SQL keyword protection and the dollar sign ($) symbol

All SQL statements within IBM® Informix® ESQL/C source files can either begin with the EXEC SQL key words or with the $ prefix. All of the following pairs of statements are equivalent:

EXEC SQL BEGIN DECLARE SECTION;
$BEGIN DECLARE SECTION;

EXEC SQL connect to ‘database9’;
$connect to ‘database9’;

EXEC SQL select fname into :hostvar1 from table1;
$ select fname into :hostvar1 from table1;

However, the $ symbol can also occur at the beginning of typedef definitions such as in the following example:

$int *ip = NULL;

In cases such as the preceding typedef example, program logic might require that the C preprocessor substitute the value zero in the place of the keyword NULL. Not allowing the C preprocessor to make value substitutions in such cases would lead to errors. Therefore, the eprotect utility does not add a prefix to the SQLKEYWORD_ prefix on SQL keywords that are displayed in SQL statements that begin with the dollar sign ($) symbol.