--- name: "gd_constants" section: "3" platform: "linux" package: "libgetdata-doc" version: "0.11.0-15" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/gd_constants" --- # gd\_constants(3) retrieve a list of constant values from a Dirfile ## NAME gd\_constants, gd\_mconstants — retrieve a list of constant values from a Dirfile ## SYNOPSIS **#include \** **const void \*gd\_constants(DIRFILE \****dirfile***, gd\_type\_t** *return\_type***);** **const void \*gd\_mconstants(DIRFILE \****dirfile***, const char** **\****parent***, gd\_type\_t** *return\_type***);** ## DESCRIPTION The **gd\_constants**() function queries a [dirfile(5)](/dirfile/5.md) database specified by *dirfile* and compiles a list of values of the all **CONST** fields defined in the database, excluding meta subfields. The values returned are converted to the data type specified by *return\_type*. The *return\_type* should be one of the following symbols: - **GD\_UINT8**, **GD\_INT8**, **GD\_UINT16**, **GD\_INT16**, **GD\_UINT32**, **GD\_INT32**, **GD\_UINT64,** **GD\_INT64**, **GD\_FLOAT32**, **GD\_FLOAT64**, **GD\_COMPLEX64**, **GD\_COMPLEX128**. See [**gd\_get\_constant**(3)](/gd_get_constant/3.md) for the meaning of these symbols. The *dirfile* argument must point to a valid DIRFILE object previously created by a call to [**gd\_open**(3)](/gd_open/3.md). The **gd\_mconstants**() function returns the same list for **CONST** meta subfields of the parent field specified by *parent*. A corresponding list of names for these fields may be obtained by calling [**gd\_field\_list\_by\_type**(3)](/gd_field_list_by_type/3.md) or [**gd\_mfield\_list\_by\_type**(3)](/gd_mfield_list_by_type/3.md). ## RETURN VALUE Upon successful completion, **gd\_constants**() returns a pointer to an array containing the values of all the constants defined in the dirfile database. Similarly, **gd\_mconstants**() returns a pointer to an array containing the values of the all the meta subfield constants of the specified parent field. The list returned should not be assumed to be in any particular order, although it is guaranteed to be in the same order as the list of **CONST** fields returned by [**gd\_field\_list\_by\_type**(3)](/gd_field_list_by_type/3.md) or [**gd\_mfield\_list\_by\_type**(3)](/gd_mfield_list_by_type/3.md). The array is unterminated. The number of values in the array can be obtained from a call to [**gd\_nfields\_by\_type**(3)](/gd_nfields_by_type/3.md) or [**gd\_nmfields\_by\_type**(3)](/gd_nmfields_by_type/3.md), as appropriate. Memory for the returned array is managed by GetData and should not be de-allocated by the caller. The caller may not modify any values in the array. Doing so may cause database corruption. The pointer returned is guaranteed to be valid only until the function is called again, with the exception that, since each top-level field maintains its own arrays, calling **gd\_mconstants**() for a one parent field does not invalidate the pointer returned for a any other parent. Modifying the dirfile's metadata invalidates any pointer returned by these functions. And no pointers remain valid after the dirfile is de-allocated by a call to [**gd\_close**(3)](/gd_close/3.md) or [**gd\_discard**(3)](/gd_discard/3.md). Once a pointer is invalidated, the caller should not dereference it. If no constants of the appropriate class are defined in the database, NULL is returned. This is not considered an error. On error, these functions return NULL and store a negative-valued error code in the **DIRFILE** object which may be retrieved by a subsequent call to [**gd\_error**(3)](/gd_error/3.md). Possible error codes are:\ .TP 8 **GD\_E\_ALLOC** The library was unable to allocate memory.\ .TP 8 **GD\_E\_BAD\_CODE** The specified *parent* field code was not found, or referred to a metafield (**gd\_mconstants**() only).\ .TP 8 **GD\_E\_BAD\_DIRFILE** The supplied dirfile was invalid.\ .TP 8 **GD\_E\_BAD\_TYPE** The *return\_type* specified was not one of the symbols listed above.\ .TP 8 **GD\_E\_INTERNAL\_ERROR** An internal error occurred in the library while trying to perform the task. This indicates a bug in the library. Please report the incident to the GetData developers. A descriptive error string for the error may be obtained by calling [**gd\_error\_string**(3)](/gd_error_string/3.md). ## HISTORY The functions **get\_constants**() and **get\_mconstants**() appeared in GetData-0.4.0. In GetData-0.7.0, these functions were renamed to **gd\_constants**() and **gd\_mconstants**(). ## SEE ALSO [**gd\_error**(3)](/gd_error/3.md), [**gd\_error\_string**(3)](/gd_error_string/3.md), [**gd\_field\_list\_by\_type**(3)](/gd_field_list_by_type/3.md), [**gd\_get\_constant**(3)](/gd_get_constant/3.md), [**gd\_mfield\_list\_by\_type**(3)](/gd_mfield_list_by_type/3.md), [**gd\_nfields\_by\_type**(3)](/gd_nfields_by_type/3.md), [**gd\_nmfields\_by\_type**(3)](/gd_nmfields_by_type/3.md), [**gd\_open**(3)](/gd_open/3.md), [dirfile(5)](/dirfile/5.md)