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Data in astronomy can have many types, numeric (numbers) and strings (names, identifiers). The former can also be divided into integers and floats, see Numeric data types for a thorough discussion of the different numeric data types and which one is useful for different contexts.
To deal with the very large diversity of types that are available (and used
in different contexts), in Gnuastro each type is identified with global
integer variable with a fixed name, this variable is then passed onto
functions that can work on any type or is stored in Gnuastro’s Generic data container (gal_data_t) as one piece of meta-data.
The actual values within these integer constants is irrelevant and you
should never rely on them. When you need to check, explicitly use the named
variable in the table below. If you want to check with more than one type,
you can use C’s switch statement.
Since Gnuastro heavily deals with file input-output, the types it defines
are fixed width types, these types are portable to all systems and are
defined in the standard C header stdint.h. You don’t need to include
this header, it is included by any Gnuastro header that deals with the
different types. However, the most commonly used types in a C (or C++)
program (for example int or long) are not defined by their
exact width (storage size), but by their minimum storage. So for example on
some systems, int may be 2 bytes (16-bits, the minimum required by
the standard) and on others it may be 4 bytes (32-bits, common in modern
systems).
With every type, a unique “blank” value (or place holder showing the absence of data) can be defined. Please see Library blank values (blank.h) for constants that Gnuastro recognizes as a blank value for each type. See Numeric data types for more explanation on the limits and particular aspects of each type.
This is just a place holder to specifically mark that no type has been set.
Identifier for a bit-stream. Currently no program in Gnuastro works directly on bits, but features will be added in the future.
Identifier for an unsigned, 8-bit integer type: uint8_t (from
stdint.h), or an unsigned char in most modern systems.
Identifier for a signed, 8-bit integer type: int8_t (from
stdint.h), or an signed char in most modern systems.
Identifier for an unsigned, 16-bit integer type: uint16_t (from
stdint.h), or an unsigned short in most modern systems.
Identifier for a signed, 16-bit integer type: int16_t (from
stdint.h), or a short in most modern systems.
Identifier for an unsigned, 32-bit integer type: uint32_t (from
stdint.h), or an unsigned int in most modern systems.
Identifier for a signed, 32-bit integer type: int32_t (from
stdint.h), or an int in most modern systems.
Identifier for an unsigned, 64-bit integer type: uint64_t (from
stdint.h), or an unsigned long in most modern 64-bit systems.
Identifier for a signed, 64-bit integer type: int64_t (from
stdint.h), or an long in most modern 64-bit systems.
Identifier for a int type. This is just an alias to int16, or
int32 types, depending on the system.
Identifier for a unsigned int type. This is just an alias to
uint16, or uint32 types, depending on the system.
Identifier for a unsigned long type. This is just an alias to
uint32, or uint64 types for 32-bit, or 64-bit systems
respectively.
Identifier for a long type. This is just an alias to int32,
or int64 types for 32-bit, or 64-bit systems respectively.
Identifier for a size_t type. This is just an alias to
uint32, or uint64 types for 32-bit, or 64-bit systems
respectively.
Identifier for a 32-bit single precision floating point type or
float in C.
Identifier for a 64-bit double precision floating point type or
double in C.
Identifier for a complex number composed of two float types. Note
that the complex type is not yet fully implemented in all Gnuastro’s
programs.
Identifier for a complex number composed of two double types. Note
that the complex type is not yet fully implemented in all Gnuastro’s
programs.
Identifier for a string of characters (char *).
Identifier for a linked list of string of characters
(gal_list_str_t, see List of strings).
The functions below are defined to make working with the integer constants
above easier. In the functions below, the constants above can be used for
the type input argument.
type)Return the number of bytes occupied by type. Internally, this
function uses C’s sizeof operator to measure the size of each type.
type, int long_name)Return a string literal that contains the name of type. It can
return both short and long formats of the type names (for example
f32 and float32). If long_name is non-zero, the long
format will be returned, otherwise the short name will be returned. The
output string is statically allocated, so it should not be freed. This
function is the inverse of the gal_type_from_name function. For the
full list of names/strings that this function will return, see Numeric data types.
