REDIM
Revision as of 13:54, 22 July 2013 by imported>Clippy
A REDIM statement can re-dimension one dynamic(flexible) array or a comma separated list of arrays.
Syntax
- REDIM [_PRESERVE] [SHARED] ArrayName[typesuffix] ({max_element|low_element[TO upper_element, ...]}) [AS Type]
Description
- Can change the number of elements in an array (the present array data is lost unless _PRESERVE is used).
- Dynamic array elements can also be sized or resized by a program user's entry.
- The _PRESERVE option also allows the element range values to be moved upward or downward in QB64 only!
- Array is the name of the array to be dimensioned or re-dimensioned.
- elements is the number of elements the array should hold. Use the optional TO elements2 to set a range.
- Always use the same array TYPE suffix (AS type) or a new array type with the same name may be created.
- REDIM cannot change $STATIC arrays created with a DIM statement unless the $DYNAMIC Metacommand is used!
- To create a dynamic array use the $DYNAMIC metacommand or use REDIM rather than DIM when first creating the array.
- Use REDIM _PRESERVE to change the range or number of array elements without losing the remaining elements. Data may move up or down to accommodate those boundary changes.
- REDIM _PRESERVE cannot change the number of array dimensions or type!
- Dynamic arrays MUST be REDIMensioned if ERASE or CLEAR are used to clear the arrays as they no longer exist.
- When AS is used to declare the type, use AS to retain that type or it will change to SINGLE!
- NOTE: Many Qbasic keyword variable names CAN be used with a STRING suffix($) ONLY! You CANNOT use them without the suffix, use a numerical suffix or use DIM, REDIM, _DEFINE, BYVAL or TYPE variable AS statements!
- Warning! Do not use negative array upper bound index values as OS access or "Out of Memory" errors will occur!
Example 1: The $DYNAMIC Metacommand allows an array to be re-sized using DIM and REDIM.
'$DYNAMIC INPUT "Enter array size: ", size DIM Array(size) REDIM Array(2 * size) PRINT UBOUND(Array)
Example 2: Shows the difference between REDIM and REDIM _PRESERVE.
REDIM array(20) array(10) = 24 PRINT array(10) REDIM _PRESERVE array(30) PRINT array(10) REDIM array(15) PRINT array(10)
24 24 0
- Explanation: REDIM without _PRESERVE erases the array data and cannot change the number of dimensions.
See also
