UltraLite User's Guide
  The Embedded SQL Interface
    Using host variables

The scope of host variables

A host-variable declaration section can appear anywhere that C variables can normally be declared, including the parameter declaration section of a C function. The C variables have their normal scope (available within the block in which they are defined). However, since the SQL preprocessor does not scan C code, it does not respect C blocks.

The preprocessor assumes all host variables are global 

As far as the SQL preprocessor is concerned, host variables are globally known in the source module following their declaration. Two host variables cannot have the same name. The only exception to this rule is that two host variables can have the same name if they have identical types (including any necessary lengths).

The best practice is to give each host variable a unique name.

Examples 

• Because the SQL preprocessor can not parse C code, it assumes that all host variables, no matter where they are declared, are known globally following their declaration.

  // Example demonstrating poor coding
  EXEC SQL BEGIN DECLARE SECTION;
     long emp_id;
  EXEC SQL END DECLARE SECTION;
  long getManagerID( void )
  {
     EXEC SQL BEGIN DECLARE SECTION;
        long manager_id = 0;
     EXEC SQL END DECLARE SECTION;
     EXEC SQL   SELECT manager_id
              INTO :manager_id
              FROM employee
              WHERE emp_number = :emp_id;
     return( manager_number );
  }
  void setManagerID( long manager_id )
  {
     EXEC SQL   UPDATE employee
              SET manager_number = :manager_id
              WHERE emp_number = :emp_id;
  }

Although it works, the above code is confusing because the SQL preprocessor relies on the declaration inside getManagerID when processing the statement within setManagerID. You should rewrite this code as follows.

// Rewritten example
#if 0
   // Declarations for the SQL preprocessor
   EXEC SQL BEGIN DECLARE SECTION;
      long emp_id;
      long manager_id;
   EXEC SQL END DECLARE SECTION;
#endif
long getManagerID( long emp_id )
{
   long manager_id = 0;
   EXEC SQL   SELECT manager_id
            INTO :manager_id
            FROM employee
            WHERE emp_number = :emp_id;
   return( manager_number );
}
void setManagerID( long emp_id, long manager_id )
{
   EXEC SQL   UPDATE employee
            SET manager_number = :manager_id
            WHERE emp_number = :emp_id;
}

The SQL preprocessor sees the declaration of the host variables contained within the #if directive because it ignores these directives. On the other hand, it ignores the declarations within the procedures because they are not inside a DECLARE SECTION. Conversely, the C compiler ignores the declarations within the #if directive and uses those within the procedures.

These declarations work only because variables having the same name are declared to have exactly the same type.