Datasheet

DURATION
Duration, closely related to a storage class, defines a period during which the
declared identifiers have real, physical objects allocated in memory. We also distin-
guish between compile-time and run-time objects. Variables, for instance, unlike
typedefs and types, have real memory allocated during run time. There are two
kinds of duration: static and local.
Static Duration
Memory is allocated to objects with static duration as soon as execution is under-
way; this storage allocation lasts until the program terminates. Static duration
objects usually reside in fixed data segments allocated according to the memory
model in force. All globals have static duration. All functions, wherever defined, are
objects with static duration. Other variables can be given static duration by using the
explicit static or extern storage class specifiers.
In the mikroC PRO for AVR, static duration objects are not initialized to zero (or null)
in the absence of any explicit initializer.
Don’t mix static duration with file or global scope. An object can have static duration
and local scope – see the example below.
Local Duration
Local duration objects are also known as automatic objects. They are created on the
stack (or in a register) when an enclosing block or a function is entered. They are
deallocated when the program exits that block or function. Local duration objects
must be explicitly initialized; otherwise, their contents are unpredictable.
The storage class specifier
auto can be used when declaring local duration vari-
ables, but it is usually redundant, because auto is default for variables declared
within a block.
An object with local duration also has local scope because it does not exist outside
of its enclosing block. On the other hand, a local scope object can have static dura-
tion. For example:
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CHAPTER 5