DIM
The DIM statement is used to declare a variable or a list of variables as a specified data type or to dimension $STATIC or $DYNAMIC arrays.
Syntax
Description
- Sets the INTEGER range of elements (indices) of a STATIC array. If only one number is used, the lowest boundary is 0 by default.
- When used before an array is dimensioned, OPTION BASE 1 can set the default lower boundary of arrays to 1.
- DIM SHARED shares variable values with sub-procedures without passing the value in a parameter.
- Use the AS keyword to define a variable or array type AS...
- QB64 variable types:
- _BIT (or use variable suffix `). An AS multiplier can be used for multiple bits. Ex: DIM variable AS _BIT * 8
- _BYTE (or use variable suffix %%)
- _INTEGER64 (or use variable suffix &&)
- _FLOAT (or use variable suffix ##)
- _OFFSET (or use variable suffix %&)
- DIM AS _MEM (the _MEM type has no type suffix).
- Note: When a variable has not been defined or has no type suffix, the type defaults to SINGLE.
- When using the AS type variable-list syntax, type symbols cannot be used.
- When the $DYNAMIC metacommand or REDIM is used, array element sizes are changeable (not $STATIC).
- Use REDIM instead of DIM to dimension arrays as dynamic without the $DYNAMIC metacommand.
- Use REDIM _PRESERVE in QB64 to retain previous array values when changing the size of an array.
- REDIM _PRESERVE cannot change the number of array dimensions. An error will occur.
- Dynamic arrays MUST be REDIMensioned if ERASE or CLEAR are used, as the arrays are completely removed.
- All numerical variable types except SINGLE, DOUBLE and _FLOAT can be dimensioned as _UNSIGNED (suffix ~) or positive only.
- NOTE: Many QBasic keyword variable names can be used with a STRING suffix ($). You cannot use them without the suffix, use a numerical suffix or use DIM, REDIM, _DEFINE, BYVAL or TYPE variable AS statements. Although possible, it's recommended to avoid using reserved names.
- Warning: Do not use negative array upper bound index values, or OS access or "Out of Memory" errors will occur.
Examples
Example 1: Defines Qt variable as a one byte fixed length string.
DIM Qt AS STRING * 1 |
Example 2: Dimensions and types an array.
DIM Image(2000) AS INTEGER |
Example 3: Dimensions array with an INTEGER type suffix.
DIM Image%(2000) |
Example 4: Dimensions a range of array elements as SHARED integers.
DIM SHARED Image(1 TO 1000) AS INTEGER |
Example 5: Dimensions variable as an array of 8 elements of the type UNSIGNED BIT.
DIM bit(8) AS _UNSIGNED _BIT |
Example 6: QB64 is more flexible than QBasic when it comes to "Duplicate Definition" errors. The following code does not error:
x = 1 'x is a SINGLE variable PRINT x DIM x AS LONG PRINT x |
- Explanation: The SINGLE variable can be differentiated from the LONG x variable by using suffixes like x! or x& in later code.
Example 7: The following code will create a "Name already in use" status error in QB64 when the variable types are the same.
x = 1 'x is a SINGLE variable PRINT x DIM x AS SINGLE PRINT x |
- Explanation: QB64 gives an error because the creation of the new variable would make referring to the existing one impossible.
Example 8: Using QB64's alternative syntax to declare multiple variables/arrays of the same type.
DIM AS LONG w, h, id, weight, index 'all of these variables are created as type LONG DIM AS SINGLE x, y, z 'all of these variables are created as type SINGLE |
See also
- _DEFINE, _PRESERVE
- REDIM, TYPE
- ERASE, CLEAR
- DEFINT, DEFSNG, DEFLNG, DEFDBL, DEFSTR
- Mathematical Operations, Arrays
- Variable Types
- OPTION _EXPLICIT