Declaration of host variables as pointers in C and C++ embedded SQL applications

You can declare host variables as pointers to specific data types. However, there are some formatting guidelines that you should be aware of.

Before you can declare a host variable pointer, you must consider the following restrictions:

If a host variable is declared as a pointer, no other host variable can be declared with that same name within the same source file. The following example is not allowed:
```
   char mystring[20]; 
   char (*mystring)[20];
```
Use parentheses when declaring a pointer to a null-terminated character array. In all other cases, parentheses are not allowed. For example:
```
   EXEC SQL BEGIN DECLARE SECTION; 
     char  (*arr)[10];  /* correct   */ 
     char  *(arr);      /* incorrect */ 
     char  *arr[10];    /* incorrect */ 
   EXEC SQL END DECLARE SECTION;
```
The first declaration is a pointer to a 10-byte character array. This is a valid host variable. The second is not a valid declaration. The parentheses are not allowed in a pointer to a character. The third declaration is an array of pointers. This is not a supported data type.
The host variable declaration:
```
  char *ptr; 
```
is accepted, but it does not mean null-terminated character string of undetermined length. Instead, it means a pointer to a fixed-length, single-character host variable. This might not be what is intended. To define a pointer host variable that can indicate different character strings, use the first declaration form shown previously in this topic.

When pointer host variables are used in SQL statements, they should be prefixed by the same number of asterisks as they were declared with, as in the following example:

   EXEC SQL BEGIN DECLARE SECTION; 
     char (*mychar)[20];    /* Pointer to character array of 20 bytes */ 
   EXEC SQL END DECLARE SECTION; 
     
   EXEC SQL SELECT column INTO :*mychar FROM table;   /* Correct */

Only the asterisk can be used as an operator over a host variable name.
The maximum length of a host variable name is not affected by the number of asterisks specified, because asterisks are not considered part of the name.
Whenever using a pointer variable in an SQL statement, you should leave the optimization level precompile option (OPTLEVEL) at the default setting of 0 (no optimization). This means that no SQLDA optimization will be done by the database manager.