Storage Classes
Visibility and lifetime of variables, objects and arrays
A variable, object or array's storage class determines when and where memory is allocated for it and when that memory is destroyed. There are 2 storage classes in FreeBASIC: automatic and static.
Automatic variable, object and array lifetimes begin at the point of declaration and end when leaving the scope they are declared in.
Automatic entities are guaranteed to have unique storage for each instance of the block in which they are declared. For example, the automatic variables declared within a procedure will be allocated at different addresses and have unique state (value) for each call to the procedure.
Automatic variables, objects and arrays are defined using the Dim, ReDim and Var keywords without the Shared specifier.
The memory for automatic variables, objects and arrays is allocated on the program stack.
Automatic variables, objects and arrays have no linkage.
Static variable, object and array lifetimes begin at program creation and end with program termination.
Static entities are guaranteed to have the same storage for each instance of the block in which they are declared. For example, the static variables declared within a procedure will be allocated at the same address, and retain their state (value) across each call to the procedure.
Static variables, objects and arrays are declared using the Static keyword. Entities declared using the Shared specifier are implicitly static. All entities declared within a procedure that is declared using the Static specifier are also implicitly static.
The memory for static variables, objects and arrays is allocated in the .BSS section of the executable, or in the .DATA section if they are initialized when defined. Static variable-length arrays must be declared empty, with an empty subscript range list; their element data is still allocated in the free store (when they are resized), but the internal array data is allocated in the .DATA section of the executable to allow the element data to persist throughout program execution.
Static variables, objects and arrays have internal linkage by default, unless previously declared using the Extern or Common keywords.
A variable, object or array's storage class determines when and where memory is allocated for it and when that memory is destroyed. There are 2 storage classes in FreeBASIC: automatic and static.
Automatic
Automatic variable, object and array lifetimes begin at the point of declaration and end when leaving the scope they are declared in.
Automatic entities are guaranteed to have unique storage for each instance of the block in which they are declared. For example, the automatic variables declared within a procedure will be allocated at different addresses and have unique state (value) for each call to the procedure.
Automatic variables, objects and arrays are defined using the Dim, ReDim and Var keywords without the Shared specifier.
The memory for automatic variables, objects and arrays is allocated on the program stack.
Automatic variables, objects and arrays have no linkage.
Static
Static variable, object and array lifetimes begin at program creation and end with program termination.
Static entities are guaranteed to have the same storage for each instance of the block in which they are declared. For example, the static variables declared within a procedure will be allocated at the same address, and retain their state (value) across each call to the procedure.
Static variables, objects and arrays are declared using the Static keyword. Entities declared using the Shared specifier are implicitly static. All entities declared within a procedure that is declared using the Static specifier are also implicitly static.
The memory for static variables, objects and arrays is allocated in the .BSS section of the executable, or in the .DATA section if they are initialized when defined. Static variable-length arrays must be declared empty, with an empty subscript range list; their element data is still allocated in the free store (when they are resized), but the internal array data is allocated in the .DATA section of the executable to allow the element data to persist throughout program execution.
Static variables, objects and arrays have internal linkage by default, unless previously declared using the Extern or Common keywords.
Platform Differences
- In DOS and Windows platforms, the size of the program stack can be adjusted at compile-time using the -t command-line switch. In Linux platforms, the size of the program stack can be adjusted at load-time by modifying /etc/security/limits.conf, or on a per-thread basis using the shell builtin ulimit.
Differences from QB
- QuickBASIC allows static entities to be declared within procedures and DEF FN routines only.
See also
