ASA Programming Guide
  Embedded SQL Programming
    Using host variables

C host variable types

Only a limited number of C data types are supported as host variables. Also, certain host variable types do not have a corresponding C type.

Macros defined in the sqlca.h header file can be used to declare host variables of the following types: VARCHAR, FIXCHAR, BINARY, PACKED DECIMAL, LONG VARCHAR, LONG BINARY, or SQLDATETIME structure. They are used as follows:

EXEC SQL BEGIN DECLARE SECTION;
DECL_VARCHAR( 10 ) v_varchar;
DECL_FIXCHAR( 10 ) v_fixchar;
DECL_LONGVARCHAR( 32678 ) v_longvarchar;
DECL_BINARY( 4000 ) v_binary;
DECL_LONGBINARY( 128000 ) v_longbinary;
DECL_DECIMAL( 10, 2 ) v_packed_decimal;
DECL_DATETIME v_datetime;
EXEC SQL END DECLARE SECTION;

The preprocessor recognizes these macros within a declaration section and treats the variable as the appropriate type.

The following table lists the C variable types that are allowed for host variables and their corresponding embedded SQL interface data types.

short i;
short int i;
unsigned short int i;

long l;
long int l;
unsigned long int l;

float f;

double d;

DECL_DECIMAL(p,s)

char a; /*n=1*/ 
DECL_FIXCHAR(n) a;
DECL_FIXCHAR a[n];

char a[n]; /*n>=1*/

char *a;

DECL_VARCHAR(n) a;

DECL_BINARY(n) a;

DECL_DATETIME a;

DECL_LONGVARCHAR( n ) a;

DECL_LONGBINARY( n ) a;

Pointers to char 

A host variable declared as a pointer to char (char *a) is considered by the database interface to be 32 767 bytes long. Any host variable of type pointer to char used to retrieve information from the database must point to a buffer large enough to hold any value that could possibly come back from the database.

This is potentially quite dangerous because somebody could change the definition of the column in the database to be larger than it was when the program was written. This could cause random memory corruption problems. If you are using a 16-bit compiler, requiring 32 767 bytes could make the program stack overflow. It is better to use a declared array, even as a parameter to a function, where it is passed as a pointer to char. This lets the PREPARE statements know the size of the array.