VXaddelem, VXlnkelem, VXdelelem − VisionX element manipulation functions

VisXelem_t *VXaddelem (lptr, vxtype, buf, size);
VisXelem_t *lptr;
int vxtype, size;
char *buf;
VisXelem_t *VXlnkelem (lptr, vxtype, buf, size);
VisXelem_t *lptr;
int vxtype, size;
char *buf;
VisXelem_t *VXdelelem (lptr);
VisXelem_t *list;

VisionX represents information internally as a doubly linked list of data elements. Each element contains a type descriptor, forward and backward pointers to other elements, and data. The VisionX file i/o functions read and write these lists.

The first element of a list is always a dummy element that is required for consistency. The element manipulation functions provide a set of programming tools for locating and performing operations on single list elements.

The element manipulation functions include the following: VXaddelem − add a new element after the given pointer position VXlnkelem − link a new element after the given pointer position and VXdelelem − delete the current element.

VXaddelem adds a new data element AFTER the element pointed to by lptr. The contents of the element are specified by the remaining arguments. vxtype specifies the VisionX type of the element, buf is a pointer to a buffer where the data is contained, and size specifies the size of the data in buf (IN BYTES). VXaddelem creates the new element and copies the data from the data buffer. Note, if the base type of the element is a scalar (VX_SCALAR) then size specifies the value of the element and buf is ignored. Note, if the base type of the element is a null (VX_NULL) then both the arguments size and buf are ignored. VXaddelem returns a pointer to the new element.

VXlnkelem is similar in operation to VXaddelem with the difference that the data buffer specified by buf is simply linked (pointed to) by the new element. Note, buf MUST have been previously dynamically allocated with Vmalloc. VXlnkelem may frequently be used instead of VXaddelem and is useful for efficiency because it avoids copying the data array buf. However, the program is responsible for allocating the buffer and must not reuse or deallocate this buffer after the call to VXlnkelem. This function should only be used by experienced programmers.

VXdelelem deletes the element pointed to by the argument lptr. If there exists an element in the list following the element being deleted then a pointer to that element is returned. If the element being deleted is the last element in the list then a pointer to the previous element is returned. (If the list is empty then the dummy element is deleted and a null pointer (VXNIL) is returned).

A. P. Reeves