Class convert_units (o2scl)¶
-
template<class
fp_t
= double>
classo2scl
::
convert_units
¶ Convert units.
Allow the user to convert between two different units after specifying a conversion factor. This class will also automatically combine two conversion factors to create a new unit conversion (but it cannot combine more than two).
Conversions are performed by the convert() function. The run-time unit cache is initially filled with hard-coded conversions, and convert() searches this cache is searched for the requested conversion first. If the conversion is not found and if use_gnu_units is true, then convert() tries to open a pipe to open a shell to get the conversion factor from
'units'
. If this is successful, then the conversion factor is returned and the conversion is added to the cache.If the GNU units command is not in the local path, the user may modify units_cmd_string to specify the full pathname. One can also modify units_cmd_string to specify a different
units.dat
file.Example:
convert_units cu; cout << "A solar mass is " << cu.convert("Msun","g",1.0) << " g. " << endl;
An object of this type is created by o2scl_settings (of type lib_settings_class) for several unit conversions used internally in .
- Idea for Future:
Add G=1.
- Note
Combining two conversions allows for some surprising apparent contradictions from numerical precision errors. If there are two matching unit conversion pairs which give the same requested conversion factor, then one can arrange a situation where the same conversion factor is reported with slightly different values after adding a related conversion to the table. One way to fix this is to force the class not to combine two conversions by setting combine_two_conv to false. Alternatively, one can ensure that no combination is necessary by manually adding the desired combination conversion to the cache after it is first computed.
- Note
uses some unit aliases which are not used the the GNU or OSX units commands, like “Msun” for the solar mass and adds some units not present like “Rschwarz” for the Schwarzchild radius of a 1 solar mass black hole.
- Note
Only the const versions, convert_const and convert_ret_const are guaranteed to be thread-safe, since they are not allowed to update the unit cache.
- Idea for Future:
An in_cache() function to test to see if a conversion is currently in the cache.
Flags for natural units
-
bool
c_is_1
¶
-
bool
hbar_is_1
¶
-
bool
kb_is_1
¶
-
bool
G_is_1
¶
-
void
set_vars
(fp_t m, fp_t k, fp_t s, fp_t K, fp_t A, fp_t mol, fp_t cd, std::map<std::string, fp_t> &vars, bool test_vars = false) const¶ Set variables for the calculator object for convert_calc()
-
int
convert_internal
(std::string from, std::string to, fp_t val, fp_t &converted, fp_t &factor, bool &new_conv) const¶ The internal conversion function which tries the cache first and, if that failed, tries GNU units.
This function returns 0 if the conversion was successful. If the conversion fails and err_on_fail is
true
, then the error handler is called. If the conversion fails and err_on_fail isfalse
, then the value o2scl::exc_enotfound is returned.The public conversion functions in this class are basically just wrappers around this internal function.
-
int
convert_gnu_units
(std::string from, std::string to, fp_t val, fp_t &converted, fp_t &factor) const¶ Attempt to use GNU units to perform a conversion.
This function attempts to open a pipe to GNU units independent of the value of use_gnu_units. However, it will always return a non-zero value if
HAVE_POPEN
is not defined signaling that thepopen()
function is not available (but does not call the error handler in this case). The function returns 0 if the conversion was successful. If HAVE_POPEN is defined but the call to GNU units fails for some reason, then the error handler is called if err_on_fail is true.- Idea for Future:
Finer control on verbose=1 vs. verbose=2
-
int
convert_cache
(std::string from, std::string to, fp_t val, fp_t &converted, fp_t &factor) const¶ Attempt to construct a conversion from the internal unit cache.
This function returns 0 if the conversion was successful and o2scl::exc_efailed otherwise. This function does not call the error handler.
-
convert_units
()¶ Create a unit-conversion object.
-
~convert_units
()¶
-
void
set_natural_units
(bool c_is_one = true, bool hbar_is_one = true, bool kb_is_one = true)¶ Set natural units.
-
void
test_unique
()¶ Test to make sure all units are unique.
-
void
print_units
(std::ostream &out)¶ Print the units in the data base.
-
int
convert_calc
(std::string from, std::string to, fp_t val, fp_t &converted, fp_t &factor) const¶ Automatic unit conversion between SI-based units with a o2scl::calculator object.
Basic usage
User settings
-
int
verbose
¶ Verbosity (default 0)
-
bool
use_gnu_units
¶ If true, use a system call to units to derive new conversions (default true)
This also requires
popen()
.
-
bool
err_on_fail
¶ If true, throw an exception when a conversion fails (default true)
-
bool
combine_two_conv
¶ If true, allow combinations of two conversions (default true)
-
std::string
units_cmd_string
¶ Command string to call units (default “units”)
Conversions which don’t throw exceptions
Manipulate cache and create units.dat files
-
void
insert_cache
(std::string from, std::string to, fp_t conv)¶ Manually insert a unit conversion into the cache.
-
void
print_cache
() const¶ Print the present unit cache to std::cout.
-
void
test_cache_calc
() const¶ Desc.
-
void
remove_cache
(std::string from, std::string to)¶ Manually remove a unit conversion into the cache.
-
void
default_conversions
()¶ Add default conversions.
Where possible, this uses templates from constants.h to define the conversions exactly in the user-specified floating-point type.
-
void
make_units_dat
(std::string fname, bool c_1 = false, bool hbar_1 = false, bool K_1 = false) const¶ Make a GNU
units.dat
file from the GSL constants.If
c_1
is true, then the second is defined in terms of meters so that the speed of light is unitless. Ifhbar_1
is true, then the kilogram is defined in terms ofs/m^2
so that \( \hbar \) is unitless.- Note
While convert() generally works with the OSX version of ‘units’, the OSX version can’t read units.dat files created by this function.
- Note
Not all of the GSL constants or the canonical GNU units conversions are given here.
-
int
test_cache
()¶ Exhaustive test the cache against GNU units.
Protected Types
-
typedef std::map<std::string, unit_t, std::greater<std::string>>::iterator
miter
¶ The iterator type.
-
typedef std::map<std::string, unit_t, std::greater<std::string>>::const_iterator
mciter
¶ The const iterator type.
-
typedef struct o2scl::convert_units::der_unit_s
der_unit
¶ Type of a derived unit.
Protected Attributes
-
std::map<std::string, unit_t, std::greater<std::string>>
mcache
¶ The cache where unit conversions are stored.
-
std::vector<std::string>
prefixes
¶ SI prefix labels.
Protected Static Attributes
-
const size_t
n_prefixes
= 24¶ Number of SI prefixes.
-
struct
der_unit_s
¶ Type of a derived unit.
-
struct
unit_t
¶ The type for caching unit conversions.