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 COMMON [SHARED] [/blockname/] variablelist
 
 Usage Notes
   ■ Use DIM rather than COMMON when you want to share access to variables
     within a single module. See: ◄DIM Statement►
 
   ■ When using COMMON SHARED to share arrays between forms, the correct
     syntax is:
 
         COMMON SHARED MyArray() AS INTEGER
 
     This statement must appear at the module level of all forms that will
     share the array. Use REDIM in a Form_Load event procedure to dimension
     the array. See: ◄REDIM Statement►
 
   ■ Errors caused by mismatched COMMON statements are subtle and difficult
     to find. You can avoid mismatched COMMON statements by:
     • Placing COMMON declarations in a single include file
     • Using the $INCLUDE metacommand in each module
     See: ◄$INCLUDE Metacommand►
 
   ■ The following code fragment shows how to use the $INCLUDE metacommand
     to share a file containing COMMON statements among programs:
 
         '$INCLUDE:'COMDEF.BI'         ' This file is MENU.BAS
         .
         .
         .
         CHAIN "Prog1"
         END
 
         '$INCLUDE:'COMDEF.BI'         ' This file is PROG1.BAS
         .
         .
         .
         END
 
         DIM A(100),B$(200)            ' This file is COMDEF.BI
         COMMON I,J,K,A()
         COMMON A$,B$(),X,Y,Z          ' End COMDEF.BI
 
   ■ When you compile a program using the Visual Basic Compiler (BC.EXE) with
     the /O option, common variables are not preserved across the chain. To
     preserve values across a chain, you must either:
     • Compile without the /O option (using BC)
     • Select the EXE Requiring Run-Time Module option from the Make EXE File
       dialog box (using VBDOS)
 
   ■ Unless it has been declared as a static array in a preceding DIM
     statement, an array variable in a COMMON statement is a dynamic array.
     Its dimensions must be set in a later DIM or REDIM statement.
     See: ◄DIM Statement►  ◄REDIM Statement►
 
   ■ Both static and dynamic arrays are placed in COMMON by using the array
     name followed by parentheses. Follow these rules when dimensioning an
     array:
     • For static arrays, dimensions must be set with integer-constant
       subscripts in a DIM statement preceding a COMMON statement
     • For dynamic arrays, dimensions must be set in a later DIM or REDIM
       statement
 
   ■ The elements of a dynamic array are not allocated in the COMMON block.
     Only an array descriptor is placed in COMMON.
 
   ■ A COMMON statement establishes storage for variables in a special area
     that allows them to be shared between modules or with other programs
     invoked with a CHAIN statement. See: ◄Using COMMON with CHAIN►
 
   ■ Because COMMON statements establish global variables for an entire
     program, they precede before any executable statements. All statements
     are executable except the following:
 
         COMMON                        CONST
         DATA                          DECLARE
         DEFtype                       DIM (for static arrays)
         $DYNAMIC                      $FORM
         $INCLUDE                      OPTION BASE
         OPTION EXPLICIT               REM
         SHARED                        $STATIC
         STATIC                        TYPE...END TYPE
 
   ■ When blockname is used, the COMMON block is a named COMMON block. When
     blockname is omitted, the block is a blank COMMON block. Items in a
     named COMMON block are not preserved across a chain to a new program.
     See: ◄Using Named COMMON►  ◄Using COMMON With CHAIN►
 
   ■ The size of a common area can be different from that in another module
     or chained program if a blank COMMON block has been used. When a Visual
     Basic program shares COMMON blocks with a routine in the user library,
     the calling program may not redefine the COMMON block to a larger size.
 
   ■ Use the blockname argument to share only specific groups of variables.
     You cannot use a type-declaration character (%, &, !, #, @, $) as part
     of blockname.
 
   ■ Variables in COMMON blocks are matched by position and type, not by
     name. Thus, variable order is significant in COMMON statements. For
     example, in the following fragment, the order of variables in COMMON
     statements links the variables, not the names:
 
         COMMON A, D, E                ' Module level
         A = 5 : D = 8 : E = 10
         .
         .
         .
         COMMON A, E, D                ' Common statement in another module
         .                             ' A = 5, E = 8, D = 10
         .
         .