Copying parameters and fields

Parameters and fields have a defined data type (_DOUBLE, _REAL etc.). Families of subroutines are available for transferring the values of parameters, columns and fields between a catalogue and Fortran variables in an application program invoking the CAT interface. These Fortran variables may be of a variety of types. The type of the column or parameter need not correspond to the type of the Fortran variable; the interface will automatically attempt a type conversion. However, depending on the types involved, a conversion may not be possible for some values. The matrix of possibilities is shown in Table . This matrix is used for all conversions: both GET and PUT operations for both columns (or fields) and parameters.

Table: Conversion matrix for copying different types

Destination	Start or initial type
type	UBYTE	BYTE	UWORD	WORD	INTEGER	REAL	DOUBLE	LOGICAL	CHAR
UBYTE	yes	maybe	maybe	maybe	maybe	maybe	maybe	yes	maybe
BYTE	maybe	yes	maybe	maybe	maybe	maybe	maybe	yes	maybe
UWORD	yes	yes	yes	maybe	maybe	maybe	maybe	yes	maybe
WORD	yes	yes	maybe	yes	maybe	maybe	maybe	yes	maybe
INTEGER	yes	yes	yes	yes	yes	maybe	maybe	yes	maybe
REAL	yes	yes	yes	yes	yes	yes	maybe	yes	maybe
DOUBLE	yes	yes	yes	yes	yes	yes	yes	yes	maybe
LOGICAL	yes	yes	yes	yes	yes	yes	yes	yes	yes
CHAR	maybe	maybe	maybe	maybe	maybe	maybe	maybe	yes	maybe

Key:

yes

conversion is always possible,

maybe

conversion may be possible.

Note that converting a character string to a character string may result in an error because truncation may occur.

If a type conversion fails the appropriate exception value (null or locum, see Section , below) is substituted for the missing value. The error status is not set (that is, it remains ok) and no error message is generated. This procedure is followed consistently for all type conversions. It is adopted because, in practice, conversion failures are common.

The rules for converting to and from the _LOGICAL data type are as follows

From logical

 

• Conversion from LOGICAL to CHARACTER*$n$ gives `TRUE' or `FALSE' if $n$ is greater than or equal to 5 and `T' or `F' otherwise.

• Conversion from LOGICAL to INTEGER is defined such that true converts to 1 and false converts to 0.

• Conversion from LOGICAL to a numeric type except INTEGER is equivalent to converting LOGICAL to INTEGER and then INTEGER to the required numeric type.

To logical

 

• Any character string beginning with `T' (upper or lower case) converts to true; any other string converts to false.

• Any even INTEGER converts to false; any odd INTEGER converts to true (this behaviour is specified for compatibility with HDS).

• Conversion for other numeric types is equivalent to conversion from the type to INTEGER and then from INTEGER to LOGICAL.