Definition status: Declared and Defined

A named item or item referenced by a passed parameter may be declared but may never have had any data put into it or may be both declared and have data.  A conditional can be structured to test whether an argument or named item was ever defined or declared.  The syntax then would be one of the following

$If declared itemname gamsstatement

which tests whether the item has been declared in a set, parameter, table, model, equation, file, acronym, or variable statement

$If defined itemname gamsstatement

that tests whether the item has been defined with data somewhere.

Example

(basicif.gms)

set aaa;

scalar bbb /1/;

$If not declared aaa display 'aaa is not declared';

$If not declared bbb display 'bbb is not declared';

$If not declared ccc display 'ccc is not declared';

$If not defined  aaa display 'aaa is not defined';

$If not defined  bbb display 'bbb is not defined';

$If not defined  ccc display 'ccc is not defined';

yields

59  set aaa;

60  scalar bbb /1/;

63  display 'ccc is not declared';

64  display 'aaa is not defined';

66  display 'ccc is not defined';

where aaa has no data (in this case no assigned set elements) and the $If causes generation of an action (in this case a display) since it is not being defined and the ccc tests generate both messages since it is not mentioned anywhere.