The data type 'VARCHAR' may be used for the declaration of variables to which character strings of variable length are assigned. A VARCHAR declaration must contain at least either an array declarator or a pointer declarator. The last array declarator defines the maximum length ( <= 32767 ) of the variable. For a VARCHAR declaration with pointer declarator, the maximum length is undefined; the program has to assign storage space during runtime. The current length of a VARCHAR variable is defined by the length field, zero bytes are ignored in the calculation of the length. The precompiler replaces the declaration of VARCHAR variables by a structure declaration:
VARCHAR v {n}; is replaced by
struct {
unsigned short len;
unsigned char arr [n];
} v; where
len is assigned the current length
of the character string and
arr is assigned the characters.
VARCHAR *v; is replaced by
struct {
unsigned short len;
unsigned char arr [1];
} *v;
Examples of valid varchar declarations are:
VARCHAR a [21], b [100] [133]; /* a is a variable of length
21 and b an array of 100
elements of length 133 */
typedef VARCHAR LONGSTRING [ 65534 ]; /* type definition */
LONGSTRING c, d; /* c and d are variables of
type LONGSTRING */
typedef VARCHAR *PVC; /* definition of the pointer
type PVC */
PVC p; /* declaration of the VARCHAR
pointer p */
For example, the following statements can be used to assign storage space to p:
n = 100; /* maximum length of the VARCHAR variable */
p = (PVC) malloc (sizeof (p->len) + n * sizeof (p->arr));
VARCHAR pointers of a fixed maximum length can be declared in the following way:
typedef VARCHAR VC30 [30]; /* VARCHAR type of length 30 */
VC30 *q; /* q is a pointer to a VARCHAR of the
maximum length 30 */
The following statement is used to assign storage space to q:
q = (VC30* ) malloc (sizeof (VC30));