*str)Return the Gnuastro integer constant that corresponds to the string
str. This function is the inverse of the gal_type_name
function and accepts both the short and long formats of each type. For the
full list of names/strings that this function will return, see Numeric data types.
type, void *in)Put the minimum possible value of type in the space pointed to by
in. Since the value can have any type, this function doesn’t return
anything, it assumes the space for the given type is available to in
and writes the value there. Here is one example
int32_t min; gal_type_min(GAL_TYPE_INT32, &min);
Note: Do not use the minimum value for a blank value of a general (initially unknown) type, please use the constants/functions provided in Library blank values (blank.h) for the definition and usage of blank values.
type, void *in)Put the maximum possible value of type in the space pointed to by
in. Since the value can have any type, this function doesn’t return
anything, it assumes the space for the given type is available to in
and writes the value there. Here is one example
uint16_t max; gal_type_max(GAL_TYPE_INT16, &max);
Note: Do not use the maximum value for a blank value of a general (initially unknown) type, please use the constants/functions provided in Library blank values (blank.h) for the definition and usage of blank values.
type)Return 1 if the type is an integer (any width and any sign).
type)Return 1 if the type is a linked list and zero otherwise.
first_type, int second_type)Return the larger of the two given types which can be used for the type of the output of an operation involving the two input types.
*in, size_t size)Return the bit-string in the size bytes that in points
to. The string is dynamically allocated and must be freed afterwards. You
can use it to inspect the bits within one region of memory. Here is one
short example:
int32_t a=2017;
char *bitstr=gal_type_bit_string(&a, 4);
printf("%d: %s (%X)\n", a, bitstr, a);
free(bitstr);
which will produce:
2017: 11100001000001110000000000000000 (7E1)
As the example above shows, the bit-string is not the most efficient way to
inspect bits. If you are familiar with hexadecimal notation, it is much
more compact, see https://en.wikipedia.org/wiki/Hexadecimal. You can
use printf’s %x or %X to print integers in hexadecimal
format.
*ptr, uint8_t type, int quote_if_str_has_space);Read the contents of the memory that ptr points to (assuming it has
type type and print it into an allocated string which is returned.
If the memory is a string of characters and quote_if_str_has_space
is non-zero, the output string will have double-quotes around it if it
contains space characters. Also, note that in this case, ptr must be
a pointer to an array of characters (or char **), as in the example
below (which will put "sample string" into out):
char *out, *string="sample string" out = gal_type_to_string(&string, GAL_TYPE_STRING, 1);
**out, char *string, uint8_t type)Read a string as a given data type and put a pointer to it in
*out. When *out!=NULL, then it is assumed to be already
allocated and the value will be simply put there. If *out==NULL,
then space will be allocated for the given type and the string will be read
into that type.
Note that when we are dealing with a string type, *out should be
interpreted as char ** (one element in an array of pointers to
different strings). In other words, out should be char ***.
This function can be used to fill in arrays of numbers from strings (in an
already allocated data structure), or add nodes to a linked list (if the
type is a list type). For an array, you have to pass the pointer to the
ith element where you want the value to be stored, for example
&(array[i]).
If the string was successfully parsed to the requested type, this function
will return a 0 (zero), otherwise it will return 1
(one). This output format will help you check the status of the conversion
in a code like the example below:
if( gal_type_from_string(&out, string, GAL_TYPE_FLOAT32) )
{
fprintf(stderr, "%s couldn't be read as float32.\n", string);
exit(EXIT_FAILURE);
}
*string, uint8_t *type)Read string into smallest type that can host the number, the allocated space for the number will be returned and the type of the number will be put into the memory that type points to.
If string couldn’t be read as a number, this function will return NULL.
This function calls the C library’s strtod function to read string as a double-precision floating point number.
When successful, it will check the value to put it in the smallest numerical data type that can handle it.
However, if string is successfully parsed as a number and there is . in string, it will force the number into floating point types.
For example "5" is read as an integer, while "5." or "5.0", or "5.00" will be read as a floating point (single-precision).
For the ranges acceptable by each type see Numeric data types. For integers, the range is clear, but for floating point types, this function will count the number of significant digits and determine if the given string is single or double precision as described in that section.
Next: Pointers, Previous: Multithreaded programming, Up: Gnuastro library [Contents][Index]
GNU Astronomy Utilities 0.15 manual, May 2021.