Understanding the lifetime of variables
The time during which a variable retains its value is known as its lifetime. The value of a variable may change over its lifetime, but it retains some value. When a variable loses scope, it no longer has a value.
When a procedure begins running, all variables are initialized. A numeric variable is initialized to zero, a variable-length string is initialized to a zero-length string (""), and a fixed-length string is filled with the character represented by the ASCII character code 0, or Chr( 0 ). Variant variables are initialized to Empty. Each element of a user-defined type variable is initialized as if it were a separate variable.
When you declare an object variable, space is reserved in memory, but its value is set to Nothing until you assign an object reference to it by using the Set statement.
If the value of a variable isn't changed during the running of your code, it retains its initialized value until it loses scope.
A procedure-level variable declared with the Dim statement retains a value until the procedure is finished running. If the procedure calls other procedures, the variable retains its value while those procedures are running as well.
If a procedure-level variable is declared with the Static keyword, the variable retains its value as long as code is running in any module. When all code has finished running, the variable loses its scope and its value. Its lifetime is the same as a module-level variable.
A module-level variable differs from a static variable. In a standard module or a class module, it retains its value until you stop running your code. In a class module, it retains its value as long as an instance of the class exists. Module-level variables consume memory resources until you reset their values, so use them only when necessary.
If you include the Static keyword before a Sub or Function statement, the values of all the procedure-level variables in the procedure are preserved between calls.
See also
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