUK	UKLongTon	1016.0469088 [Kg]
torr	Torr	133.322368421 [Kg/m^2]
tsp	Teaspoon	4.92892159375e-6 [m^3]
yd	InternationalYard	0.9144 [m]
yr	Year	31556925.9747 [s]
°	Degree	1.74532925199e-2 [r]
°C	DegreeCelsius	1.0 [K]
°F	DegreesFahrenheit	1.0/1.8 [K]
°R	DegreesRankine	1.0/1.8 [K]
µ	Micron	1e-6 [m]
Å	Angstrom	1e-10 [m]

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